Transmission Media Filka

FACULTY OF ELECTRICAL ENGINEERING AND COMMUNICATION BRNO UNIVERSITY OF TECHNOLOGY

TRANSMISSION MEDIA

Author: Assoc. Prof. Miloslav Filka, Ph.D.

Brno 2010

Faculty of Electrical Engineering and Communication, Brno University of Technology 1

Contents

1 Introduction 7

2 Enlistment of the study to educational programme 82.1 Introduction into study . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82.2 Entry test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

3 Analysis of line 83.1 Basic relations of homogenous line . . . . . . . . . . . . . . . . . . . . . . . 83.2 Infinite homogenous line . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103.3 Relations of voltage vs. current in the entry and termination of line . . . . 133.4 Phase and group velocity of propagation . . . . . . . . . . . . . . . . . . . 143.5 Delay of signal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163.6 Input impedance of homogenous line terminated variably . . . . . . . . . . 17

3.6.1 Termination impact of Infinite line . . . . . . . . . . . . . . . . . . 173.6.2 Input impedance of finite line, terminated by impedance Z2 = Zc . 173.6.3 Input impedance of open-line . . . . . . . . . . . . . . . . . . . . . 183.6.4 Input impedance of short-line . . . . . . . . . . . . . . . . . . . . . 183.6.5 Input impedance of line terminated by common impedance Z2 6= Zc 20

3.7 Lines practically infinite . . . . . . . . . . . . . . . . . . . . . . . . . . . . 213.8 Electrically short lines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 213.9 Frequency dependencies of primary and secondary parameters of various

line types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 223.9.1 Air lines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 233.9.2 Cable lines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

3.10 Homogenous line by high frequencies . . . . . . . . . . . . . . . . . . . . . 353.10.1 HF open line . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 363.10.2 HF shortcut line . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

3.11 Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

4 Types of metallic lines and cables 424.1 Open air lines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 424.2 Cable lines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 434.3 Electrical attributes of metallic lines . . . . . . . . . . . . . . . . . . . . . 494.4 Coiled cables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 524.5 Symmetrical HF cables and cables for digital transmission . . . . . . . . . 574.6 Coaxial cables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 574.7 Special cables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 604.8 Structured cabling systems . . . . . . . . . . . . . . . . . . . . . . . . . . . 634.9 xDSL Transmitting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 664.10 Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67

Transmission Media 2

5 Shortcomings of telecommunication cables and Inhomogeneities 685.1 Non-homogeneities of cables . . . . . . . . . . . . . . . . . . . . . . . . . . 685.2 Non-homogeneities of cables . . . . . . . . . . . . . . . . . . . . . . . . . . 685.3 Asymmetry of capacities and leakages . . . . . . . . . . . . . . . . . . . . . 705.4 Magnetic asymmetries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 735.5 Corrective measures of asymmetry . . . . . . . . . . . . . . . . . . . . . . . 745.6 Non-homogeneities of lines . . . . . . . . . . . . . . . . . . . . . . . . . . . 765.7 Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78

6 Wireless transmissions 796.1 Radio transmissions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 796.2 Satellite transmissions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 796.3 Mobile transmissions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 806.4 Optical transmissions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80

7 Optical fibres and cables 807.1 Basic principles of transmission . . . . . . . . . . . . . . . . . . . . . . . . 807.2 Types of optical fibres . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 837.3 Theory of optical transmission, loss and dispersion . . . . . . . . . . . . . . 897.4 Optical cables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 917.5 Practical usage of optical fibres for high bit rate transmission . . . . . . . . 102

7.5.1 Optical access networks . . . . . . . . . . . . . . . . . . . . . . . . 1087.5.2 Triple Play services in FTTH systems . . . . . . . . . . . . . . . . . 114

7.6 Exercises . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 120

8 Appendix 1208.1 Exercises results of chapter 3.11 . . . . . . . . . . . . . . . . . . . . . . . . 1208.2 Exercises results of chapter 4.10 . . . . . . . . . . . . . . . . . . . . . . . . 1208.3 Results of examples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1208.4 Exercises results of chapter 7.6 . . . . . . . . . . . . . . . . . . . . . . . . . 121


List of Figures

3.1 Model of homogeneous line . . . . . . . . . . . . . . . . . . . . . . . . . . . 93.2 Voltage conditions alongside infinite line . . . . . . . . . . . . . . . . . . . 123.3 Propagation velocity for linear relation β = ϕ(f) . . . . . . . . . . . . . . . 153.4 Velocity of propagation influenced by frequency - concave curve vs. convex

curve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163.5 Functions of tghγ1 and cotghγ1 to a . . . . . . . . . . . . . . . . . . . . . 193.6 Various characters of lines . . . . . . . . . . . . . . . . . . . . . . . . . . . 233.7 Frequency relation to primary parameters of air lines . . . . . . . . . . . . 233.8 Dependence of specific loss and shift on fair lines . . . . . . . . . . . . . . 243.9 Attenuation of air line (bronz 3 mm) . . . . . . . . . . . . . . . . . . . . 263.10 Impedance of air and cable lines depending on frequency . . . . . . . . . . 273.11 Frequency dependency α, β and Zc for couple types of coiled lines . . . . . 283.12 Relation of specific attenuation to frequency α . . . . . . . . . . . . . . . . 303.13 Dependence of specific shift β on frequency . . . . . . . . . . . . . . . . . . 333.14 Dependence of ReZc and ImZc on frequency . . . . . . . . . . . . . . . . . 333.15 Frequency dependency of coaxial cable primary parameters is real (Zc

.= 75 Ω) 34

3.16 Frequency dependencies α and β of coaxial and cable - 1,2/4,4 (little),2,6/9,4(medium) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

3.17 Frequency dependencies Zc = ϕ(f) for little and medium coaxial pairs . . . 353.18 Circumstances in extra high voltage by HF current transmission . . . . . . 363.19 Conditions for modulation of wire radio transmission . . . . . . . . . . . . 373.20 Standing wave of voltage and current of open HF line . . . . . . . . . . . . 393.21 Dependence of Z1p for various lengths of HF open line . . . . . . . . . . . . 403.22 Standing wave of voltage and current of open HF line . . . . . . . . . . . . 403.23 Four wave band pass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 413.24 Quarter wave band stop . . . . . . . . . . . . . . . . . . . . . . . . . . . . 413.25 Waveguide principle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 424.1 Construction of a) DM quad, b) cross quad . . . . . . . . . . . . . . . . . . 434.2 Wrapping of wire by cord . . . . . . . . . . . . . . . . . . . . . . . . . . . 454.3 Profile of cable . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 454.4 Composition of elements into cable profile . . . . . . . . . . . . . . . . . . 464.5 Principle of coiled line . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 534.6 Dependency of specific loss for coiled line on x . . . . . . . . . . . . . . . . 544.7 Method of phantom and superphantom composition . . . . . . . . . . . . . 564.8 Coaxial pair . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 584.9 Composition of coaxial cable core . . . . . . . . . . . . . . . . . . . . . . . 604.10 Self-contained hanged cable . . . . . . . . . . . . . . . . . . . . . . . . . . 614.11 Hanging (catenary) cable . . . . . . . . . . . . . . . . . . . . . . . . . . . . 614.12 Metallic radial waveguide . . . . . . . . . . . . . . . . . . . . . . . . . . . . 624.13 Spiral waveguide . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 624.14 Outlet assignment of cabling 5-UTP . . . . . . . . . . . . . . . . . . . . . . 644.15 Scheme of cabling system . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65


4.16 Scheme of cabling system: CR - campus cabinet, RR - backbone cabinet,HR -horizontal cabinet, Z - sockets . . . . . . . . . . . . . . . . . . . . . . 66

4.17 Trends of bit rate upgrade . . . . . . . . . . . . . . . . . . . . . . . . . . . 675.1 Scheme of partial capacities inside cable quad . . . . . . . . . . . . . . . . 705.2 Partial capacities transformed from star of four earth capacities to full

polygon . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 715.3 Network of effective partial capacities inside cable quad . . . . . . . . . . . 715.4 Capacitive bridge of effective partial capacities of quad . . . . . . . . . . . 725.5 Fictional capacitive coupling k‘1 . . . . . . . . . . . . . . . . . . . . . . . . 725.6 Capacitive asymmetry k1 and functional capacity C.l of manufactured length 735.7 a) Partial inductive couplings among wires of unique quad, b) fictional

inductive coupling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 745.8 Resistive and inductive asymmetries of 1st and 2nd pairs . . . . . . . . . . . 755.9 Scheme of reflected waves of voltage and current of impedance non-homogeneities 775.10 Undulated characteristic impedance around its mean value . . . . . . . . . 776.1 Scheme of radio link system . . . . . . . . . . . . . . . . . . . . . . . . . . 797.1 Basic scheme of optical link . . . . . . . . . . . . . . . . . . . . . . . . . . 817.2 Transmission by optical waveguide . . . . . . . . . . . . . . . . . . . . . . 827.3 Single-mode lightguide . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 837.4 Multi-mode step indexed optical waveguide . . . . . . . . . . . . . . . . . . 837.5 Gradient multi-mode optical waveguide . . . . . . . . . . . . . . . . . . . . 847.6 Refraction index of SM fibre . . . . . . . . . . . . . . . . . . . . . . . . . . 857.7 Profile of refraction index for DC . . . . . . . . . . . . . . . . . . . . . . . 877.8 Loss characteristics of optical waveguide . . . . . . . . . . . . . . . . . . . 907.9 Curve of chromatic dispersion . . . . . . . . . . . . . . . . . . . . . . . . . 917.10 Various designs of optical fibre cables a, b, c,... . . . . . . . . . . . . . . . . 927.11 Grooved construction of cable . . . . . . . . . . . . . . . . . . . . . . . . . 937.12 RIBBON cable - banded . . . . . . . . . . . . . . . . . . . . . . . . . . . . 937.13 Cable OPTION1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 977.14 Self-contained optical cable . . . . . . . . . . . . . . . . . . . . . . . . . . . 977.15 Optical cable Mini-LXE . . . . . . . . . . . . . . . . . . . . . . . . . . . . 987.16 Indoor optical cable . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1007.17 Optical joint . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1017.18 Optical distribution frames . . . . . . . . . . . . . . . . . . . . . . . . . . . 1027.19 Scheme of optical link with wave division multiplex . . . . . . . . . . . . . 1037.20 Wave multiplex (Coupler) . . . . . . . . . . . . . . . . . . . . . . . . . . . 1057.21 WDM JDS FITEL (1533/1541/1549/1557 nm) . . . . . . . . . . . . . . . . 1057.22 OLS 806 in ”ring application” . . . . . . . . . . . . . . . . . . . . . . . . . 1067.23 WDM spectrum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1067.24 Scheme of optical amplifier . . . . . . . . . . . . . . . . . . . . . . . . . . . 1077.25 Realisation and scheme of WDM in UTKO network . . . . . . . . . . . . . 1077.26 Block scheme of access network . . . . . . . . . . . . . . . . . . . . . . . . 1087.27 Block scheme access network AON. . . . . . . . . . . . . . . . . . . . . . . 1107.28 Downstream transmission scheme between OLT and ONU units . . . . . . 111


7.29 Upstream transmission scheme between ONU a OLT units . . . . . . . . . 1117.30 Topologies used in PON networks, a) bus, b) p2p, c) star, d) ring . . . . . 1127.31 Transmission bit rates offered to user by symmetric services split 1:32 . . . 1147.32 Scheme of Triple Play services processing by systems FTTH (source: EXFO)1167.33 Exemplification of PLC and FBT splitter structures . . . . . . . . . . . . . 117


List of Tables

3.1 Types of coiled lines and their attributes . . . . . . . . . . . . . . . . . . . 327.1 Parameters of passive optical networks single specification . . . . . . . . . 1137.2 Basic and extended Triple Play services . . . . . . . . . . . . . . . . . . . . 1157.3 Inserted loss values for PLC splitter Telcordia GR-1209 . . . . . . . . . . 1167.4 Evaluation of requirements for overlay PON (analogous video) and switched

TV (Digital video) onto transmitting optical powers . . . . . . . . . . . . . 119


1 Introduction

The item ”Transmitting media” introduces students into wide range of knowledge fortransmitting of various types of information. Seen by the historical point of view, me-dia for information transmitting are closely connected with invention of the telegraph(Samuel Morse, 1832) using one wire line with earth as backhauling conductor. Intensivedevelopment of telegraph was launched subsequently; Europe was linked with America in1858. The invention of telephone (Alexander Graham Bell, 1876) initiated developmentof telephone lines. The following invention of wireless transmission (Guglielmo Marconi,1901) launched stormy development of this type of transmitting. The finding of shortwaves (1926) enables first of all intercontinental transmissions (1927 - England - USA).Next research and development returns focusing to coaxial cables opening new horizonsin quality as well as reliability of transmitting. First coaxial cable connecting Europe andAmerica (1956), known as TAT-7 enabled transmission of 36 analogue telephone channels.Next step are satellites (1961). Everybody is impressed, that most perspective connec-tion has been entered the scene.... The last coaxial cable (TAT-10) was installed in 1983.Transmitting capacity performs 4200 telephone channels, repeating step is 9 km. The newphenomenon has been coming in this moment: - optical fibre. Extreme broad bandwidthenables transmission of large informational capacity, otherwise high bit rates supportedby excellent reliability, immunity to disturbances and tapping including very light weight.First optical transatlantic submarine cable TAT-8 was introduced in 1988. The very lastinstalled TAT 12-13, equipped by optical amplifiers using ring topology, enables bit rate2,5 Gbit/s, accordingly 38000 digital telephone channels. Following upgrade came withwave multiplexing (WDM). The transmitting capacity may be enlarged 4x, 8x, 40x andexpressed in telephone channels maybe one million could be reached. Transfer to fibreoptics is comparable with change of simple walking for the plane. Despite technical fea-tures of fibre optics seems to be infinite, we are obliged to integrate its costs into balancesheet. We try to reach extreme bit rates in closing metallic last mile - using precioustechnology for so called structured cabling systems as well as utilising of new types ofsophisticated modulations of xDSL. Systems xDSL are able to exploit existing accessnetworks - the comparison to dug-in gold due to the extreme costs of cable laying. Asit was mentioned before, transmitting media is linkage agent between two points, cities,state and continents. These connections are determined by international cooperation intechnical standardisation, design, maintainance, billing etc. Therefore the InternationalTelecommunication Union (Telegraph originally) was founded in 1865 already. (May 17this celebrated as an World Day of Telecommunication) ITU is seated in Geneva, Switzer-land. ITU is technical organisation of United Nations since 1947 being obliged to keepand broaden international cooperation in upgrading of all types of telecommunicationservices, supporting deployment of technical means as well as its exploiting. ITU is in-volved in allocation of frequency bandwidths, in prevention of disturbances of all wirelessservices, by tariffing, support of investments, deployment and upgrading of telecommuni-cation equipment in developing countries. Two commissions are active actually: ITU-T(telecommunication) and ITU-R (radiocommunication). Their outputs are published inRecommendations in so called ”coloured” books. These Recommendations are manda-


tory being authorised by the Council of Government Deputies of individual member states.(once within 5 years by presence of all states of the world). Well known are former ab-breviations CCITT, CCIR - in French: Comit Consultatif International Tlgraphique etTlphonique, Radionique). The item introduces individual transmitting media as follows.Theoretical knowledge is amended by laboratory exercises; there are focused for gainingpractical skills in installing of optical fibres (welding, quality and fault measurements,simulation of systems). The text is printed without language editing. The firts draft.

2 Enlistment of the study to educational programme

2.1 Introduction into study

The item is registered as optional in summer semester of 2nd year of Bc studies. It offersbasis for majority of lectured items as communication technologies, data communication,network architecture in the same year as well as for following items in next years of studies.

2.2 Entry test

There is proposed to be precise following consultations with lecturers of other items.

3 Analysis of line

3.1 Basic relations of homogenous line

Electrical attributes of line observed by transmitting point of view are characterised byprimary parameters: resistance R[Ω/km], inductance L[H/km], capacitance C[F/km]and conductance G[S/km]. These parameters are independent of voltage as well as trans-mitted current; there are dependent of composition of line, used materials and last but notleast of frequency of transmitted signal. Concerning two conductor lines, the equivalentscheme is equal to the Fig. 3.1:

Decrease of voltage on element dx is

−dUxdx

= (R + jωL)Ix (3.1)

dually decrease of current

−dIxdx

= (G+ jωC)Ux. (3.2)

The solution of equations due to deriving equation (3.1) as per x

−d2Uxdx2

=dIxdx

(R + jωL). (3.3)


Figure 3.1: Model of homogeneous line

Using it to equation (3.2) we will obtain

−d2Uxdx

= −Ux[(R + jωL)(G+ jωC)]. (3.4)

Express

(R + jωL)(G+ jωC) = γ2 (3.5)

and we are able to adapt this equation into the following form

dUxdx2

− γ2Ux = 0.d2Uxdx2

(3.6)

Solution of this linear homogeneous differential equation of second rank is following:

Ux = A1eγx + A2e

−γx (3.7)

The value of Ix is to be calculated from (3.1)

Ix = − 1

R + jωL

dUxdx

(3.8)

Use for dUx/dx from equation (3.7) derived before as per x

dUxdx

= γA1eγx − γA2e

−γx

and

Ix =γ

R + jωL(−A1e

γx + A2e−γx) =

√G+ jωC

R + jωL(−A1e

eγx + A2e−γx). (3.9)

Bracket term is dimensioned in voltage (see 3.7) and therefore the term√G+ jωC

R + jωL=

√Y

Z(3.10)


is dimensioned as admittance.Its reciprocal value will be impedance and is called characteristic impedance Zc.

There is assigned by primary parameters R, L, C and G for specific line; for definedfrequency ω it is valid as follows:

Zc =

√R + jωL

G+ jωC=

√Z

Y. (3.11)

The equation (3.9) is to be expressed

Ix =1

Zc(−A1e

γx + A2e−γx) (3.12)

Integrating constants A1, A2 are assigned as to relations at the end of line for

x = 1 ; Ux = U2 ; Ix = I2

therefore

U2 = A1eγl + A2e

−γl (3.13)

and

ZcI2 = −A1eγl + A2e

−γl (3.14)

We will obtain by taking off (3.14) from (3.13)

A1 =1

2(U2 − ZcI2)e

−γl (3.15)

and dually by adding

A2 =1

2(U2 + ZcI2)e

γl. (3.16)

3.2 Infinite homogenous line

This type performs the most frequent type of line. For this case it is valid 1 = ∞ andtherefore

A1∞ = 0

And for (3.7) and (3.12) are following equations valid:

Ux∞ = A2e−γl (3.17)

Ix∞ =1

ZcA2e

−γl (3.18)


Integrating constant A2 is determined by relation in the beginning of line, where x = 0

U1∞ = A2 (3.19)

ZcI1∞ = A2 (3.20)

Inducting (3.19) into (3.17) and (3.20) into (3.18) is obtained

Ux∞ = U1∞e−γx (3.21)

Ix∞ = I1∞e−γx (3.22)

For this and before mentioned equations it is valid

γ =√

(R + jωL)(G+ jωC)

and performs complex magnitude, which may be expressed in following form

γ = α+ jβ. (3.23)

Denoting vector voltage in the beginning of infinite line as

U1∞ = |U1∞|ejϕl

and (3.23) is expressed as

e−γx = e−αxe−jβx (3.24)

then by substituting into (3.21) is obtained.

Ux∞ = |U1∞|e−αxej(ϕ1∞−βx) (3.25)

Equally for current is valid

Ix∞ = |I1∞|e−αxej(ψ1∞−βx). (3.26)

Left part of equation (3.25) performs amplitude of voltage in x, which is decliningexponentially as per

|Ux∞| = |U1∞|e−αx (3.27)

Parameter α is called specific loss quantified in dB/km and is changing with type ofline. The value α.l = a in dB (related to the lenght 1).

Second part of equation (3.25) expresses actual value of phase in place x, then

ejϕx∞ = ej(ϕ1∞−βx). (3.28)


It passes of this term, that by increasing x the phase of voltage vector is delayed byβx, where β is specific phase shift (being related with length is equal to β.1 = b phaseshift (l for both events in km).

The magnitude γ (3.5) is specific transfer dimension. Related to the length γ.l = git is called transfer rate. Therefore is valid too

g = γ.l = a+ jb. (3.29)

Above mentioned phenomenon is possible to express graphically. As is evident in Fig.3.2, the voltage |U1∞| is in the beginning of line. There is reduced in distance x fromthe beginning to the value |U1∞|e−αx and phase delayed by β.x. The value of voltage isdistant λ from the beginning |U1∞|e−αλ and phase is delayed by β · λ. There is possibleto express, that wave lenght λ is a distance, in the case the vector it is turned upon 360and is valid:

λ.β = 2π.

This screwed surface performs fully voltage vector running. There is evident, thatvoltage vector is decreasing alongside distance by geometrical sequence, phase delay byarithmetic sequence.

Let us observe once more equations (3.7) and (3.12). We can see, that they arecomposed of two components; first one, so called gradual, which is decreased equally todistance

Uxp = A2e−γx (3.30)

Figure 3.2: Voltage conditions alongside infinite line

Ixp =1

ZcA2e

−γx (3.31)

and reflected

Uxr = A1eγx, (3.32)


Ixr = − 1

ZcA1e

γx (3.33)

which is increasing alongside distance (decreasing from the termination to beginningof line).

The value of voltage (current) in any point x is given by vector multiplication of thesecomponents. Resulting magnitude and phase is done by magnitude and phase of reflectedwave.

Let us divide equation (3.17) by (3.18); we will obtain impedance in point x(Zx∞)

Zx∞ =Ux∞Ix∞

= Zc (3.34)

There is evident from this equation, that at point in distance x from the beginningof infinite line the impedance Z1∞ measured to termination of line is equal tocharacteristic impedanceZc. This characteristic impedance is independent of x (incontrary to DC resistance!)- there is certain value for specific type of line and specificfrequency. Let us divide equation (3.19) by (3.20) to obtain input impedance of infiniteline

Z1∞ =U1∞

I1∞= Zc (3.35)

The emerging conclusion of this equation implies, that input Z1∞ impedance of in-finite line is equal to characteristic impedance Zc. Characteristic impedance is ableto be directly measured as input impedance of infinite line (or line correctly terminated,adapted to impedance - see as follows), or maybe calculate using primary parameters R, L,C and G according to equation (3.11). Final notice: Magnitudes Zc and γ are collectivelydenominated as secondary parameters of line.

3.3 Relations of voltage vs. current in the entry and termina-tion of line

We are meeting events to appoint voltage U1 and current I1 in the beginning of homoge-neous line characterised by secondary parameters Zc, γ and longitude l, knowing voltageU2 and current I2 in the line termination. There is necessary to determine relations

U1 = f(U2, I2), I1 = fx(U2, I2)

We determine voltage and current by x = 0 using equations (3-7) and (3-12)

U1 = A1 + A2 (3.36)

and

I1 =1

Zc(−A1 + A2) (3.37)


We obtain by induction to A1 and A2 from (3.15) and (3.16)

U1 =U2 − ZcI2

2e−γl +

U2 + ZcI22

eγl = U2eγl + e−γl

2+ ZcI2

eγl + e−γl

2

prospectively

U1 = U2coshγl + ZcI2sinhγl. (3.38)

Likewise for

I1 =1

Zc[−U2 − ZcI2

2e−γ` +

U2 + ZcI22

eγl] =1

ZcU2eγl − e−γl

2+ I2

eγl + e−γl

2

eventually

I1 =U2

Zcsinhγl + I2coshγl (3.39)

Equations are able to be performed as

U1 = A11U2 + A12I2 (3.40)

I1 = A21U2 + A11I2 (3.41)

where

A11 = coshγl A12 = sinhγl A21 =1

Zcsinhγl

3.4 Phase and group velocity of propagation

We will explain these ideas using mutual context between phase constant β, wave lenghtλ and velocity of propagation v.

For phase constant β (constant of wave lenght) emerges from equation (3-28) and fromFig. 3.2 following relation

β · λ = 2π

lay down

λ =2π

β

In consequence with velocity

vf =λ

T= λ · f =

2π

β· ω2π

=ω

β(3.42)


we gain final expression for phase velocity of propagation.

There is necessary to realise, that all calculations were made for one frequency, butin reality complete frequency bands are transmitted. Therefore frequency dependence ofsecondary parameters are to be examined.

For example in case phase velocity is constant across whole band, it means that themost ideal situation is needed for transmitting. Then β is proportional directly to ωfollowing equation is valid:

β = kω. (3.43)

This event is performed in Fig.3.3.

Figure 3.3: Propagation velocity for linear relation β = ϕ(f)

For majority of events the relation is non-linear as β = ϕ(f) the curve (see Fig.3.4).This is to be expressed (3.42) by differentials.

vs =dω

dβ. (3.44)

This equation performs so called group velocity of propagation, therefore thevelocity is common ”group” of closely similar frequencies.

Two possible cases of frequency relations are demonstrated in Fig. 3.4.

β = ϕ(ω)

There is concave curve in Fig. 3.4 left, when dω/dβ = vs = tgψ velocity to frequencyis decreasing. On the other hand in the same Fig. 3.4 right velocity to frequency isincreasing. Phase distortion is emerging in both cases.


Velocity of propagation is approximate to the light velocity; for air lines roughly 280000km/s; on the other hand this velocity for coiled lines is significantly lower, maybe16 000km/s (depending on inductivity of coiling units). We can see, that velocity ofpropagation differs together with different wave length. Distances of lines are to berelated to wave lengths and not to metrical longitudes.

Figure 3.4: Velocity of propagation influenced by frequency - concave curve vs. convexcurve

3.5 Delay of signal

The delay of signal is used in practice for evaluation of propagation velocity. Outgoingfrom known relation for velocity, then signal delay is:

tf =l

vf

We obtain by vf institution of equation (3-42)

tf = ` · βω

=b

ω(3.45)

where b as we know is phase shift related to integral line. Analogical relation is validfor group delay using differentials

ts =db

dω. (3.46)

Appreciating reality, that according to equation (3-46) b = βl, then the curve of groupdelay is nothing else than derivation of phase characteristics. Realizing this treatment inFig. 3.4 it is evident, that group delay will be more important by low frequencies, thanby HF. There are defined maximal acceptable times of group delay (in ms) for variouslines of differed length (e.g. 2500 km).


3.6 Input impedance of homogenous line terminated variably

Input impedance of line Z1 for universal case depends on terminating impedance Z2.There is not equal to characteristic impedance Zc, as by infinite homogeneous line. Therelation for Z1 is to be expressed from equations (3.40) and (3.41)

Z1 =U1

I1=A11U2 + A12I2A21U2 + A11I2

(3.47)

Let us divide nominator as denominator I2 and induct Z2 into U2/I2

Z1 =A11Z2 + A12

A21Z2 + A11

=coshγ1Z2 + Zcsinhγ11Zc

sinhγ1Z2 + Zccoshγ1

and by another adjustment

Z1 = ZcZ2coshγ1 + Zcsinhγ1

Z2sinhγ1 + Zccoshγ1. (3.48)

We will be able to analyse another possible case using this equation.

3.6.1 Termination impact of Infinite line

We mentioned before, that Z1∞ = Zc in accordance with derived equation (3-35).Thesame result should be reached by analysis of (3.48). Hyperbolic sine and cosine of complexargument γ1 = (α + jβ)1 is changing being depend a as to Fig. 3.4. Since determinedvalue we can consider

coshγl = sinhγl = cosha = sinha (3.49)

Then for input impedance it is valid

Z1∞ = Zc(Z2 + Zc)coshαl

(Z2 + Zc)coshαl= Zc. (3.50)

There is evident, that input impedance Z1∞ is equal to characteristic impedance Zc,by any termination Zc. This is valid also for short cut line (Z2 = 0) as well as open line(Zc = ∞) .

3.6.2 Input impedance of finite line, terminated by impedance Z2 = Zc

Inducting Z2 = Zc into equation (3.48), we obtain

Z1 = ZcZc(coshγ1 + sinhγ1)

Zc(coshγ1 + sinhγ1)= Zc (3.51)

By termination of line by characteristic impedance, not respecting length of line theinput impedance is equal to characteristic one. This configuration of line is of the samebehaviour as infinite line; the only difference is in fact, that voltage and current at theend of line are finitely valued. No reflections are inflicted at the end (so called correcttermination).


3.6.3 Input impedance of open-line

We suppose I2p = 0 and Z2p = ∞. By inducting it into equations (3.38) and (3-41) weobtain

Z1p =A11

A21

=coshγ11Zc

sinhγ1= Zccothγ1. (3.52)

There is evident, that input impedance of open line Z1p will be related to frequencydependence Zc as well as to frequency dependence of cothγ. As we will see later, itwill be undulate around Zc curve just of value frequency dependence of cothghγ1 =cotgh(α+jβ)1 = Ctgejϕctg and will be decreased reciprocally to frequency. This situationis demonstrated in Fig. 3.5, where hyperbolic functions are performed as function to a;then curves of phase angle (full lines). By increasing a it is valid:

cotghγ1 = cotgha = thga = 1 (3.53)

We are able to deduct of phase angle curves, that character of open line may becapacitive as well as inductive or purely real, resistive. The curve of Z1p is in principleimplicated by reflections of voltage and current waves at the terminating point of line, byaddition to basic waves.

3.6.4 Input impedance of short-line

For this case it is valid: Z2k = 0, U2k = 0. We use again equations (3-38) and (3-41),

Z1k =A12

A11

=U1k

I1k= Zctghγ1 (3.54)

The curve Z1k to frequency will depend on

tghγ = tgh(α+ jβ)l = TejϕT

The situation is analogous as by open and is line; there is demonstrated in Fig. 3.5(dot and dash). We obtain an important cognition, first of all from the point of view ofmeasurement, by multiplying (3-52) and (3-54):

Z1pZ1k = Z2c coshγltghγl

and subsequently

Zc =√Z1pZ1k. (3.55)

Characteristic impedance Zc is equal to geometric mean of input impedance of openline Z1p and input impedance of short cut line Z1k.


Figure 3.5: Functions of tghγ1 and cotghγ1 to a

This derived equation (3-55) is very suitable for calculation of Zc for these lines withoutpossibility of correct termination as well as for very short lines.


Dividing equations (3.52) by (3-54) we are able to determine equations for calculationof Zc a γ, if we are able to gain Z1p and Z1k; and further equations for gaining primaryparameters R, L, G and C. The ratio

Z1k

Z1p

=Zctghγl

Zc1

tghγl= tgh2γl (3.56)

and therefore

tghγ1 =

√Z1k

Z1p

.

Using (3.5) and (3.11) it is valid

γZc = R + jωLγ

Zc= G+ jωC (3.57)

3.6.5 Input impedance of line terminated by common impedance Z2 6= Zc

We are able to express input impedance using (3-48), of which both nominators anddenominator of which are divided by Zccoshγ1:

Z1 =Z2coshγl + Zcsinhγl

Zcsinhγ`+ Zccoshγl= Zc

Z2

Zc+ tghγl

1 + Z2

Zctghγl

. (3.58)

The ratio P = Z2/Zc = |P |ejϕP is possible to possess equal to hyperbolic tangent ofcomplex magnitude ψ therefore the equation (3-58) will be P = tghψ then the relationwill be adapted to:

Z1 = Zctgψ + tghγ1

1 + tghψtghγ1= Zctgh(γ1 + ψ). (3.59)

Equalising equation (3.59) with the other one (3-54) for input shortcut impedancewe can judge, that these equations are analogue differing only by magnitude of complexargument. Therefore reflected voltage and current waves are rising at the line termination.These waves inflict undulation of input impedance to frequency curve. Reflections don‘trise at the terminations only, but in practice by real lines on non-homogeneities alongside.Then irregular undulation of input impedance characteristic Z1 is inflicted. Reflectionswill be equal to a size of non-homogeneity magnitude as well as so near to the beginningof line non- homogeneity is. Reflections inflict stability of circuits, crosstalks and doublecontours (so called spirits) especially by video transmissions.


3.7 Lines practically infinite

As we will be able to show, infinite line cannot be infinitely long 1 = ∞; the characterof infinite line, by another words such a situation, when no reflected voltage and currentwave are present, is becoming from certain value of attenuation, or loss. Let us definewhen the line will seem to be infinite, by what length expressed in Np or dB. Let usstart from knowledge of infinite line, of which input impedance Zc is by any termination,including open line or shortcut, (worst cases). Then it is valid:

Z1p = Z1k = Zc

As to (3.52) and (3.54) it is valid

Z1p = Zccothγl

z1k = Zctghγl,

then searched case of infinite line becomes, when

cotghγl = tghγl = 1,

This case becomes real, as it is demonstrated in Fig. 3.5. Expressed numerically it isread from tables

a = α1 = 3, 0Np.

(By a a = 3, 0Np je tgh = 0, 995; cotgha = 1, 005).

We can consider the line of loss 3,0 Np or larger as practically infinite. Eventhe rough faults at the end of line do not inflict any remark on the beginning of line.

3.8 Electrically short lines

Next chapter is devoted to electrically short lines. Only primary constants R, L, C, Gwill be efficient and therefore the open line will be performed as capacity, shortcut line asinductivity. In contrary to electrically long or infinite lines, where primary constants donot apply themselves separately (There are not measurable directly),only cumulatively assecondary parameters Zcaγ. For input impedance of open line is valid using (3.52)

Z1p = Zccothγl

If γl becomes so small, that

cotghl =1

γl


then Z1p will be changed:

Z1P = Zc1

γl=

√R+jωLG+jωC√

(R + jωL)(G+ jωC)l=

1

(G+ jωC)l. (3.60)

As it is clear from (3.60), electrically short open line performs itself as a capacitorwith losses and its capacity and leakage are proportional to length l. Thisknowledge is utilisable for fault location of interrupted wires. Analogically for line offinite length and input impedance of shortcut line it is valid (see 3-54)

Z1k = Zctghγl

If l becomes again so small, that

tghγl = 1

will be changed from Z1k to:

Z1k = Zcγl =

√R + jωL

G+ jωC

√(R + jωL)(G+ jωC)l = (R + jωL)l (3.61)

Electrically short shortcut line performs its inductivity with losses, proportional tothe length of line l.

The table of tghx informs us, that

tghγl = tghαl = αl

for

tghαl ≤ 0, 15Np.

The conclusion: Lengths of lines may not be related to km (in accordance to ourthoughts), but there is necessary to relate them to the values of loss. Appeared to thewidth of utilised band, one line is able to perform attributes of line electrically short, longand infinite also. The division of frequency areas, where the line performs variably is inFig. 3.6

3.9 Frequency dependencies of primary and secondary parame-ters of various line types

Real frequency dependencies of primary and secondary parameters will be performedin this chapter. There is necessary to realise consequence with relations for primaryparameters analysing them.


Figure 3.6: Various characters of lines

3.9.1 Air lines

Dependence curves of R, L, C and G on frequency are demonstrated in Fig. 3.7. Thereis evident, that deviations will be dependent on wire diameters, material, etc. Leakageis changing significantly to weather; G curve will be extremely increasing during iceaccretion, while it will be gradual by dry weather.

Figure 3.7: Frequency relation to primary parameters of air lines


Dependence of average loss and phase shift is in Fig. 3.8. The value of attenuation isα · `. There is important for suitability of line for telephone current transmission.

If αl = 1 the transmission is excellent,αl = 2 the transmission is good,αl = 3 transmission is sufficient,αl = 4 transmission is adequate.

For α1 ≤ 4, 8 understanding could be considered as possible.

Figure 3.8: Dependence of specific loss and shift on fair lines

Specific loss α is possible to determine from the equation for γ. There is valid

γ = α+ jβ =√

(R + jωL)(G+ jωC)

For

|γ| =√α2 + β2 = 4

√(R2 + ω2L2)(G2 + ω2C2)

and

α2 + β2 =√

(R2 + ω2L2)(G2 + ω2C2) (3.62)

Let be

γ2 = (α+ jβ)2 = α2 + 2jαβ − β2 = RG+ jωRC + jωLG− ω2LC

of its real component

α2 − β2 = RG− ω2LC (3.63)

We obtain adding equations (3.62) and (3.63)

α =

√1

2[(

√(R2 + ω2L2))(G2 + ω2C2) + (RG− ω2LC)] (3.64)


Analogically by subtract of equations

β =

√1

2[(

√(R2 + ω2L2))(G2 + ω2C2)− (RG− ω2LC)] (3.65)

There is possible to simplify relation for α due to practical applications supposing wireof larger diameter and for air lines by low frequencies, when we can consider

G ωC a R ωL (3.66)

There is valid as follows

γ = α+ jβ =√

(R + jωL)(G+ jωC) =

=

√jωL(

R

jωL+ 1)jωC(

G

jωC+ 1) =

=

√−ω2LC(

R

jωL+ 1)(

G

jωC+ 1) =

= jω√LC

√(1 +

R

jωL)(1 +

G

jωC) =

= jω√LC

√1− RG

ω2LC+

1

jω(R

L+G

C)

We can neglect second term under square root, evolve rest of equation into Taylorseries and neglect superior terms of it; then

γ = jω√LC[1− j

1

2ω(R

L+G

C)]

by next conversion

γ = jω√LC + [

√LC

2(R

L+G

C)]

By comparison Re and Im component we obtain for

α =R

2

√C

L+G

2

√L

C= αR + αG (3.67)

and

β = ω√LC (3.68)

The influence of leakage in low dry weather; then we can neglect second term in form(3-67). The influence of leakage on attenuation is evident from Fig. 3.9.


Figure 3.9: Attenuation of air line (bronz 3 mm)

We can consider in case of line for LF

ωL R a G ωC (3.69)

Equations (3.64) and (3.65) will be transformed into another form

α =

√0 +

1

2

√R2ω2C2 =

√ωRC

2(3.70)

and

β =

√ωRC

2(3.71)

There is to consider significant dependence on temperature; therefore automatic reg-ulation is introduced by long-hauled lines. Characteristic impedance of air lines is tobe designated from wellknown form

Zc =

√R + jωL

G+ jωC

or it is evident, that impedance depends on primary parameters. In case of LR lines,conditioned by (3-69) it is valid

Zcnf =

√R

jωC=

√R

2ωC− j

√R

2ωC(3.72)


Figure 3.10: Impedance of air and cable lines depending on frequency

and there is evident, that impedance composes itself as of Re a lm components.Values R, G are against ωL and ωC negligible by condition (3-66), therefore

Zcvf =

√L

C(3.73)

Characteristic curve is imaged in Fig.3.10. There is imaged also curve of cable line forcomparison. Suppose as the last f = 0, then these forms will be changed into

α =√RG, β = 0 (3.74)

and

Zc =

√R

G(3.75)

3.9.2 Cable lines

If we will keep original division of cable lines, let us keep our attention to LF non-coiledlines. The capacity C and inductivity L are independent of frequency. We can consider


Figure 3.11: Frequency dependency α, β and Zc for couple types of coiled lines

resistance R and leakage G as also constant in this frequency band; there are significantlydependent on temperature. Attenuation α is to be calculated of this form

α =

√ωRC

2(3.76)


And corresponding curve is imaged in Fig. 3.11. Analogically specific shift

β =

√ωRC

2

We can consider only resistance in numerator and component with capacity denomi-nator. (Analogical with see Air lines LF) and so we obtain simplified form

Zcnf =

√R

jωC=

√R

2πfce−45 (3.77)

Demonstration of the curve is in Fig. 3.10. Impedance is decreasing to increasing fre-quency. For frequencies of the order 100 kHz the imaginary component approaches zeroand real component will be stabilised around 100 Ω. The impedance of most ordinarycables used in local or access networks of diameter 0,8 mm is around 600 Ω by frequency of800 Hz. This value was chosen as terminating impedance for all LF transmission equip-ment. As to decreasing impedance to frequency is in the beginning of telephone bandmismatching of plus 400 Ω(by 300 Hz) and at the upper end of band (3400 Hz) reversedcase cca minus 300 Ω. Despite this fact these mismatching are not inflicting the qualityof transmission in access networks. Coiled lines decrease attenuation by LF transmissionas we know. This is provided by insertion of Pupin‘s coils into cable. Therefore the in-ductivity of cable line is increased. Substitutional scheme of line could not be consideredin simplified form as by uncoiled line. There is necessary to consider all primary magni-tudes. Coiled line is composed of series π-piles, of low pass character. Limiting frequencyis possessed by form ω0

Je dn vrazem

ω0Ls =1

ω0Cs(3.78)

where Ls is inductivity corresponding to one coiling section

Ls = Ls+ Lp = (L+Lps

)s. (3.79)

where L is specific inductivity of line [H/km], Lp is inductivity of Pupin‘s coils [H], sso called coiling step [m] (called also pupinising step).

Capacity Cs is given

Cs = Cs

4. (3.80)

Inducting to (3-79)

ω0(L+Lps

)s =1

ω0Cs4

, (3.81)


Figure 3.12: Relation of specific attenuation to frequency α

and transforming

ω0 =2

s√C(L+ Lp

s), (3.82)

fo =1

πs√C(L+ Lp

s)

(3.83)

Attenuation and impedance rise to extreme values by this frequency. Therefore theeffectively transmitted band is limited by 0,75 f0.

Specific attenuation is to be calculated by following form

α = [R + Rp

s

2

√Cs

Ls+ Lp+G

2

√Ls+ LpCs

]1√

1− ( ωω0

)2(3.84)

and characteristic impedance

Zc =

√LpkCs

1√1− ( ω

ω0)2

(3.85)

where

Lpk =1

f 20π

2sC(3.86)


is inductivity of coiled pair.

Transmitting attributes of coiled lines are synoptically imaged in Fig. 3.11. There isevident of before presented figures, that attenuation is by coiling

• decreasing, and so more intensively in accordance to increasing inductivity (so calledlight or heavy coiling),

• attenuation is in major part of band almost independent of frequency,

• increasing inductivity inflicts significant narrowing of transmitted band.

There is evident of relation for specific phase shift β, that

• it significantly increases with increase of inductivity itself and it is closely tied withdecreasing of phase as well as group velocity.

There is evident from impedance characteristics, that impedance itself

• increase ReZc with heavier coiling (disadvantage),

• increase (significantly) in range close to limiting frequency (significant disadvan-tage),

• imaginary component is approaching to zero (advantage),

• by limiting frequency also increase (disadvantage).

We are able to say overall, that main effect of coiling is in decrease of attenuation infrequency range of telephone voice band (accordingly to UIT 300-3400 Hz), which wasextraordinary important on the eve of telephony, while by decreasing of attenuation wasreached increase of telephone link. Also the reach of such attributes, which are accessibleby higher frequencies (over 30 kHz), i.e. characteristic impedance is approximately realand constant, phase shift is linear and also phase and group velocity of propagation areroughly constant. On the other hand narrowing of band is disadvantageous. (There wasdone so called decoiling, i.e. in order displacing of inductivity units in order of introductionof HF analogous or digital multiplexes), increase of ReZc and decrease of vf and vs.

Actually the importance of coiling is decreasing due to the fact, that it is a significantbar of broadband services. It survives

• by short trunk (former node) cables,

• by LF analogue radio transmissions.


Table 3.1: Types of coiled lines and their attributes

Inductivity Impedance Specific attenuation Limiting BandwidthPup.cvek by 800 Hz 10−3 dB/km frequency

mH W 800 Hz 3,4 kHz kHz kHzK 177 1590 188 - 2,9 0,3 - 2,17F 63 740 198 300 3,6 0,3 - 2,7K 88 1120 236 274 4,1 0,3 - 3,06F 36 560 233 246 5 0,3 - 3,75K 70 990 277 290 4,5 0,3 - 3,4F 30 520 246 266 5,5 0,3 - 4,1

The usage of LF coiled cable lines has been till the intensive avalanche of broadbandservices operated as the simplest, cheapest and low cost solution, first of all for shortdistances. Let us conclude with some typical parameters of coilings used in CZ. Thelength of coiling step 1830 m, inductivity of coiling unit 88/36 mH, wire diameter 0,9 Cu.

Note: The very last concept of high quality of Hi-Fi audio transmissions was developedin seventies of last century with inductivity of coiling units 3,2 mH, and halved coilingstep to 915 m, which enables transmission up to 15 000 Hz.

Symmetrical HF cables

Basic information about these cables were mentioned before. There was introducedthe relation for attenuation (2-19), characteristics of which depending to frequency isimaged in Fig. 3.12. Specific attenuation. It increases quasilinear by this type of cable,meanwhile for cables with 0,9 mm Cu diameter the function is curved. Growth of α isinflicted by parameters R and G, while C and L are quasi independent of f . Dependenceβ = ϕ(f) for the same type of cable is performed in Fig.3.13. This dependence is linearand calculation is to be done by form used for calculation

β = ω√CL (3.87)

For this case both vf as well as vs are constant.There are drawn ReZc = ψ(f) and ImZc = ξ(f) in Fig. 3.14. As it is evident

from this figure, ReZc is quasi constant approximately from 30 kHz (being insulated bypaper-air cca 150 Ω, by styroflex-air - cca 170 Ω and ImZ is slightly capacitive). As itis evident from before mentioned figures, transmission parameters of HF cables are veryadvantageous in range of carrier frequencies (α,Zc).

Coaxial cables

Basic equations for calculation of primary parameters were introduced in chapter2.3.2.4. We are able to demonstrate their frequency dependence in Fig. 3.15. We canconsider corresponding secondary parameters in simplified form for HF cables, for coaxialcables from f ≥ 60kHz60 kHz, then


Figure 3.13: Dependence of specific shift β on frequency

Figure 3.14: Dependence of ReZc and ImZc on frequency


Figure 3.15: Frequency dependency of coaxial cable primary parameters is real (Zc.=

75 Ω)

R ωL a G ωC

then

α.=R

2

√C

L+G

2

√L

C(3.88)

(second component is negligible)

β.= ω

√CL (3.89)

and

Zc.=L

C(3.90)

Curves of α and β are imaged in Fig. 3.16. Dependence of Zc = ϕ(f) is then in Fig.3.17. As it is evident, the dependencies as β as Zc are advantageous from the point ofview of transmission. Linear dependence of specific phase shift β corresponds to constantsvf and vs (excluding beginning of range). For vf it is valid

vf =ω

α=

1√LC

(3.91)

It could be proved, that in vf range is constant phase velocity and that it is equal tothe quoting of light velocity to square root of dielectric constant εr.


Figure 3.16: Frequency dependencies α and β of coaxial and cable - 1,2/4,4 (little),2,6/9,4(medium)

Figure 3.17: Frequency dependencies Zc = ϕ(f) for little and medium coaxial pairs

3.10 Homogenous line by high frequencies

Let us remark some questions concerning of extremely broad bands in conclusion of thirdchapter. As it was introduced in chapter 3.9, we obtain for this frequency range forms for


Figure 3.18: Circumstances in extra high voltage by HF current transmission

Zc =

√R + jωL

G+ jωC

and

γ =√

(R + jωL)(G+ jωC)

could be simplified fulfilling conditions R ωL and G ωC. Then we obtain

Zc.=

√L

C

γ.= jω

√CL

.= jβ (3.92)

and

β.= ω

√CL, α

.= 0 (3.93)

As it is evident from relation (3.94), these considerations are solved simplified forHF lossless line. From the form for Zc it is clear, that homogeneous line has by HFcharacteristic impedance constant and withal real (see curve in Fig. 3.17).

3.10.1 HF open line

There will be described often case in telecommunication practice, HF links upon extrahigh voltage line. HF equipment are connected to EHV line through coupling capacitorsVK. Example of two layer network is imaged in Fig. 3.18. Suppressors Tl are barring to


enter of HF currents into EHV equipment. There are taps coupled to transformers TS.These taps are to be considered by HF as sections of open line. By defined, so calledcritical lengths of these taps HF shortcuts are becoming and there is necessary to preventthem by design.

Similar case becomes by HF distribution of modulation for wired radio. There areinstalled taps in these points (communities) to receivers of audio modulation (see Fig.3.19). They perform also taps with possibly critical length, which we try to investigate.Outgoing of n known circumstances at far end of line, when Z2p = ∞, I2p = 0 and U2p isof certain amplitude. We use equations (3.7) and (3.12), where integrating constants A1,A2 will be defined according to (3.15) and (3.16). We obtain by induction:

Uy = coshγyU2 + ZcsinhγzI2 (3.94)

and

Iy =1

ZcsinhyU2 + coshγyI2 (3.95)

There is apparent, that y performs the distance off far end, Uy and Iy, are voltage andcurrent in this point y, distanced y[km] from far end of line. (Note: there is analogy toequations (3.38) and (3.39)).

Figure 3.19: Conditions for modulation of wire radio transmission

Let us study voltage and current circumstances alongside HF open line:a) Voltage circumstances: We induct I2p = 0 into I2 in equation (3.95) and we

obtain (using 3.93)

Uyp = U2pcoshγy = U2pcoshjβy (3.96)

There is valid:

coshjβy = cosβy, kde β =2π

λ

andU2p may be written in following form:


U2p = |U2p|ejωt

then

Uyp = (|U2p|cos2πy

λ)ejωt = |Uyp|ejωt (3.97)

Part of form in brackets is absolute magnitude and the rest in form performs phase.There is evident, that absolute magnitude is depending on distance off far end y andis changing to function cosine. There will be points alongside the line, where 2π

λy=0,

therefore voltage Uyp will be permanently zero and further points, where cos2πλy reaches

its maximum - minimum (1,−1). As it is evident of (3-98), phase will be independent ofy. We can state, that in HF open line emerge standing waves expressed by equation(3-98). Investigating limited form for

y = 0 je cos 2πλy = 1, y = λ

4je cos2π

λy = cos π

2= 0, y = λ

2je cos 2π

λ= cos π = −1 etc.

b) We will induct current relations into equation (3-96) for I2 = I2p = 0 and obtain:

Iyp =1

ZcsinhγyU2p (3.98)

Inducting

sinhγy = sinhjβy = jsinβy = sin(sinβy)ejπ2 = (sin

2πy

λ)ej

π2

and

U2p = |U2p|ejωt

We obtain

Iyp = (|U2p|Zc

sin2π

λy)ej(ωt+

π2) = |Iyp|ej(ωt+

π2) (3.99)

The form performs standing wave of current, where first part means again variableabsolute magnitude, depending on y as per function sine. Second part performs phase,which is turned by π

2, see Fig. 3.20. There is evident of this figure, that maximums and

minimums Uyp and Iyp are alternating. This is displayed in Fig. 3.20.c) Voltage and current at near end of line: We obtain corresponding forms

inducting variable length l, instead of y into forms (3.95) and (3.96). In case of long line:

l =λ

4+ kλ

eventually

l =3

4λ+ kλ kde k = 0, 1, 2, . . . ,


Figure 3.20: Standing wave of voltage and current of open HF line

will be

U1p = 0, I1p = ±U2p

Zce(jωt+

π2)

d) input impedance of open line will be determined from equation (3-52)

Z1p = Zccothγ1 = Zccoshγ1

sinhγ1

and as per

coshγl = coshjβl = cosβl = cos2π

λl, sinhγl = sinhβl = sinβl = jsin

2π

λl

therefore

Z1p = −jZccotgh2π

λl. (3.100)

The verity is clear from this form, that input impedance of HF open line is purelyimaginary (capacitive or inductive), even if characteristic impedance Zc is purely real.Figuring out of the form 2π

λfor various l and by multiplying Zc it is possible to gain

diagram in Fig. 3.21. There is evident, that for 1 = 0 to 1 = λ4

is Z1p capacitive. Forcase 1 = λ

4emerges HF shortcut of line, which is acting as serial oscillating circuit. For

1 = λ4

to 1 = λ2

is Z1p inductive. Finally for 1 = λ2

the behaviour of the line is equal toparallel coupling of LC. For case of line length λ/4 are inflicted dangerous HF shortcuts,as it was introduced in the beginning of this subchapter. Four wave line is utilisable inpractice as a feeder of aerials in the role of band pass (suppressor of harmonics - see Fig.3.22).


Figure 3.21: Dependence of Z1p for various lengths of HF open line

Figure 3.22: Standing wave of voltage and current of open HF line

3.10.2 HF shortcut line

Analogical procedure as in case of open line is possible to derive following forms:

Uyk = (|I2k|Zcsin2π

λ)ej(ωt+

π2) (3.101)


and

Iyk = (|I2|cos2π

λ)ejωt (3.102)

The results are standing waves of voltages and currents, plane of voltage and currentvectors is again turned over π/2. Input impedance Z1k is to calculate as per (3.54)

Z1k = Zctghγ1 = jZctg2

λ1 (3.103)

The curve of Z1k depending on 1 is dual case to dependence of before presented foropen line. For case 1 = λ

4comes into being important situation, when characteristics of

line reaches infinite magnitude of impedance. There is possible to utilise this attribute inpractise as band stop of aerial feeders (see Fig. 3.23). Band stop is able to shortcut allharmonics and performs impedance for transmitted frequency.

Figure 3.23: Four wave band pass

Figure 3.24: Quarter wave band stop

Next possibility of use is drawn from assumption, that we will provide taps λ/4 bi-laterally and continuously, and so we reach the principle of waveguide - see Fig. 3.24.Concluding third chapter we traversed conclusions of theory homogeneous lines importantfor construction of cables and lines.


Figure 3.25: Waveguide principle

3.11 Examples

A) There was measured voltage in the beginning of line (near end) U1 = 60 V, impedanceZ1 = 600 Ω. The current at the far end was measured I2 = 10mA. Calculate at-tenuation in NP and dB.

B) There are given primary parameters of line valuedR = 42, 2Ω/km,L = 8, 96mH/km,C = 6, 32µF/km, G = 0, 7.10−6S/km. Calculate Zc a γ0 by frequency f = 800Hz.

4 Types of metallic lines and cables

4.1 Open air lines

Open air lines utilise masts, consoles and insulators. There were exploited very inten-sively during last century, first of all due to their excellent transmitting features. Theyperformed the backbone of trunk links. Difficult assembling in cities, dependence onweather conditions, (glace) led to their abandon. First cables into metropolitan networkswere built up around the year 1900, first long hauled cable, the section Praha - Koln- Jihlava - Brno - Wien/Bratislava in 1925. Masts equipped by concrete poles are nowexploited for hanged (catenary) cables in access networks, metallic as well as fibre optics.

4.2 Cable lines

Cable lines were differed in accordance with standards (SN 34 7831 a SN 34 7851) into”Telecommunication local cables” with wire 0,4; 0,6; 0,8 mm and ”Telecommunicationlong hauled cables” 0,9; 1,3 mm. Other differentiation is from the point of view usedfrequencies - LF and HF cables, for data transmission, structured etc. Further division is


possible according to type of laying as cables free laid, tracked (into before built ducts),hanged cables, submarine, etc.

As to actual technical and technological developments there are mutual mixture of allfeatures mentioned before. Long haul cables and node cables are entering access networks,etc.

Telecommunication cables are composed by cable core and protective coating. Ca-ble core is a system of units, into positions (layers) contradirectively screwed, (twisted)- eventually screwed in groups - with inlets, fillers and diameter insulation. Basic con-struction elements are pairs, it means two wire conductors twisted together by certainlength of screw. Wires (even pairs) are twisted further into quads by quad cables.

We recognise cross quads, where all four wires are twisted together. Wires aredenoted a-b, c-d in such a way, that opposite ones serve for basic circuit (trunk) see Fig.4.1.b. They are described as X quad. Quads DM (Dieselhorst - Martin) are composed insuch a way, that both pairs are twisted individually first with differed winding of lengthl1 and l2 and finally in second step are both pairs twisted by third length of twisting l3 inreversed direction. - see Fig. 4.1.a.

Figure 4.1: Construction of a) DM quad, b) cross quad

Protective coating saves cable core against mechanical damage, humidity, distur-bances of higher voltages, electrical traction systems, etc. Protective coating is composedof several layers in accordance with the type and designation of cable.

We can introduce following case as an example of construction, when cable core iscovered by insulating paper layers with upper coat by stamped lead. This type withnaked lead coat are used as tracked cables used in ducts. Protection against other dangers(corrosion, electromagnetic induction, mechanical damage or fire) are provided by otherspecial coating layers, as armouring e.g.

Laid cables are designated for direct laying into soil, are armoured by steel belts andby other protective coats. The following example of other protection over lead coat couldbe such a so called pad

• bitumen

• impregnated paper

• bitumen

• jute


• bitumen

armour - steel belts - binded

• bitumen

• jute (twines of polypropylene)

• bitumen

• paintwork by calcareous milk

Protection of cable core may be provided also by other means, as for example lead forcoat could be by aluminium. Such a coating is suitable for protection against inducedvoltages. Polythene and polyvinylchloride (PVC) sandwiched by aluminium for uppercoating is used for corrosive environment. Cables for river crossing are equipped bywired armour against strong track. Also are used so called whole plastic cables.

Conductors

The most utilised as well as best material for cable conductors (wires, coaxial pairs) ispure electrolytic copper. Diameters of these wires differ from 0,32 up to 0,8 mm for localcables, from 0,9 up to 1,4 mm for long haul symmetric cables. Chose of wire diameterdepends on length of link, attenuation and features of transmitted signal. As to the factof permanent shortage of copper in world trade, there were various seeking to spare itby decreasing of used diameters (as to above mentioned 0,32 mm - 0,5 mm). There wereprovided also attempts to replace copper by aluminium with varying success. First ofall during VW II in Germany as well as in former CS till 1965. Needed diameter ofaluminium wire is to be calculated by:√

%Al%Cu

=0, 0299

0, 0175= 1, 3

This replacement leads to larger diameters of cables at all, also material consump-tion is increasing. Aluminium is worse from the point of view of mechanical strength.There are used its compositions as VK 33E (composition of Al, Fe, Mg, and Si). Thesecompositions are better as to the before mention strength, better electrical parameters,better homogeneity of wire. Though all of above mentioned measures there is necessaryto provide additional compensations.

Insulation of wires

Insulation paper - air. Wires of local cables are twined by one or two layers ofpaper band. By long-haul cables it is necessary to increase share of air layer by twinedcord. (generally known as kordel) under paper bands. This technology enables decreasingof functional capacity and due to this fact the attenuation is better. This technology isutilisable up to 250 kHz.

Insulation styroflex - air is used first of all by HF- up to 560 kHz for their betterattributes.


Figure 4.2: Wrapping of wire by cord

Insulation by high-pressure polythene is provided by local cables (whole plasticcables), where wires are insulated by continuous layer of high-pressure polythene sized0,2 to 0,4 mm. The advantage of this technology is, that humidity penetrates into cablevery slowly.

Cable profiles

Cable core itself is spliced by splicing machines. Each upper layer obtains 5 to 10 units(pairs or quads more). There are performed tables, where numbers of units are calculatedfor various types of cables, as 1, 6, 12, 18, 24 e.g. Series of DM cables with 0,9 mm wires(number of quads in individual layers) is: 5, 8, 12, 19, 27, 37, 48, 61, 90.

Example of cable profile LF 27x4x0,9 DM - (DCKQYSE) is performed in Fig. 4.3.

Figure 4.3: Profile of cable

Constructing units in cable core need not be equal as by LF cable, where could bepossessed several audio shielded pairs in his centre. Audio pair RP is composed of twotwisted wires, twined by one to two paper bands and more by one metal plated paperband (shielding), which decreases penetration of disturbing voltages into these pairs.

Example: 3x1,3 RP + 61x4x 0,9 DM - profile of 3 audio shielded pairs Ø1,3 and 61quads DM Ø0,9.


Local cables are only seldom of combined profile; number of units may be very large.Typical series are: 5, 10 15, 20, 30, 40, 50, 60, 70, 100, 150, 200, 300, 400, 500, 600,800, 1000, 1200, 1800, 2000 (in pairs). Splicing in concentric position is provided onlyby little number of pairs; the profile by larger numbers (over 100 pairs) is composed ofbefore twined groups of units (pairs or quads).

Each group is twined separately; several created groups is again taped into final cablecore. Individual groups are transformed by final taping from radial profile into half orquarter radial or segment as it is performed in Fig. 4.4. The advantage is in economicalproduction and easier transfer of individual groups from one into other cables by branchsplicing (cabling of exchange area).

Figure 4.4: Composition of elements into cable profile

Cable coats and their protectionOlder cables for both trunk as well as local networks were coated exclusively by lead.

The lead as an classical material has suitable features, as flexibility, strength, resistanceagainst corrosion by water, etc. Seen by replacement of lead (shortage, expenses) wasresearched applicability of aluminium, plastics as well as steel for above mentioned pur-poses.

Aluminium coated cables are more suitable in seldom point of view as low weight,better reduction factor. On the other hand disadvantages especially by low mechanicalflexibility, difficult splicing and soldering bring other hardly solvable problems.

All plastic cables mainly using HDPE and PVC presents good forming ability, suf-ficient stability as well as corrosion resistibility. Long term infliction of humidity doesnot bar certain infiltration of water vapour into cable core. Upgrade of this constructionwas done by such a measure, as covering of cable core by aluminium folio formed intotube longitudinally seamed and secondly is suppressed final coat from polythene (so calledlayered coats). Actually are used numerous new, modern sophisticated production meth-ods as filling of cable core by lubricators. These lubricants upgrade protection againstlongitudinal infiltration of humidity.

Groundstones of cable production. Processes of cable production are differedinto main operations, auxiliary operations and supervision. Auxiliary operation is e.g.preparation of copper wire (staining, calibrating), insulating paper, preparation of Pband Al composition (melting) and preparation of armouring (cutting and impregnation of


paper, winding and impregnation of polythene band, impregnation of jute, polypropylenetwines, asphalt glazing).

Main operations compose of:

• tracking of copper wires,

• annealing of copper wires (upgrade of flexibility)

• insulating of copper wires,

• completing of wires into units,

• completing of cable cores,

• drying of cable cores,

• coating of cable cores,

• armouring,

• final quality supervision.

Permanent particular supervisions are provided among individual production phases.Cable is produced in manufacturing lengths of 200 to 500 m, is winded onto trans-

porting drum and beginning as well as end are pointed. Individual manufacturing lengthsare composed alongside cable trace.

Signing of cablesIn accordance with cable signing we are able to recognise material of wires, insulation

type of wires, core and coat, type of coat protection, nominal number of units, type ofcomposition as well as measures of wires or coaxial tubes. The base of font signing per-forms create sign for type of cable. We are able to meet such types of telecommunicationcables:

TK - telecommunication cable localDK - telecommunication cable long haulRK - audio transmission cableNK - signalling cableSK - telecommunication cable indoorBasic symbol TK is used for local telecommunication cables. (as to older signing

”telephone cable”). We insert other symbols behind character T, there are denotingmaterial of wires:

C - copperA - aluminiumJ - composition of aluminium (VK 33E)Next character points type of wire insulation:Y - polyvinylchloride (PVC)E - polythene (PE)G - rubber


B - balloon polythene insulationIn case of absence of this character, there is paper - air insulation used. Symbol for

coating material is inserted behind character K:O - leadQ - doped lead (for tracked cables for ducts)A - aluminiumY - PVC - polyvinylchlorideE - PE - polytheneCharacter F means for some cables, particularly indoor, shielding foil. All plastic

telecommunication cables, where this shielding is obvious this sign is absent.Next characters define type of coat protection:V - staple covering Y - passive anticorrosive protection of PVC (formerly type 0K3)

B - anticorrosive bind protection of PVC (formerly type 0K2) P - armour of steel bandsD - armour of steel wires R - reinforced armour of steel wires including pad (river cabletype) Z - armour of aluminium wires

Behind character notation is prepared entry denoting number of units, type of design(paired by character P, crossed for LF operation by characters XN) and diameter of wiresin mm.

Example of cable signing: TCEKEZE 50 P 0,5 - telecommunications cable local(TK) with copper wires (C), polythene insulation of wires (E), coated by polythene (E),armoured by aluminium wires (Z) and protective cover of polythene (E). 50 pairs (50 P)a nominal diameter of wires 0,5 mm.

Signing of wires, pairs and quadsThere are used coloured press for recognising of individual wires in units in such a

way:

• wire a dense printing of blue traverse strip

• wire b scarse printing of blue traverse strip

• wire d dense printing of red traverse strip

• wire d scarse printing of red traverse strip

Single units (pairs, quads) one from other are to be recognised by colour of markingfile. Red file marks so called counting unit and neighbouring green file directive unit.Numbering of units is launched from counting unit in direction of directive unit. Allresting units are marked by blue files (odd units) and white (even units).

Node (long haul) cables use another recognition of units in cable core. Whole quadis coloured by same colour and single wires differ by number of coloured stripes (1 to 4).Neighbouring units differs by colour of stripes: red and blue are alternating.

Signing

• wire a continuous printing of one traverse strip

• wire b continuous printing of two traverse stripes


• wire c continuous printing of three traverse stripes

• wire d continuous printing of two traverse stripes

Accessories of telecommunications cables - Accessories are used for splicing,branching and termination of cables.

We rank here: Cable splices are used for splicing of cable manufacturing lengths.Branching splices and cable heads for termination of cables in buildings or cabinets.

Cable laying of open laid cables is provided by one or more cables into dug out cablegroove. Cables are laid manually or by special cable layers. Depth of groove could befrom 0.5 to 1 m (urban - outer urban area). Cable should be covered by protective bricksor concrete tables as well as by coloured signal strap (orange for telecommunications,blue for railway, red for power supply). This is useful by sudden digging works by othersubjects or also by targeted searching for one laid cable. Trace appointed by design shouldbe as far as short, kept away water streams, railways and main roads. In case of extremeneed for telecommunication services and supposed demand for increasing capacity, first ofall close to exchanges are built ducts. Originally concrete blocks with tubes inside werereplaced by construction of plastic tubes. Both are settled as neighbouring and in layerstoo. Plastic tubes exclude problems with alkaline character of humid concrete, which isable to inflict corrosive impacts. Splicing is provided by special mechanical splices usingsplicing machines. (3M, Belden, AMP Picabond etc.).

4.3 Electrical attributes of metallic lines

A. Air lineBasic magnitudes influencing decisively transmission of air lines are real resistance,

insulating resistance, inductivity and capacity. Using these primary parameters it ispossible to derive next characteristic attributes of line as are its specific attenuation,phase shift, impedance, etc.

DC resistance of used wires is pointed as Ro. The DC value of resistance is increasedby transmission of alternative current up to Rf , where

Rf = Ro(0, 5d

√fµr%

+ 0, 2) [Ω/km], (4.1)

where d diameter of conductor [mm] f frequency [kHz] % specific resistance(Table), µr relative permeability (Cu and Al =1, Fe=140).

Increase of resistance to√f is parabolic. The equation is valid since critical frequency

fk, where

fk =4%

µrd2(4.2)

The resistance is increasing by squared dependence up this frequency up to the valueRf = 1, 25Ro


Inductance L of air lines is given by space arrangement of their line conductors.

L = 0, 4(ln2a

d+ 0, 25) [mH/km] (4.3)

wherea distance of wire axes [cm] d diameter of conductors [cm]

Factor 0,25 is negligible by higher frequenciesCapacitance C is to be calculated by relation

C =29εrln2a

d

[nF/km] (4.4)

where εr is 1, by ice glaze 1,6.Conductance G is

G = Go + v.f [µS/km] (4.5)

Derived from theory the specific attenuation where Go is insulating conductance byDC, it seems to be 0,1 S/km by dry weather and 0,5 S/km,by dry weather, 0,25 by rainand 0,75 by ice glaze,

v conductance factor 0,05 S/kmf frequency [kHz].

α =Rf

2

√C

L+G

2

√L

C[Np/km] (4.6)

where all values are specific ones and are related to 1 km of line. The relation is validfirst of all for higher frequencies. For LF transmissions and for conductors with diameterd < 2mm is leakage component negligible and by condition ωL R is approximatelyvalid

α.=

√RωC

2[Np/km] (4.7)

For specific phase shiftit is valid

β = ω√LC

ωL R and low frequencies

β =

√ωRC

2[rad/km] (4.8)

Characteristic impedance for high frequencies

Zc.=

√L

C[Ω] (4.9)


and for low frequencies

Zc.=

√L

ωC[Ω] (4.10)

B. Electrical attributes of cable lines

Resistance of symmetric cable circuit is

R = Rokf = Ro(kskbko) [Ω/km] (4.11)

Where Ro is loop resistance, measured by DC [Ω/km]ks factor of surface increase by surface effect,kb factor of resistance increase by proximity effect,ko factor of resistance increase by surrounded conductors (shielding, coating etc.).Factor ks is calculated from change of critical frequency (by diameter of wire 0,5 mm,

fk = 280kHz; by diameter fk = 42kHz).For supercritical frequency

ks = 0, 12d√f + 0, 25

whered is diameter of wire [mm]f frequency [kHz]

For frequencies lower of critical one it is valid

ks = 1, 25(f

fk)2

Proximity factor of conductors kb seems to be 1,2 to 1,3 and neighbouring conductorseffect 1,20 to 1,10 in accordance of unit placement close to the coat of in the centre ofcable profile. Resulting effective resistance designates attenuation of cable circuit.

Specific capacity of cable pairs is

C =28εrlnpa

d

[nF/km] (4.12)

where εr is relative dielectric constant by cables insulated by paper - air seems to be1,5 to 1,8, by styroflex - air 1,3,

p type of unit factor, for quads DM it is 0,65, for quads X it is 0,75, for pairs P it is0,94,

a distance from wires [mm]d diameter of wire [mm]Capacity is almost independent of frequency and results by addition of several partial

capacities among wires. In compare with air lines this capacity by 5 -7 larger.


Inductance L is given by relation

L = 0, 4ln2a

d+ 0, 25 [mH/km] (4.13)

Inductance of cables is relatively smaller in compare with air lines. This reality influ-ences negatively to value of attenuation, as it will be explained as follows (coiled cables -artificial enlargement of L).

Conductance G is composed of two components. The conductance by DC voltagebetween Go, which seems to be by long haul cable 0,1 nS/km (corresponds to insulatingresistance 10000 MΩ/km), 0,2 nS/km (5000 MΩ/km) for local cables insulated by paper- air; for all plastic cables it seems to be larger. Second component of leakage by AC isindicated as ratio to conductivity of operational capacity, thus.

Gf = kgωCp (4.14)

conductance factor kg for low frequencies is 0, 55.10−3, the influence of AC in comparewith conductivity is small. By high frequencies increase magnitude of AC leakage factor to1, 2.10−3 by 10 kHz and up to 7.10−3 by 100 kHz. Using polythene or styroflex insulationkg factor decreases by two orders.

Specific resistance is to be calculated by form

α =

√RωC

2[Np/km] (4.15)

Respecting enlarged capacity of cable lines the attenuation related to frequency of au-dio telephone range (300-3400 Hz) by non-coiled lines rapidly by parabola. This distortionof attenuation is to be respected by design.

Impedance is to be designated by equation

Z =

√R

jωC[Ω] (4.16)

4.4 Coiled cables

Coiled cables - based on principle of so-called pupinisation (inventor M. I. Pupin) utiliseartificial enlargement of cable lines inductivity. The decrease of line attenuation in limitedfrequency range is enabled as well as decreasing of attenuation characteristics distortion.Inductive coils are inserted into cable along regular distant steps - see Fig. 4.5. Thedistance of coils is so called coiling step s. The strain section, it means first section of thefrom cable head is ever

lnb. =s

2


Figure 4.5: Principle of coiled line

Reasons: There are interconnected strain sections in amplifying station = s, bettercurve of Zc = ϕ(f)

(Note: Coiling is one of methods for artificial enlargement of line inductivity. There isthe most exploited method. Except this one are known other methods, there are seldomused. For example so called krarupising (Krarup - Danish physics). It uses principle ofcopper wire binding by soft iron wire (complicated manufacturing), further method ofso-called bimetallic wire and wire with magneto dielectrics.)

Let us affirm decrease of attenuation by following consideration: For attenuation it isvalid:

α =R

2

√C

L+G

2

√L

C= αR + αG, (4.17)

whereαR is component of specific attenuation, derived from R,αG is component of specific attenuation, derived from G.Let us adapt relation 4.17 to

α =

√R2C

4L+

√G2L

4C

We point out from the first form

x =

√RC

GL

and from the second one

x−1 =

√GL

RC

We obtain

α =

√RC

GL

√RG

2+

√GL

RC

√RG

2. (4.18)


Denoting√RG = αo, we modify (4.18) into:

α =αo2x+

αo2x−1 = αR + αG (4.19)

We are able to draw graph α = f(x) - see Fig. 4.6. There is evident from this figure,that α has distinct minimum and it is reached by x = 1, when it is valid

R

L=G

C

As it is clear from the form

dα

dx= 0

Figure 4.6: Dependency of specific loss for coiled line on x

The form (4.19) is possible to adapt for practical usage to another form

α

αo=x

2+

1

2x. (4.20)

Drawing ααo

= f(x) we obtain the ”V” curve, as in Fig. 4.6 (for x = 1 is minimumααo

= 1). For x = 1 it is valid αR = αG and attenuation of cable is of the smallest value

αmin = αR + αG = αo =√RG


There is possible to learn from the dependence ααo

= f(x), that coiling is sensible forx 1. Decrease of attenuation is reachable by minimising

x =

√RC

GL

There is evident, that x is possible to diminish by

• reduction R, enlargement of wire diameter (impossible)

• reduction C, distance enlargement of conductors (impossible)

• enlargement G, (impossible!)

• enlargement L, the only real possibility

The appreciation of coiling suitability is possible to verify from primary parametersR, L, G, C by calculation x and if x 1 then also α

αo 1 and by coiling α is smaller,

that means suitable.Optimal value of inductivity is again derived from considerations and equals

Lopt =RC

G(4.21)

Inductivity is inserted into cable lines by coiling sections (s) and is denoted e.g.H- 88 - 36 where H means length of section 1830 m (2000 yards),B means section length 915 m (1000 y),88 inductivity of pair coil in mH,36 inductivity of phantom coil (see later) in mH.Note: 1) Denoting: 1700 - 30 - 12, is coiling of German origin, where 1700 is length

of coiling section in m, 30 and 12 are values in mH for pair and phantom circuits.Values of coil inductivity are different and they influence curve of α = ϕ(f). As it

is evident from the first touch, (see also Fig. 4.5), upper frequency margin is limited byinserting inductivities into lines - there is created in principle low pass filter (disadvantage).

Limiting frequency of pile is to be calculated

fm =318√LpCs

[kHz] (4.22)

whereLp is inductivity of coil [mH]C specific capacity of circuit [nF/km]s length of coiling section [km]

Impedance is given by relation

Zc =

√LpCs

[Ω] (4.23)


Figure 4.7: Method of phantom and superphantom composition

Phantom circuit is created to upgrade exploiting of line. There is utilised fact, thatalong two pairs of one quad is third LF connection realisable. (Fig. 4.7). The principleis in division of currents of compound circuit (other term for phantom) into a, b wires ofpair I. and c, d wires of pair II. As it was mentioned above, also these circuits are coiled.

Regarding fact, that capacity CF of phantom circuits of DM quads is to be multipliedby 1,6 CK(by XNCF

.= 3CK to large capacity - it is not suitable for compound circuits)

and resistance R halved, than is valid from there for the same demand of attenuation forboth types condition


LPF = 0, 4LPK

Superphantom circuits have worse transmitting attributes, being used then onlyfor teletype subscriber line. As it is evident from figure, superphantom circuit is realisedby two quads.

Practical performance of coiling pupinizationCoils were manufactured originally from tin, later using torroid magnetic core, sendust

and during last decades are used ferrite cores (H22, H26 - potties with airspace).

4.5 Symmetrical HF cables and cables for digital transmission

There were used telephone carrier transmissions and utilised suitable attributes α, β andZc in higher range of frequencies (up to 10 kHz). Only cross quads insulated by paper- air were used (12 to 252 kHz - 60 channels) and quads insulated by styroflex - air (12to 552 kHz - 120 channels). Profiles 1, 4, 7 and 12 quads with Øφ 0,9 and 1,3 mm. Foreach direction of transmission were used independent cables (directions A - B, B - A). Fortransmission of digital systems of 1st order (PCM) exploiting 32 channels/pair are utilisedcurrent cables. For digital systems of higher orders is utilisable cable 4 x (7 P 0,8) + 2 P0,8. It is composed of wires Cu 0,8 mm insulated by foamed polythene twisted into pairs.Seven pairs (different winding) are coupled into group, which is shielded by Al foil. Cablecore is composed of 4 groups with double shielding and perimeter insulation of z polyesterfoil. Cable is equipped by continuous polythene coat with eventual mechanical protection.Cable is available for bit rates up to 34 Mbit/s, that means enabling of transmission fordigital systems of 3rd order for 480 telephone channels.

4.6 Coaxial cables

There is not possible to use symmetric cables for transmission of broader frequency ranges.(problem of coupling balancing). Therefore are used coaxial cables, where is no influencingof parallel pairs. Conductors of one pair are composed in concentric form. They createcoaxial tube with central conductor (Fig. 4.8).

Arisen electro-magnetic field remains only inside the tube and current passes by highfrequencies only through surface of inner conductor and surface of tube. Shielding impactof outer conductor is insufficient by lower frequencies (n.104Hz). Therefore it is equippedby special shielding for this frequency range composed of two coppered steel bands windedover outer tube. Outer cylindrical conductor is also firmed by this measure. Outer con-ductor seems to be of winded copper tin (about 0,20 mm), which surrounds polytheneinsulating bobbins (distanced one of other 20 - 25 mm) drawn on inner conductor. Mutualinsulation of conductors may be also provided by full foamed layer of polythene (markedα) or by balloon insulation, created of polythene tube, screwed in regular small distancesto inner conductor. This type is used by small coaxial tubes, typically 1,1/4,4 mm. Outertube may be spliced in its seam by serration, milling or it is simply edged. (the newestdesign). Peripheral insulation is winded of paper or polyester band and is numbered in


accordance with position of tube inside cable. Tubes are composed into cable profile nonreflecting direction of transmission and are combined with symmetrical quads, eventu-ally audio (radio) pairs and other pairs. (There is necessary to install some circuits foroperational communication, signalling, remote measurements, etc.).

Figure 4.8: Coaxial pair

Resistance of both conductors is not the same and therefore it is valid:

R = 83, 5√f(

1

d+

1

D) [Ω/km] (4.24)

where d and D are diameters of inner conductor and inner diameter of the tube [mm],f frequency [MHz].

Specific capacity is

C =56εrlnD

d

[nF/km] (4.25)

and εr seems to be 1,15 - 15.Specific inductance is

L = 0, 2lnD

d(4.26)

Leakage is

G = ksωC, (4.27)

where ks may be 0, 5.10−4 = 0, 005%


For calculations of α, β, Zc are valid equal relations as for symmetric cables. Curve ofattenuation is parabolic, given by increasing of effective resistance.

The manufacturing of coaxial cable for telecommunication was stabilised to two com-mon types: so-called medium and small coaxial pairs.

Medium coaxial pair has inner copper conductor of diameter d = 2,6 mm, ballooninsulation (older type bobbin - KMB - 4, first coaxial cable in CZ network with 4 mediumtubes and 5 cross quads 0,9 Cu) and outer conductor from copper band with undulatededge, winded by longitudinally seamed into tube of nominal inside diameter 9,4 mm. Pairsare marked 2,6/9,4. The ratio of inner conductor and outer tube is not random, but itis for copper and dielectrics εr = 1, 2 and µr = 1 and is determined from the relation forattenuation, when it is valid

α =0, 024

D

√f(D

d+ 1)

1

lnDd

(4.28)

There is evident from this relation, that for definite

D

d= x

α will be minimal.Let first derivation be zero

dα

dx= 0

and then we obtain

x =D

d= 3, 6 (4.29)

This is the ratio of tube diameters, minimising specific attenuation.It enables telecommunication transmissions in frequency range 300 kHz up to 60 MHz,

impedance 75 Ω and specific attenuation 3,6 dB/km by f = 1 MHz and temperature 10oC.There is performed possible variant of medium six tube coaxial cable in Fig. 4.9 combinedwith 4 audio pairs of 1,3 mm wire diameter and insulated styroflex - air, 6 cross quadsinsulated by polythene and 4 supervision wires of 0,9 mm diameter. Schematic marking:6x2, 6/9, 4 + 6XN0, 9 + 4RP1, 3

Small coaxial pairIt was developed as a complement to frequency gap, which was evident between ability

of HF symmetric quads and medium coaxial pairs designated for backbone transmissionscrossing extreme distances with large numbers of channels (1920, 2700 up to 3600 andexceptionally 10 800 channels).

It does not differ by its principle of above described medium coaxial pair. Significantdifference is in tube ratio, which is for copper 1,2/4,4 mm. It is equipped by ballooninsulation and has following parameters: impedance 75 Ω by f = 1 MHz, specific attenu-ation 5,22 dB/km by f = 1 MHz and temperature 10oC. It enables transmission up to


Figure 4.9: Composition of coaxial cable core

12 MHz for telephone as well as TV video signal. It was crucial for development of CZtrunk telecommunication network in seventies and eighties of last century.

Composition of cable core varies, most frequently used by us is the type MCBKQY6x1, 2/4, 4 + 5XN0, 7 + 6RP1, 3 + 6X0, 6 + 2P0, 9

Micro coaxial pairThe usage for digital systems of second and third order as well as for data transmissions

is possible. Diameter of inner conductor varies 0,6 up to 0,8 mm, outer tube 2,2 - 2,8mm. The insulation is usually foamed polythene or balloon type. Impedance 65 - 75Ω.

4.7 Special cables

Audio (radio) cables

Radio pair of diameter 1,3 - 1,4 mm is shielded by metal plated paper, eventually byaluminium foil (aluminium foil equipped by layer of thermoplastic mass) and is windedby copper wire 0,3 mm.

These pairs are placed variably into cable cores, as it is mentioned before, eventuallyas special individual cables.

Example: 37 RP 1,3It is designated for audio transmission:50 - 10000 Hz type A,50 - 6400 Hz type B,30 - 15000 Hz type Q.There is also used coiling (3,2 mH with step 1830 m, later for special cables it was

halved to 915 m). Halved coiling step enables upgrade to 17 000 Hz. These special cablesare used for transmissions of modulating signal among radio studios mutually and totransmitters.

Self-contained cables (catenary)Cables with polythene insulation are suitable to be constructed as self-contained and

as it is clear from their adjective, are equipped by carrying cord. They create together


unique unit and are designed to be hanged up mast traces - see Fig . 4.10. (utilising firstof all existing old traces).

Figure 4.10: Self-contained hanged cable

Older type of self-contained cables was hanged on steel cable by suspensions (Fig.4.11)

Figure 4.11: Hanging (catenary) cable

Submarine cablesThe most important requirement for submarine cables consists in operational reli-

ability together with extreme resistance of outer coating against humidity as well asmechanical resistance.

Telecommunication waveguidesTelecommunication waveguides are lumped into group of new perspective lines. They

are manufactured as tubes, most frequently of radial or rectangular cross-section usingqualitative conductive materials. Transmission of electromagnetic energy based on thesame principle as in atmosphere, but on strictly defined direction and frequency. Limitingof frequency depends on critical wavelength λ = c/f being dependent on their construc-tion. Radial metallic waveguide is demonstrated in Fig. 4.12. Steel tube is metal-platedand then lacquered. Protective coating covers its surface.


Figure 4.12: Metallic radial waveguide

Spiral waveguide is demonstrated in Fig.4.13. This waveguide is created from copperconvolution coated by dielectrics, followed by shielding and coating in upper layers. Alsois known the body created by convolution in metallic tube, etc. Advantage of spiralwaveguide is in fact, that it filters parasite waves generated in non-homogeneous pointsof wave link.

Figure 4.13: Spiral waveguide

Results of experimental operation have proven availability of realisation traces oflength about 10 up to 30 km, attenuated 2 dB/km - designated for 100000 up to 200000telephone channels.

Telecommunication superconductorsThey are based in accordance with knowledge, that by temperatures convergent to ab-

solute zero (−273oC) value of resistance is decreasing up to one quarter of that by classicalconductors. There is possible to transmit signal alongside extreme distances without am-plifiers. They are constructed as analogical as coaxial cables (one or more tubes; materialtantalum, lead), covered by outer layer of nitrogen or helium for keeping low tempera-tures of conductors. However they require being equipped by special refrigerators placedalongside trace every 10 to 20 km, these are extremely expensive.


4.8 Structured cabling systems

Structured cabling systems enable easy installation in buildings for networks as LANfor data and voice networking. The special construction of twisted pair was developedtogether with very precious manufacturing as a response to the demand for permanentupgrade of bit rates. Manufacturing of these innovated copper pairs is advanced man-ufacturing process guaranteeing equal distance of conductors, tracking forces are super-vised during production, special care is focused on twisting and insulating of conductors.Thanks to these manufacturing processes are guaranteed minimised capacitive unbalances,minimal differences of conductor attenuation, minimal values of near- as well as far endcrosstalks. (NEXT and FEXT). There are also minimised differences of impedance andreturn loss.

As to availability to operable frequencies these systems are sorted into following cato-gories:

• 1,2 for voice services operation

• 3 for data, l0 Mbit/s (ISDN)

• 4 for data, l6 Mbit/s (Token Ring Ethernet)

• 5 for data,100 -300 Mbit/s (ATM, Ethernet)

Example: Cable BELDEN 1584A number of pairs: Zc ∼ 100Ω, Ø0,51mm, C=49,2pF/km

f max α[MHz] [dB/100m]

4 3,6710 5,7716 7,3831 10,39100 19,52

Specification of cablesRequirements for four pair cables specified of impedance 100 Ω used in networks are

specified in several standards altogether. Wiring of outlets by physical link, usage ofunique pairs, colour coding of pairs, transmitting characteristics, tested parameters, test-ing methods and principles of cabling construction for four-pair of category 3, 4 and 5unshielded twisted pair (UTP) a next technical equipment needed for cabling is describedin standard EIA/TIA-568. Cabling by twisted pair covers complete series of cable typeswith nominal impedance 100 Ω . Beside above mentioned four-pair twisted pair cableare also more capacitive cables containing 25 or more pairs of shielded or unshieldedconstruction. Both basic constructions are disposable in all categories. Unshielded cableof category 3 is standard telephone cable. Connectors used in networks are of the sametype, those we can meet by modern telephone systems. There is connector RJ-45 with 8outlets or Telco connectors with 50 outlets. For administration of standard interconnect-ing panels (patch panels); addition of new access points, changes in coupling of access


points, cancellation of not needed access points is able to provide as easy as by ordinarystructured telephone or data cabling. Closer specifications for cables of categories 4 and5 may support operation for longer distances - cables of category 5 support distances upto 150 m e.g. Cabling passing through interconnecting boards to terminating nodes maybe terminated in mural sockets equipped by connectors RJ-45 as well as be terminatedby these connectors directly.

Example of connector RJ-45 wiring is in Fig. 4.14

Figure 4.14: Outlet assignment of cabling 5-UTP

Testing of UTP cables, parameters and their acceptable range for operation of100VG- AnyLAN network. There are same parameters, these are required by lOBase-Tnetworks including that in case of 100VG-AnyLAN networks is required more option fortesting all four pairs for tested frequencies up to 15 MHz.

Testing frequency is used for cable verifying for network. Attenuation describes loss ofsignal due to the signal passing through conductor. The attenuation is as large as lengthof cable. In case of too high attenuation, receiver will not be able to decode received data.

Characteristic crosstalk among pairs (pair-to-pair crosstalk) is inflicting of signal inone pair by other neighbouring pairs.

Multiple Disturber Near-End Crosstalk - MDNEXT predicates of influencing size ofsignal in one pair inflicted by signals of all resting pairs of cable - measured at end ofcable using disturbing source of signal by four paired cables.


Cables with shielded twisted pairStandards for twopaired STP (Shielded Twisted-Pair) cable of impedance 150 Ω offer

in case of their use solid base. Standards ElA/TlA 568, TSB 36 and 40 as well as newlysuggested standard 568 and presented by SB 2840 specify wiring of connector outlets,colour coding, characteristics of signal propagation, strategy of cabling describes attachedtechnical equipment too.

Section of cabling systemEach structured cabling is sectioned into following parts:

• section CAMPUS performs interconnection of buildings

• section RISER creates backbone distribution

• horizontal section is created by fixed distributions frame for individual offices

• operational section interconnects horizontal section into terminating equipment

Situation is imaged in Fig. 4.15.

Figure 4.15: Scheme of cabling system

CAMPUS section is realised mainly by optical cable due to larger distances betweenfacilities and also their galvanic separation. Next argument for optical cable is also passingof link related to data stream.

RISER section (backbone line in building) uses also optical cable in role of trans-mitting media. Main reason is passage of link, in some cases also galvanic separation ofindividual sections of network. The backbone is realised also by metallic cables. Thereare used multi pair cables (25 pairs e.g.) for categories 3 and 4.


Horizontal section is almost exceptionless created by star distribution of 4-pairedmetallic cables. Centre of the star is performed by point of interconnection to backbonedistribution frame. Optical cables are seldom used in horizontal section.

Work section contains connecting cables. There are metallic 4-paired cables usingconnectors RJ45 (so called Patch Cord ) or optical interconnecting cables. Type of con-nector by these cables is given by used active equipment (mainly ST or SC connectors).Operational section serves to interconnecting of horizontal section link into terminatingequipment. There is interconnected socket with computer in the one side of link e.g., inthe opposite side is interconnected link in data distribution frame from Patch Panel intoactive element.

Example of system design (see Fig.4.16):

Figure 4.16: Scheme of cabling system: CR - campus cabinet, RR - backbone cabinet,HR -horizontal cabinet, Z - sockets

These systems are advantageous seen by quality and bit rates, easy installation andmaintenance, reduction of mistakes by installation and interconnecting.

4.9 xDSL Transmitting

There were mentioned several times before about quality and great possibilities and ad-vantages of optical fibres. (They will be focused individually in chapter 6). Their succesfulintroduction in transport (long haul) networks is doubtless. Such a complete introductioninto access (local) networks is not so definite. There are known systems, they enable thesetransmissions, but up today costs of all experiments are very expensive. Already in pre-vious subchapter was mentioned chance as supported by special technology of ”twistedpairs” is possible to upgrade quality of transmission. There were tried to exploit ex-isting telephone lines, these are wide-spread worldwide. There is told in equity about”dug-in gold” in underground. As first success has been introduction of ISDN (IntegratedServices Digital Network), so-called integrated digital services, enabling transmission of


telephone calls, data (Internet) and fax services. There is also possible transmission ofbrand band services (TV, video), known as B - ISDN (Broadband - ISDN). Other de-velopments offer next more advantageous solutions based on new advanced modulationprinciples (CAP/QAM, DMT there are enabling permanent access, new broad band ser-vices, parallel operation of POTS/ISDN and data, using common subscriber local loop.These systems are named generic xDSL (ADSL, SDSL, VDSL etc.) The roadmap tohigher bit rates demonstrates Fig. 4.17.

Figure 4.17: Trends of bit rate upgrade

The most extensive transmission uses ISDN technology (first of all in Europe), andjust now ADSL (originally in U.S.A., since 1998). Actually it is exploding also in CZ,This technology seems to be the most perspective actually and in accordance with type oflocal loop enables coverage up to 6 km. Parallel operation of date as well as POTS/ISDNservices is posssible. The highest bit rate up to 8Mbit/s (downstream) for local loop length3 km by copper Ø0,6 mm and 640 kbit/s for back haul channel (upstream). Access toservices without dialling (always on). There is ideal means of access to Internet and otherbroad band services. Technology VDSL, enabling much higher bit rates up to 52 Mbit/s(downstream) and up to 6,4 kbit/s (upstream), however enable transmission to only 300m, Ø0, 6mm copper. These transmissions are suitable for business users, universities,etc. (Compare with optical transmission). More detailed information about modulationprinciples and techniques offers item Theory of communication, about network elements,modems, etc., and item ”Architecture of networks”.

4.10 Examples

A) Demonstrate relation between value of inserted coils for single pair and compoundcircuit (phantom).

B) Determine conditions for reflection of open and short cut line.


5 Shortcomings of telecommunication cables and In-

homogeneities

5.1 Non-homogeneities of cables

There is not real to manufacture telecommunication cables absolutely perfect. (maybetheoretically yes, but seen by economic view such a manufacturing would be unrealisable).Therefore it is necessary to search for compromise between perfection and costs.

The reasons of shortcomings are as follows:

• By copper wire production. There is not possible to produce wire of preciselynominal diameter. (Wires are tracked through calibres. These calibres are step bystep stolen and diameter of wire is slightly enlarged),

• Analogically it is not possible to produce insulations of absolutely precise qualityand thickness,

• There is not possible to reach precisely identical windings and pressures by twistingpairs, quads and all cable cores to reach identical electric attributes for all cablelengths.

There is necessary to permit certain tolerance of cable electrical attributes as it waspresented before. These shortcomings are sorted into two types:

1) non-homogeneity of primary parameters R, L, C, G and

2) asymmetries of particular capacities, leakages, resistances and inductive couplings(only for symmetric cables).

5.2 Non-homogeneities of cables

Due to the imperfection of manufacturing (wires, insulators, etc.) quads of individualproduced lengths slightly differ in values of effective resistances R 1, inductivities L 1,operational capacity C l leakages G 1 (critical by long haul quad cables are first of allC 1). Differences of primary parameters of individual cable lengths by splicing in cablejoints inflict arise of slight reflections, particular reflections of electromagnetic waves, thereare transmitted to beginning of line and further as multiple reflection also to the end ofline. Particular voltages in the beginning of line are proportional to particular reflectedwaves. Their geometrical sum gives voltage U1r (reflected) and particular currents, theirgeometrical sum gives current I1r.This resulting reflected voltage U1r is geometricallyadded with original voltage U1, which is finally changed into U ‘1.

U ‘1 = U1 + U1r


Change of input impedance is equal to changes of U ‘1 and I‘1 in the beginning of line(instead of original Z1 = Zc)

Z‘=U ‘1I‘1

Frequency characteristics, input impedance of line (without reflections) Z1 = Zc =ϕ(f) is flat, frequency characteristics, input impedance of line and by particular reflectionsZ‘ = ϕ(f) is irregularly undulated. Undulation of impedance characteristics aggravatespossibility of line imitation by balancer (used by termination of line), therefore is decreasedunbalance loss anv, Aggravation of imitation at receiving site, by another words decrease ofloss unaccommodation anp and leads to aggravation of stability, echoes or so-called indirectfar end crosstalks FEXT. These shortcomings inflict by TV transmissions defocusing ofpicture and in case of more significant reflection suitably delayed, it will be exhibitedby other equidistant weak picture. There is important for frequency characteristics ofinput (output) impedances of line should be as far as flat. We reach it by precisionby manufacturing and further first of all quality by assembling of cable, as it will bementioned as follows.

Measures for minimising of non homogeneities of line:

- By manufacturing: There is necessary to be focused on input supervision of suppliedmaterials and provide supervising operations by manufacturing consistently.

- After completion of all manufactured cable lengths for one section and after finishingall final measurements will be done so-called allocation of cable lengths, it meansplan of placement of individual cable lengths alongside trace.

The goal of allocation is to place cable lengths with minimal deviation of wave impedanceby certain f=const. and to place best lengths to margins of whole section. By anotherwords lengths with minimal deviation of nominal value. As an example we performmethod of allocation for coaxial cables. Manufactured lengths for one amplifying sectionare to be divided into five groups from the point of view of characteristic impedance Zc[Ω]of ever manufacturing length: group I 74,35 - 74,65 (mean value 74,50), group II 74,66 -74,90 (mean value 74,78), group III 74,91 - 75,15 (mean value 75,03), group IV 75.16 -75,40 (mean value 75,28), group V 75.41 - 75,65 (mean value 75,53).

Laying of individual lengths is done by such a way, that to both ends of amplifying(repeating) section will be placed the best lengths of III. Further composition is doneto neighbouring lengths should be of neighbouring impedance group. So differences ofimpedance in joints will be minimised.

There is not measured impedance Zc[Ω] of symmetric cables, but operational capacityC. is not which influences Zc. Allocation is derived of mean value of operational capacitydeviation. (composition of lengths alongside traces).

Assembling: Operational capacity is compensated by jointing minimal deviations ofneighbouring quads. Quads are selected as to positive (+∆C) or negative (−∆C) devia-tion so by two lengths will be


C‘ + ∆C + C‘−∆C = 2C‘

These asymmetries could be found only by symmetric cables i.e. by cables paired orwith quads (they need not be mechanically symmetric). In contrary is coaxial pair, whichis to perfection mechanically symmetric and hereat is electrically asymmetric.

5.3 Asymmetry of capacities and leakages

Asymmetries of partial capacities and leakages, so-called lateral asymmetry could beexplained using schematic imaging of quad (Fig. 5.1), which is composed of pair 1 (con-ductors a, b) and pair 2 (conducotrs c, d), with appropriate partial capacities and earthcapacities C‘ad, C‘ac.C‘bc, C‘bd, C‘ab, C‘cd and earth capacities C‘ao, C‘bo, C‘co, C‘do.

Figure 5.1: Scheme of partial capacities inside cable quad

Partial capacity is capacity between two conductive objects (conductors, metal plates,armatures, conductor and earth, etc.), which is done by geometrical configuration ofconductive object (as form, lay, distance) and dielectrics between them. There is possibleto measure partial capacities; they do not enforce themselves independently. We willtransform quadric armed star of earth capacities C‘a0, C‘b0, C‘c0 and C‘d0 into equivalentcomplete polygon, which is imaged in Fig. 5.2. These capacities are signed by two dashesin this figure and they are added parallel to partial capacities among conductors. Effectivepartial capacities are so created, i.e. effective partial capacities between two conductorsCab, Ccd, Cac, Cad, Cbc, Cbd performed in Fig. 5.3. Regarding fact, that we consider in nextthoughts by crosstalk circumstances of individual quad, we may eliminate C’ab, C’cd,while crosstalks are not influenced by these effective partial capacities inside first andsecond pair.

This performed simplifying is imaged in Fig. 5.4 of it is evident, that this couplingperforms the partial capacities arranged as Wheatstone bridge. In case of precious identityof all these capacities C‘ac, C‘ad, C‘bc, C‘bd the bridge is balanced and current of source


Figure 5.2: Partial capacities transformed from star of four earth capacities to fullpolygon

Figure 5.3: Network of effective partial capacities inside cable quad

diagonal (pair 1) will not penetrate into diagonal of indicator (pair 2).; no capacitiveasymmetry as well as crosstalk arise.

In case of unbalanced bridge (effective partial capacities differ mutually, compositionis not symmetric), capacitive asymmetry arises between 1st and 2nd pair. This capacitiveasymmetry is marked as k1 and in Fig. 5.4 is drawn as dashed. Part of current penetratesfrom 1st to 2nd pair effecting as crosstalk.

Asymmetry of effective partial capacities of one quad (ranged as electrically shortelement) caused therefore crosstalk between circuits of this quad. Unbalanced bridge ofpartial capacities causes crosstalk. Crosstalk minimising is provided by such a measure,that bridge could be balanced by additional capacity k1. (as to the result of measurement)as it is evident of Fig. 5.4 e.g. Additional capacity is named as capacitive asymmetry andbalances bridge of effective partial capacities.


Figure 5.4: Capacitive bridge of effective partial capacities of quad

We use often coupling in accordance to Fig. 5.5 for simplifying of calculation ofcrosstalk.

Figure 5.5: Fictional capacitive coupling k‘1

(Compensation for Fig. 5.5 without capacitor k1) in which two conductors are coupledby capacitor k‘1 which is called fictive capacitive coupling and resting two conductors areconnected directly. Value k‘1 is dimensioned so to current Is will flow through telephonereceiver as in case of Fig. 5.4. As it will be further evident, there exists simple relationbetween k‘1 and k1,: (k‘1 = k1/4). Equivalent coupling is in Fig. 5.5b, which is used bysolution of theoretical thoughts of crosstalk.

As to asymmetry of partial leakages, which are inflicted by loss in dielectric, thereis no critical situation as in cases of partial capacities asymmetry. Partial leakages areimaged as parallel coupling of gac, gad, gbc gbd to partial capacities We gain then complexadmittance (Fig. 5.4.). gac + jωCac etc.

Let us explain term of functional capacity concluding this chapter. Let us markeffective partial capacities Cac, Cad, Cbc, Cbd as x and capacity Cab as y. Then resultingoperational capacity of length l will be simplifying this task:


Cl = y + Σx

This situation is imaged in Fig. 5.6. Two capacities x are always in series (x2) and these

capacities are parallel to y. Operational capacity is effective partial capacity between twowires, creating one circuit (pair, phantom) by 1 = 1 km sometimes. There is not possibleto speak about ”asymmetry C” as it is sometimes incorrectly used; therefore it is onecapacity connected between two conductors (circuit) and cannot asymmetry itself.

5.4 Magnetic asymmetries

There are so-called longitudinal asymmetries, there have as real components (resistanceasymmetries), as imaginary real components (asymmetries of inductive couplings). Induc-tive couplings arise in electrically short sections among individual wires of quad. (Partialmutual inductivities), these are imaginable as transformer couplings mac,mad,mbc,mbd -see Fig.5.7.

Figure 5.6: Capacitive asymmetry k1 and functional capacity C.l of manufactured length

We obtain also unbalanced bridge by differing inductive couplings with crosstalk asresulting effect. Regarding fact, that we are interested again in asymmetries between 1stand 2nd pair, we may provide compensation in our theoretical thoughts of crosstalk andconsider only fictive inductive coupling between pairs, signed m‘1 (see Fig. 5.7b). Allegedcouplings among individual conductors have also real components, inflicted by lossesof whirling currents inside conductors and in coating, these may inflict by asymmetricconfiguration crosstalk.

So-called resistive asymmetries of individual pairs Ra −Rb and Rc −Rd cause unbal-ancing differential bridges of pairs 1, 2 - (As it is imaged in Fig.-5.8) and then arise ofcrosstalk between 1st and 2nd pair or phantom respectively. Analogically inductivities ofindividual conductors La−Lb and Lc−Ld (see Fig. 5.7) may inflict crosstalk between 1st

and 2nd pair.We are able to enunciate, that cause of crosstalk by symmetric quaded cables are

asymmetries of partial capacities, leakages, inductivities and resistive couplings.


Figure 5.7: a) Partial inductive couplings among wires of unique quad, b) fictionalinductive coupling

5.5 Corrective measures of asymmetry

Corresponding measures are provided as by manufacturing as by assembling.Measures by cable manufacturingI. Technological measures:As it was mentioned before, the best measure for minimising of asymmetries is precious

manufacturing. There is possible to reach identical resistance of all four conductors in onequad by using of wires from the same coil of wire. Identical diameter of wire is reachedby this measure. Analogically it is necessary to process by preparation of insulatingmaterials. There are supervised intermittently k1 − k3 of quad itself.

II. Construction of cablesCapacitive asymmetries are more significant in compare with magnetic ones by low

frequencies (up to 15 kHz). DM (Dieselhorst - Martin) quad presents better results asto capacitive asymmetries in compare with cross quad. Despite DM quad has higherfunctional capacity C in contrary to cross quad (38,5 nF/km vs. 34,0 nF/km) to reach onthe other hand lower C for phantom circuit and there is secured mutual perfect changingof all four wires in quad; therefore is reached practically identical mean value of distancefor individual wires among themselves and then approximately identical partial capacitiesamong conductors.


Figure 5.8: Resistive and inductive asymmetries of 1st and 2nd pairs

Magnetic asymmetries are more important in range of higher frequencies (carrier sys-tems) in compare with capacitive ones and therefore cross quad is better for this purpose.There depends on inductive couplings among individual wires (i.e. on face of loops, cre-ated by two neighbouring wires). Equity of these loop faces is reachable much easier bycross quad in compare with DM quad.

Measures by assembling: Assembling of cables composes of following steps: I.Symmetrizing This is process, by which are decreased capacitive asymmetries jointingelectrically short sections of cable. Symmetrizing is done:

1. Choose of quads and crossing,

2. Additional capacitors.

Symmetrizing is called in cable-fitter argot of English douping. This process is possibleby acoustic frequencies; several manufacturing lengths may be symmetrized up to sectionof 2 km. There is not possible to symmetrize using higher frequencies, while manufacturinglengths are (seen by only several quads inside the cable) longer in compare with LF cables,460 m e.g. (in contrary to 230 m by LF cables) and there are not electrically short.

II. Direct minimising of crosstalkBy completing longer section as to be described as electrically short as well as individ-

ual length itself the symmetrizing is not available any more and next step is coming i.e.direct balancing of crosstalk. This operation is not oriented to causes of crosstalk itself,but to resulting effect of asymmetries, crosstalk directly. This method changes directlycrosstalk or effective admittance couplings in defined point of line. In case of FEXT at


the end, NEXT should be compensated in direct point of bad coupling. Crosstalk is de-creased by crossing of pairs and quads in suitably placed joints. This process of crosstalkminimising by jointing longer sections of cable is called poling.

III. Final balancing - fine symmetrizingAbove mentioned measures are not usually sufficient to reach demanded crosstalk

attenuation, particularly cables exploited by carrier system. Thus in finish next, third stepof assembling. That is fine balancing due to compensating (balancing) by compensationwiring. - most frequently at the end of amplifying section. As it is evident, measures andmethods for homogeneity upgrade or by another words minimising of crosstalk are verycomplicated.

5.6 Non-homogeneities of lines

Previous chapter was focused onto shortcomings of telecommunication cables, first of allseen by on manufacturing length. (l = 230 m). Let us broaden up this moment studiedproblematic for case of connecting individual lengths as well as for tapping of terminatingequipment. There is evident, that for keeping homogeneity (amplifying section e.g.) cor-rect adapting of equipment impedance and characteristic impedance of line in broad fre-quency range. There is practically unrealisable to reach ideal status. Despite this fact wetry to accommodate real situation through minimising of impedance non-homogeneities.Shortcomings inflict such phenomenon, that part of voltage and current waves reflectedform impedance non-homogeneities alongside line including non-adaptation of equipmentand line impedance is reflected after return to the beginning of line again back to far end.There is other reflection inflicted again. We will investigate reflections more detailed aswell as measures for securing homogeneity.

Theory of arise single and multiple reflections by homogeneous line and their impacts.

Characteristic impedance Zc of homogeneous line by defined frequency is not constantalongside whole distance, but differs off mean value Zc due to partial non-homogeneitiesby deviation Z(x). Deviations Z(x) in manufacturing lengths are inflicted by primaryparameters of line, caused by deviations of wire diameters, mutual wire distance, non-homogeneity of wires, deformations of elements by manufacturing and cable laying. Nextdeviations Z(x) may arise by splicing of individual manufactured lengths, by those varymutually followed values Zc. Every impedance non-homogeneity causes reflection of waveparts of voltage and current propagating alongside line. If reflected wave returnins tobeginning of line meets impedance non-homogeneity point, part of wave is again reflectedback, i.e. in direction of primary progress of main wave to the end of line. Principle ofreflections demonstrated in Fig.5.9 is repeated on all impedance non-homogeneities. Sumof all once reflected voltage and current waves causes change of input impedance of lineand therefore change of useful signal load too, which is transmitted into the line. Changeof input impedance is frequency dependent, thus undulation of frequency characteristicsas well as resting attenuation. Sum of all twice reflected voltage and current waves willinflict troubles in the far end of line. Impacts of thrice and more multiplied reflections ispossible to neglect, while these reflected voltage and current waves are severely attenuated.


From before mentioned facts it is clear, that every impedance non-homogeneity disturbstransmitted signal and causes decrease of signal/nose ratio. As we have mentioned meanvalue of Zc and deviations Z(x), there may be for defined frequency image as in Fig. 5.10.

Figure 5.9: Scheme of reflected waves of voltage and current of impedance non-homogeneities

Figure 5.10: Undulated characteristic impedance around its mean value

Characteristic impedance Zc distant x from the beginning of line is

Zc = Zc + Z(x) (5.1)

Function Z(x) we will call as function of undulation, thus characterises undulation ofZc around its mean value.


Let is in point x in length element of line dx jump of impedance Z1(x)−Z2(x+dx) =∆Z(x), then reflection factor in this point is

p =∆Z(x)

Z1(x) + Z2(x+ dx)(5.2)

Though impedance deviation Z(x) is in contrary to mean value of impedance Zc toosmall, we are able to define reflection factor as well as difference of impedances Z1(x) −Z2(x+ dx) = ∆Z(x), reflection factor could be as follows

p.=

∆Z(x)

2Zc

(5.3)

Then for reflected voltage from non-homogeneity in the point x of line, which seemsto be in the line beginning as disturbing voltage U1bl may be written:

U1bl = U10∆Z(x)

2Ze−2γx (5.4)

where, γ = α+ jβ is specific propagation constant.Introducing disturbing voltage factor by reflection in near end Pn(ω) (ratio of disturb-

ing reflected voltage U1bl in the beginning of line and effective voltage U10 in the beginningof line), the relation (5-4) may be overwritten for single point of reflection

Pn(ω) =U1bl

U10

=∆Z(x)

2Zc

e−2γx (5.5)

In case of equally distributed non-homogeneities alongside line the resulting disturbingvoltage factor by reflection in near end of complete line

Pn(ω) =1

2Zc

∫ l

0e−2γxdZ(x) =

1

2Zc

∫ l

0(Z(x))‘e−2γxdx (5.6)

where (Z(x))‘ is derivation of undulation function Z(x) as per x.There is evident, that decrease of disturbing voltage values may be reached only due

to decreasing of non-homogeneities alongside cable line.

5.7 Examples

A) Cable 1,3mm Cu has Ck = 38, 5µF/km. Appoint functional capacity for maniufac-turing length of 230m?


6 Wireless transmissions

6.1 Radio transmissions

We apprehend this concept as telecommunication supported by radio waves. For the fixedterrestrial service utilising radio links and fixed satellite service are most important fortelecommunication purposes. Both types of systems are operated in microwave ranges andare exploited for transmission of telephone calls, data, TV and audio signals. Anotherapplication of radio communication transmission are as follows radio broadcasting inbands of ultra short, short, medium and long waves, terrestrial TV broadcasting andsatellite broadcasting. Long haul transmissions were launched by cable links, it seemedto be sometimes, that radio transmission overruled cable ones during previous decades(shortwave and satellite broadcasting); optical transmissions turned situation back again.Actually mobile radio communication is gaining supremacy. There is possible to state,that cable and radio (wireless) transmissions are now complementing themselves mutually.Radio links may be used as hot reserve in case of cable fault and vice versa. Radiolinks are used first of all in mountains due to their quick installation and by buildingof mobile operators networks. There were extraordinary important during launching ofdigital overlay network in CZ. Blocked scheme of radio link system performs Fig. 6.1

Figure 6.1: Scheme of radio link system

Between source of signal (ZS) and modulator (M) is possessed block for signal pro-cessing in basic band (ZZS). It depends on transmission type - analogue vs. digital. Nextfollows transmitter block (V) and aerial system. Bands from 1 up to 10 GHz are exploitedin radio links and fixed satellite service. Parabolic aerial systems are utilised for trans-mitting emanation as well as for receiving. This system is composed of primary emitterand rotary parabolic reflector. Spherical wave strikes on surface of parabolic reflector tobe reflected. This wave is transformed from spherical to plain wave, which is emanatedby mouth of parabolic reflector. Receiving site is composed analogically by receiver (P),detector (D) and circuits of signal processing (ZZS). Radio link points are built up onsuitable heights distant 30 - 70 km securing direct visibility as links of point to point type,eventually for longer sections are inserted so-called ”radio relay” (composing of receiverand transmitter with change of carrier frequency). These type systems are exploited fordata transmissions, for connecting distant localities to networks LAN, etc. Naturallywhole problematic is much more complex; radio waves propagation is to be studied seenby noise, bandwidth and other parameters.

6.2 Satellite transmissions

The most important for telecommunication are satellites stationed up geostationary tra-jectory linked with fixed terrestrial stations. Satellites are stationed in height of 38 600 km


and observed from the earth surface seem so to be as stationary. Intelsat is an example.There are exploited for telephone calls, data transmissions, TV, ets. Intersputnik systemof former Soviet origin covers Nordic, Indian and Atlantic areas utilising composition ofthree satellites following extreme eclipse trajectory around earth poles.

6.3 Mobile transmissions

These systems have been explosively developed in recent years. There are permanentlyupgraded as seen by offered services as comfort of subscriber terminals. (video and TVtransmissions). The principle lies in cell structure, where transceiver dispatches demandsof subscribers. Transceiver is linked by radio link, optical fibre or cable into higher networklayer up to control switch. The switch interconnects subscribers of the same operator (O2,T-Mobile, Vodafone in CZ) or provides mutual interconnection into network of otheroperator or into fixed line (O2), or abroad (More detailed in the items Radio and mobilecommunication - Subscriber terminals).

6.4 Optical transmissions

Cable-less optical transmissions utilise laser link and atmosphere as transmission medium.There are links with direct visibility easy realisable and are not determined by officialpermission for operation as in case of radio links. There are duplex links exploiting opticalcarrier frequency, load of which is concentrated into narrow beam. Mostly digital intensitymodulation is used. There is reached reliability closing up to 0,999 using new principles.(multi channel transmission - higher costs). These systems are produced by prestigiousmanufacturers. Transmissions of bit rate 155 Mbit/s bridging distance up to severalkm are more frequently used. Application may be found in networks LAN and MAN.Second method of optical cable-less transmission is to be realised by emitters IR-LED tocover room space for wireless connection of PC, headphones, interpreter equipment etc.Emanation is radiated diffusively and by reflection.

7 Optical fibres and cables

7.1 Basic principles of transmission

Transmission of information through optical fibre is enabled by light ray. Specialities ofinformation transmission are derived from differences between electrical and optical lightsignal. Signal carriers are crucially different. These carriers are live electrons by galvaniccoupling as by optical coupling neutral photons, there are not influencing themselves mu-tually. No magnetic and electric fields are arose, these are reason of various parasitecouplings. Optical link is immune against outer disturbing signal and hardly to side hear.There is no back influencing from output to input. Linkage is absolutely unidirectional.Full galvanic separation of input and output seems to be also advantageous. Optical linkis in basic form composed by modulated ray source, optical environment and by receiver


of emanation. Input and output signals of optical link are electric, and so transmitting aswell as receiving instalments contain except optoelectronic elements and optical systemsalso electronic circuits for input and output signal processing. Basic composition of onepossible variant of optical link is in Fig. 7.1. Light source seems to be laser or luminiscentdiode. Light ray is modulated in optical modulator or in case of semiconductor sourcedirectly by changing of energising current. The task of transmitting and receiving in-stalments of optical system is to transmit optical signal as possible as low losses fromtransmitter to optical environment and next in receiving site to photodetector. The re-ceiver then transforms light signal back to electric one, by what receiver should secureoptimal processing seen by signal - noise ratio. Circuits of signal processing transform sig-nal into suitable form for transmission, circuits for multiplexing as well as demultiplexingat receiving site, etc.

Figure 7.1: Basic scheme of optical link

Range of optical radiation is placed between 100 nm up to 1 mm and is divided into7 sub-ranges:

- three ultraviolet (100 nm - 280 nm; 280 nm - 315 nm; 315 nm - 380 nm),

- followed by visible light range (380 nm - 780 nm),

- three infrared (780nm - 1,4 µm, 1,4 µm-3µm, 3µm-1mm).

As a limit for optical communication exploitability the range around l0 µm may be con-sidered. Powerful lasers and detectors are available for this infrared range. Significantlynarrower range 0,4 a 1,7 µm in-between is dominantly important for optical transmission ofinformation. Minimal attenuation of materials used for manufacturing of lightwaveguides


corresponds with this range, whereas in the range of ultraviolet rays their attenuationrises. And there are available no effective photodetectors for range close to X-rays aswell as the ray exciting of such high light quantum energy. On the other hand there iscrucial to upgrade little immunity of receivers against disturbing signals in infrared range.Receivers should by protected against disturbing signals radiated by warmed up subjects.Parameters of optical signal are changed by passing through optical environment. This isaccompanied by attenuation as well as to change of transmitted pulses form, eventuallytheir time position. Extension of range is possible by implementation of repeaters, theremay be as amplifying or regenerating. Repeaters of first type amplify across optical bandby laser amplifiers. Addition of noise by every amplifier and consequent degrading of linkquality with increased length of line is disadvantageous. Regenerative repeaters providecomplete renewal of signal to original quality enable based on PCM to create links, qualityof them is independent to length of trace. The invisible light ray is carrier of informationtransmission. Changes of its amplitude, frequency, phase, polarisation as well as durationmay display transmitted information as each of them independently or in suitable com-bination. There is necessary to consider random character of photon radiation by opticaltransmission as well as by its design. Their impact is noise generation, which is directlypart of optical signal. Principle of fibre optics transmission is based on total reflection onthe dividing line of two optical environments with differing step index of refraction. Theyare created by cylindrical dielectric core with refraction index n1 which is surrounded bydielectric cladding with refraction index n2(Fig.7.2). There is valid n1 > n2, that rays en-tering core under lower angle under smaller angle then Θ, where cos Θ = n2/n1, becomesat dividing line core - coating to total reflection.

Figure 7.2: Transmission by optical waveguide

Lasers (LD) and luminescent diodes (LED) serve as light sources in optical links.LED are non-coherent sources and may be used only for links with lower requirements tobandwidth and range. The most suitable and advantageous source for telecommunicationpurposes of all light sources are semi-conducting lasers. Most advantageous photodetec-tors for links with fibre lightwaveguides are semiconductor photodiode (PIN) or avalanchephotodiode (AFD). Level of useful signal and magnitude in output of photodetector ofnoise are basic parameters defining choose of photodetector itself.


7.2 Types of optical fibres

As to the technology and type of transmission lightguides may be divided into single-mode,-and multi-mode with constant index of refraction of core and coating, or step-index, andgradient (multi-mode) with varying index of refraction.

Single-mode lightguidesThese lightguides have extremely small diameter of core and by defined number-

aperture and wavelength of light enable transmission of only unique, i.e. basic modeof electromagnetic wave. (V < 2, 405;HE11). These lightguides reach lower values of at-tenuation, but extremely small diameter of core makes difficult to couple light into fibre.(Fig. 7.3). These lightguides have lower dispersion, i.e. they have larger transmissionbandwidth. Their excitation is secured by light source with low spectral line (lasers).There are actually most used fibres in long haul transmitting applications.

Figure 7.3: Single-mode lightguide

Multi-mode lightguidesEnlarging core diameter (There is valid following condition V > 2,405), number of

modes, there are able to propagate through fibre is increasing.. Used lightguides of corediameters 50 to 100 µm are propagating by wavelength 0,85 ?m thousands of modes.(see Fig. 7.4.). Arising mode dispersion limits bandwidth to the value of 50 MHz/km.Exploiting is for short hauled usage.

Figure 7.4: Multi-mode step indexed optical waveguide


Gradient (multi-mode) lightguidesThese types of lightguides, exploiting change of refraction index n = n(x) inside cross-

section in transverse direction, mostly with quadratic parabola curve, as to relation:

n = n0(1− α2x2),

enable significant reduction of mode dispersion (see Fig.7.5)

Figure 7.5: Gradient multi-mode optical waveguide

Maximal value of refraction index is in axis of fibre and in direction out of axis islowered in accordance to above described law. There is transmitted halved number ofmodes by the same diameter of core and same difference ∆n of refraction indexes. Thisis very suitable for quality of transmitted signal, when these lightguides reach bandwidthover 1 GHz . km, diameter of core varies approximately 50 to 100 µm with NA roughly 0,2.They are exploited for transmissions up to medium ranges, advantageously for multiplexedtransmissions.

Examples of characteristic parameters of optical fibres Lucent Technologies:

Single-mode fibre with accommodated refraction index profile (MatchedClad, MC)

General characteristicSingle-mode optical fibre with accommodated refraction index profile is composed

of germanium doped core and coated by pure silicon glass. Scheme of refraction indexprofile is imaged in Fig.7.6. Fibre is designated for all applications, where low attenuationand broad bandwidth for higher bit rates are required. Fibre is operable by both usedwavelengths, i.e. 1310 and 1550 nm. The other advantages are as follows:

• extremely low attenuation for both wave lengths,

• excellent geometrical parameters enable to reach extremely low inserted attenuationsof welded splices as sell as connectors,

• doubled primary coating D-LUX 100R secures excellent mechanical and climaticimmunity D-LUX,

• as the fibre is placed into cable Lucent Technologies, the manufacturer guaranteesexcellent parameters of fibre as well as cable seen by polarisation dispersion. Guar-antee of this parameter is important especially for analogue applications (cableTV).


Figure 7.6: Refraction index of SM fibre

Geometrical parametersFibreDiameter of core: 8,3 µm (nominal value)Diameter of coating: 125 ± 1 µmExcentricity of core: < 1%Excentricity core-coating: ≤ 0, 8µm

Primary protectionDiameter of primary protection: 245 ± 10 µmExcentricity. primary protection - coating: < 12µm

Transmitting parameters:Diameter of mode field (MFD): 9,3 ±0,5 µm (1310 nm)

10,5 ± 1,0 µm (1550 nm)Limiting wavelength (λcut off ): 1150 - 1350 nm (for fibre length 2 m)Limiting wavelength in cable: ≤ 1260 nmAttenuation (client specifies max. value of range): 0,35 - 0,40 dB/km na 1310 nm

0,21 - 0,30 dB/km na 1550 nmSpectral change of attenuation: ≤0,1 dB/km in range 1285-1330 nm

≤ 0,05 dB/km in range 1525-1575 nmLongitudinal homogeneity of attenuation: no point discontinuities > 0,1 dBAttenuation by wavelength of absorbing maximum of OH-iont (1383±3µm) ≤2 dB/km

Chromatic dispersionWavelength of zero chromatic dispersion λ0: 1300 - 1322 nm (typically 1312 nm)Dispersion between 1200 and 1600 nm is possible to calculate according toD(λ) = 0, 25.S0.λ.(1− (λ/λ0)

4)Maximal dispersion by 1550 nm: 18 ps/km.nmMax. decline of dispersion characteristics by wavelength of zero chromatic dispersion:So ≤ S: 0,092 ps/nm2.km (typically 0,088 ps/nm2.km)


Losses inflicted by macro-bending:Less than 0,5 dB at one winding with dispersion 32 mm by λ = 1550 nmLess than 0,05 dB = 1310 nm and less than 0,1 dB by λ = 1550 nm on 100 windings

with dispersion 75 mm.Polarisation mode dispersion: 0,5 ps/

√km by 1310 nm (cable Lucent Technologies).

Mechanical parameters Tension strength (ProofTest): 0,7 GPaTightening force of primary coating: < 8,9 N , ≥1,3 N

Climatic immunityTemperature dependence of attenuation: ≤0,05 dB/km inside range -60 C to +85 CStatic fatigue: Value of coefficient static fatigue is > 20 using protection D-LUX 100R.Preserving of colour marking:Colour marked fibres in primary protection D-LUX 100R do not embody any changes

of colour after following tests of ageing:- 30 days by 95 CO and by 95% relative air humidity. - 20 days in dry heat 125 C

Other characteristicsRelative difference of refraction index: ∆1= 0,33%Effective group refraction index: 1310 nm 1,466

1550 nm 1,467Numeric aperture: 0,12Rayleigh‘s coefficient of backscattering: 1310 nm -49,6 dB

1550 nm -52,1 dBCurving of fibre: halved diameter ≥ 2 m

Single mode fibre with depressed profile of refraction index (DepressedClad, DC)

General characteristicsSingle mode fibre with depressed profile of refraction index is composed by germanium

doped core, outer coating, core, inner coating and coated by pure silicon glass. Schemeof refraction index profile is imaged in Fig.7.7. Fibre is designated for all applications,where low attenuation and broad bandwidth for higher bit rates are required. Fibre isoperable by both used wavelengths, i.e. 1310 and 1550 nm. The other advantages are asfollows:

• Extremely low attenuation for both wave lengths.

• Excellent geometrical parameters enable to reach extremely low inserted attenua-tions of welded splices as well as connectors.

• Doubled primary coating D-LUX 100 secures excellent mechanical and climatic im-munity.

• As the fibre is placed into cable Lucent Technologies, the manufacturer guaranteesexcellent parameters of fibre as well as cable seen by polarisation dispersion. Guar-antee of this parameter is important especially for analogue applications.(CableTV).


• Depressed profile of refraction index secures excellent immunity of attenuation againstall micro- and macro-bending, and also by changing of wave length to 1550 nm.

• As the fibre is placed into cable Lucent Technologies, the manufacturer guaranteesexcellent parameters of fibre as well as cable seen by polarisation dispersion. Guar-antee of this parameter is important especially for analogue applications(CableTV).

Figure 7.7: Profile of refraction index for DC

Geometrical parametersFibreDiameter of core: 8,3 µm (nominal value)Diameter of coating: 125 ± 1 µmExcentricity of core: < 1%Excentricity core-coating: ≤ 0,8 µ m

Primary protectionDiameter of primary protection: 245 ± 10 µmExcentricity. primary protection - coating: < 12µm

Transmitting parameters:Diameter of mode field (MFD): 8,8± 0,5 µm (1310 nm)

9,7± 0,6 µm (1550 nm)Limiting wavelength (λcut off ): 1170 - 1310 nm (for fibre length 2 m)Limiting wavelength in cable (22m): ≤1260 nmAttenuation (client specifies max. value of range): 0,35 - 0,40 dB/km by 1310 nm

0,21 - 0,30 dB/km by 1550 nmSpectral change of attenuation: ≤ 0,1 dB/km in range 1285-1330 nm

≤0,05 dB/km in range 1525-1575 nmLongitudinal homogeneity of attenuation: no point discontinuities > 0, 1 dBAttenuation by wavelength of absorbing maximum of OH-iont (1383±3µ): ≤2 dB/km

Chromatic dispersion


Wavelength of zero chromatic dispersion (λ0): 1310±10 nm (typically 1310 nm)Dispersion between 1200 and 1600 nm is possible to calculate according toD(λ) = 0, 25.S0.λ.(1− (λ/λ0)

4)Maximal dispersion by 1550 nm: 18 ps/km.nmMax. decline of dispersion characteristics by wavelength of zero chromatic dispersion

(S0):0,092 ps/nm2.km (typically 0,088 ps/nm2.km)Losses inflicted by macro-bending:Less than 0,5 dB at one winding with diameter 32 mm by λ =1550 nmLess than 0,05 dB for 1310 nm and less than 0,1 dB by λ = 1550 nm on 100 windings

with diameter 75 mm.Polarisation mode dispersion: 0,5 ps/

√km by 1310 nm (cable Lucent Technologies).

Twice layered primary protection Lucent Technologies D-LUXR100

By choose of suitable optical cable it is important from the user point of view, howattenuation of fibres could be increased due to the various mechanical or climatic im-pacts. Increase of attenuation seems to be often inflicted by micro-bending of opticalfibres. Twice layered primary coating Lucent Technologies D-LUXR100 bars maximallyto arising of microbendings and also by other points of view upgrades quality of opti-cal fibres and cables Lucent Technologies. Primary coating D-LUXR100 is composed bytwo acryllat layers of approximately same thickness applied on fibre in such a way, thatoverall fibre diameter with primary coating 245 ± 10 µ. Inner layer embodies smallerYoung‘s elasticity module and creates something like pad protecting fibre against outerinfluences together with prevention of arising micro-bending. Outer layer with higherYoung‘s elasticity module protects better fibre against influence of outer factors.

Advantages of twice layered primary coating Lucent Technologies D-LUXR100:

1. Minimising of micro-bending. Soft inner layer of primary coating enables to fibrerelatively loose placing and eliminate by this inflicting of outer stresses leading tomicro-bending arise. This feature is very important for behaviour of fibre by lowtemperatures.

2. Upgraded immunity against inflicting of outer stressing.

3. Easy removal of coating off fibre (for welding or connectoring).

4. Excellent stability and long lifetime of fibres.

Twice layered primary coating Lucent Technologies D-LUXR100 is designed in such away to be as far as immune against degradations inflicted as by hydrolyse as oxidation.Fibre with mentioned primary coating performs excellent stability of parameters and longlifetime as in humid as dry environment. All these features secure following advantages:

• Colour marking does not changes itself during whole lifetime.

• Fibres do not adher mutually.


• Cohesion of primary coating is not changing during whole lifetime as well as strengthneeded for its removal is not significantly changing.

• Excellent immunity of fibres against static fatigue.

Twice layered primary coating Lucent Technologies D-LUXR100 is used by all fibretypes of Lucent Technologies.

7.3 Theory of optical transmission, loss and dispersion

Transmission through optical fibre in case of multi mode light guide is provided by hun-dreds to thousands of modes.

In contrary to single mode light waveguide, which enables only single mode propa-gation of electromagnetic wave of type HE11. For single mode transmission should befulfilled condition, that diameter of core in this case should be comparable seen by orderwith wavelength of used radiation. Diameter of core is in this case substantively smallerin compare with multi mode light waveguide.

Transmission attributes of optical light guides may be investigated using two methods.In case of much larger diameter of core compared to wavelength of transmitted lightenergy, laws of geometric optics are suitably available. This condition is not fulfilled forsingle mode light guides. Second method of solution is derived from wave equations thosewere originated by Maxwell‘s equations.

Compared considerations valid in hollow metallic waveguides, the theoretical investi-gation of dielectric light guides much more difficult, what is inflicted by limiting conditionalongside dividing line core - coating. Respecting these realities solutions are reachedby simplifying assumptions, that light guide is composed of core and coating, there areranged infinitely.

Specific attenuation as well as dispersion are defined as basic transmitting parametersof light guide. Both these parameters are function of light wave length, propagating itselfthrough light guide and are dependent on used material, its purity and geometric andphysical light guide parameters.

Light guide manufactured from silicon glass and dotted for reach of required refractionindex attributes of core and coating, releases light of wavelength 0,5 up to 1,6µm (seeFig.7.8.).

This so called window of passage permeability, is enclosed from site of shorter wave-lengths enclosed by ultraviolet absorption allied with change of electrons energetic levelchanges in glass fibre. Increase of attenuation on site of longer wavelengths is inflictedby absorption of infrared radiation, due to mechanical vibrations of molecules of glass.Limiting of window under hand is given by Rayleigh‘s back-scattering, which decreasesproportional to fourth power of λ. By light guides is low margin of window undulated dueto influence of contaminations, there absorbing light by certain wavelengths. This increaseof specific attenuation is significant by wavelengths 0,95; 1,24; and 1,39 µm, inflicted byOH radicals, these are originated by rests of water molecules contained in core of lightguide. Quantity of water increases attenuation of glass fibres together with decreasing of


Figure 7.8: Loss characteristics of optical waveguide

mechanical strength. In Fig. 7.8 are imaged ranges utilisable for transmission seen byminimal specific attenuation. There are wavelengths 0,8 to 0,9 µm, hereafter around 1,3µm (range of zero dispersion) and by wavelength 1,55 µm.

These narrow ranges are signed as 1st, 2nd and 3rd window. In Fig.7.8. are marked outnewly exploited windows (bands) 4 and 5. Wavelength 1,625 µm is used for supervisingand control systems.

All these parameters influence transmission of signal through lightguide. Loweringof individual components amplitude of signal is inflicted by attenuation and distortion.Most important impact to distortion is due to dispersion. It may be sorted to:

• Material dispersion is dependence of group delay on wavelength, n = n(λ).

• Mode dispersion. This is dependence of group delay of core waves (individual modes)on wavelength.

• Dispersion of group delay. Various order core waves of, ie. various modes havedifferent group delays.

Dispersion characteristic is demonstrated in Fig. 7.9, where actually mostly used fibresare marked.

Fibres as per Recommendation ITU- T G.652 have zero value coefficients of chromaticdispersion in 1310 nm wavelength range and roughly 18 ps/km.nm for 1550 nm. Fibreas per Recommendation G.653 with shifted chromatic dispersion (DSF) is suitable forvery high bit rate systems, but not for WDM operation. Very suitable seems to be


Figure 7.9: Curve of chromatic dispersion

Recommendation ITU-T G.655 with non-zero chromatic dispersion (NZDF), characterisedby low value of chromatic dispersion, but impact four-wave mixing is restrained. This fibresupports implementation of DWDM as well as very high bit rate transmission systems.As proposed trace does not meet attenuation requirements, insertion of repeater or actualnew element - optical amplifier is. Optical amplifier does not require conversion O - E -O exploited by repeaters.

Optical amplifiers (EDFA)Principle of optical amplifier is based on stimulated emission. This energy is supplied

by laser source through coupler to doped fibre EDFA - Erbium Doped Fibre Amplifier.Stimulating radiation excites atoms of active materials, though photon of transmittedsignal may launch stimulated emission. Advantages of optical amplifiers:

• There are independent of bit rate,

• They amplify all types of modulation,

• They amplify all channels of WDM.

Usage of optical amplifiers:

• Link amplifier,

• Preamplifier,

• Power amplifier.

These new trends meet important assert by realisation of long-haul traces.

7.4 Optical cables

Proper core and coating is to be protected against mechanical stress by several millimeterthick protective layer, so-called primary coating and then several tenths of mm secondaryprotection. Of such prepared fibres will be coiled up light guide cable. There is used


so-called loosed secondary protection. Loosed secondary protection of fibres is composedof plastic tubule, in which is laid as one as more fibres. The gel may fill inside space oftubule.

There is necessary to consider these main factors:

• Optical: number of fibres in cable, attenuation by certain wavelength, dispersion oftransmitted pulses, numerical aperture of fibre.

• Mechanical: tension strength, immunity against pressure traversing, bending prop-erties, stamina against abrasion, vibrations and against influence of environment.

• Constructional: material and dimensions of core, coating and protective layers,strengthening materials and their dimensions. Examples of various profiles of opticalcables are introduced further. Classical construction, when fibres are twisted intolayer (layers) around tensile element (Fig. 7.10).

Figure 7.10: Various designs of optical fibre cables a, b, c,...

• Grooved construction where fibres alone or in secondary coating are laid in grooves(Fig. 7.11)

• Ribbon construction where individual fibres grouped by 4, 6 or 12 fibres are com-posed upon themselves (Fig. 7.12) and consequently are cabled. Groups of fibres arecomposed eventually for their higher numbers. Usage first of all in access networks.Actually are available welding machines able for 12 fibre ribbons.

• Also other different cable constructions are known. As tension elements are by sideof cable in contrary to fibres in the centre.


Figure 7.11: Grooved construction of cable

Figure 7.12: RIBBON cable - banded

Examples and basic optical cables characteristics: (firm Lucent Technologies)

OPTION1Full dielectric, dry optical cable.

ApplicationOptical cable OPTION1 (Outside Plant to Indoor Optical Network) is full - dielec-

tric universal (outdoor as well as indoor application) optical cable with dry core inside.Composition of cable OPTION1 is similar to other outdoor cables, due to this fact aresecured required tension and mechanical features for outdoor application. Dry construc-tion of cable core enables to protect cable by non-combustible coating non-containinghalogens (LSZH - Low Smoke Zero Halogen). Therefore is this cable suitable for indoorapplications.

Description of cableComposition of cable OPTION1 comes-out from well known construction Loose Tube.

Optical fibres are protected by tubule of loosed secondary protection, which diameteris several times larger than diameter of fibres. Tubules are filled by special gel more,


which bars water infiltration to fibres together with securing of relatively mechanicalindependence fibre vs. cable. Protective tubules are easy identifiable thanks to colourmarking.

Tubules are winded around central tension element. In contrary to common cabletypes Loose Tube the core is not filled by gel, but anti-humidity protection is secured bydry bands impregnated by material called SAP (Super Absorbent Polymer). Absenceof gel inside the cable simplifies preparation of cable before jointing.

Needed tension stamina is secured by hosiery yarn (aramid) placed under the cablecoat, which is manufactured from LSZH material. Optical cable OPTION1 meets allrequirements for outdoor as well indoor cables. Optical cable OPTION1 is very suitablefor such traces, where cable crosses dividing line of outdoor/indoor rooms. Thereforeinstalling costs are reduced significantly, while change between two types of cables isavoided.

Features

• Optical cable for indoor/outdoor applications with capacity up to 144 fibres.

• Full dielectric construction.

• LSZH coat immune against UV rays.

• Absorption SAP bands barring infiltration of water alongside cable are inside.

• No change of cable type by passing dividing line between indoor and outdoor envi-ronment.

• Technique of reversed oscillation ROL used for tubules twining by cable manufac-turing enables easy access to fibres and simple jointing.

• Ripping cord simplifies removal of individual layers of coating.

• Cable is able to operate by temperature range - 40 to 70C.

• Optical cable OPTION1 meets all requirements for outdoor as well indoor cables.

• Dry composition of cable core makes installation as well as maintainance effective.

• Low weight of cable enables further reduction of installing costs. (blowing-in,pulling-in, transportation,. . .).

• Manufacturer is a holder of quality certificates ISO 9001 and Bellcore CSQP.

Notation of cable for orderingAT - S1, S2, SF , S3, S4, S5, S6 - Number of fibres up to 144S1- Operational wavelength1 = only 1310 nm2 = equal attenuation as by 1310 as 1550 nm3 = attenuation by 1550 nm minus 0,1 dB/km than for 1310 nm


6 = 1550 nm (TrueWaveTM fibre)R = transmission on 850 and 1300 nm (multi-mode fibre)

S2 - Maximal attenuation to 1310 nmConventional single-mode fibreB = 0,35 dB/km4 = 0,40 dB/kmDispersion shifted fibre (TrueWaveTM vlkno)2 = 0,25 dB/km (1550 nm only)3 = 0,30 dB/km (1550 nm only)Multi-mode fibreS = 3,5/1,0 dB/km 160/500 MHz.km (min. transmitted band)U = 3,4/1,0 dB/km (850/1300) 200/500 MHz.km (min. transmitted band)

SF - Type of fibre0 = Lucent DC (Depressed Clad) M = Lucent MC (Matched Clad)D = Lucent DS (Dispersion Shifted SMF)9 = 62,5/125 µm Multi-modeT = TrueWaveTM fibre

S3 - Dielectric central element1 = D-P

S4 - Tension strength2 = 2700 NSs - Solution of fibre protectionO = OPTIONl Loose Tube

S6 - Number of fibres per one tubule2 = 2 fibres4 = 4 fibres6 = 6 fibres8 = 8 fibresN = 10 fibresT = 12 fibres

Notes:P = Non - inflammable coatD = Dielectric tension element

POWERGUIDE TMFull - dielectric self-contained optical cable

Application: Optical cable PowerGuide (TM) is full - dielectric self-contained opticalcable suitable for distances up to 100 m between masts as well as braces. Thanks to itsconstruction, which secures high immunity against weather influence and regarding to easyinstallation with minimised costs, optical cable PowerGuide (TM) performs advantageouschoose for by catenary hanged optical traces.

Description:


There is utilised fully proved and highly reliable protection Loose Tube, known fromconstruction of out-door cables. Optical fibres are protected by tubule of secondaryprotection with several times larger diameter in compare with fibre one. So tubule maycontain several fibres. Tubules are filled by special gel against water infiltration to fibres.Relative mechanical independence of fibre and cable is secured. Tubules are windedaround central dielectric tension element. Protective tubules are easy identifiable thanksto colour marking. Needed tension stamina is secured by hosiery (aramid) yarn placedunder the cable coat; using this cable are eliminated needed auxiliary carrying elementsknown of construction of other cables. Optical cable OPTION1 meets all requirementsfor outdoor as well indoor cables. Optical cable OPTION1 is very suitable for such traces,where cable crosses dividing line of outdoor/indoor rooms. Therefore installing costs arereduced significantly, while change between two types of cables is avoided. Small diameter,slippery radial form and integrated tension elements secure high immunity against weatherinfluences, as wind or ice, reduce sagging of cable and load of masts.

Features:

• Easy installation.

• Each cable is manufactured customised for individual applications.

• Distance between masts up to 100 m.

• Proved technology of Loose Tube protection.

• Cable is manufactured up to 144 fibres.

• Technique of reversed oscillation ROL used for tubules twining by cable manufac-turing enables easy access to fibres and simple jointing.

• Tension elements are manufactured of dielectric aramid (kevlar) hosiery yarn.

• Ripping cord simplifies removal of individual layers of coating.

• Manufacturer is a holder of quality certificate ISO 9001.

Installation:Optical cables PowerGuide TM may be hanged on masts of power supply distri-

bution network being immune against electromagnetic influence onto transmitted signal.There is not necessary to interrupt power supply during process of hanging. Installationmay be done quickly and without complications also by dense urban areas.

• Low installation cost.

• Easy installation.

• There is not necessary to interrupt power supply.

• Quick and simple installation densely populated areas.


Figure 7.13: Cable OPTION1

Figure 7.14: Self-contained optical cable

Optical cable of Mini-LXE type

General characteristics:Cables of Mini-LXE type are lightened and constructively simplified version of cables

LXE (Lightguide Express Entry). Their core is performed by single central polythenetubule of outer diameter 3,9 mm. Tubule is gel filled and may contain up to 3 bundlesper 6 fibres, therefore maximal 18 fibres. Each fibre bundle is held and identified togetherby coloured file. Colour differed are also individual fibres.


Mechanical protection of cable is secured by armour (corrugated waveguide) fromchromium-plated steel and two steel tension elements. This combination secures tensionstrength 1800 N, which is sufficient for major part of installing methods. Outer coatingof cable is made from Middle Dense Polythene (MDPE).

Cable Mini-LXE performs economical and space saving solution for all optical net-works, not requiring higher numbers of fibres. Its applications are to be found first of allin access as well as Cable TV networks.

Cable Mini-LXE is fully compatible with other accessories supplied by Lucent Tech-nologies (splices, cabinets, distribution frames,...) and enables complex end-to-end solu-tion of optical network.

Recapitulation of basic features of cable Mini-LXE type:

• Optimised cable construction for max.18 fibres.

• Coloured marking of fibres as well as fibre bundles (6 fibres in one bundle).

• Core of Light-pack type (single central tubule with fibres), coat of LXE type (steelarmour + two steel tension elements).

• Small diameter and low weight by tension strength 1800 N - simple and very quickaccess to fibres.

• Available with fibres DC (Depressed Clad) or MC (Matched Clad) types.

• Primary protection of fibres D-LUX 100 affords excellent mechanical and climaticstamina to fibres as also as to cable itself.

Figure 7.15: Optical cable Mini-LXE


Indoor optical cable of ACCUMAX typeIndoor optical cable of ACCUMAX type is applicable for practically all indoor usage

due to its excellent mechanical attributes non-requiring higher number of fibres. There isapplicable for cable room - exchange connection. This cable is jointed there to outdoorcable in optical main distribution frame or directly connected to transmission equipment.There is very suitable for FTTD (Fiber to the Desk).

Cables of ACCUMAX type contain single-mode optical fibres protected by doubledprimary coating D-LUX φ 100 and close secondary protection with outer diameter 0,9mm. Fibres may DC (Depressed Clad) or MC (Matched Clad) types. Identification offibres is secured by colouring of close secondary coating. Maximum of optical fibres incable ACCUMAX is up to 72. Optical fibres are surrounded by kevlar (aramid) fibres,there provide tension stamina and mechanical strength. Outer coat of polyvinylchlorideis yellow.

Parameters:Type of fibre: Lucent Technologies SM DC or SM MCPrimary coating: D-LUX 100 Ø245 ± 10 µmDiameter of close secondary protection: 0,9 mmAttenuation of fibre: 1310 nm ≤0,4 dB/km

1550 nm ≤ 0,3 dB/kmChromatic dispersion: 1310 nm ≤ 2,8 ps/km.nm

1550 nm ≤ 18 ps/km.nmLimiting wavelength: ≤1230 nmOperational temperature: −20C ÷+ 70C

Installation of optical fibres and cables

Actually mostly used method of optical fibre splicing isWelding

• technology of electric arc welding is done by one-purpose welding half-automat ofmicro-computer controlled automat. Tests of tension strength and measuring of at-tenuation follows completing weld. There is necessary break the splice in case of anydeficiency and renew whole process: remove coatings, crank the fibre, clean splicetails and fasten them into aligner of welder. More detailed in script Transmissionmedia - laboratory exercises. Connectors are used in facilities, where cables are ter-minated. Connectors require sophisticated manufacturing process due to necessaryprecision. Completion of optical traces are done by:

• laying of buried cable,

• laying of cable into polythene tube,

when overwhelming method is ”blowing in’ polythene tube. Roughly 2 up to 6 km ofoptical cable length is possible to blow in.

Machines for classical mechanical pulling should be equipped by control of pullingforce and eventual automatic stop in case of damaging danger of optical fibres.


Very actual novelty is ”grooving” method. Being developed by Siemens, MCS -(Micro Cabling Systems) - enables economical dug-less laying of optical cables.

First method (MCS-Road) enables cable laying into the road-way or pavement intothe groove only 6 to 10 cm under surface. Therefore may be excavations avoided as wellas cable laying to the depth 60-80 cm. Specially developed cable is equipped by coppertube.

Second method (MCS-Drain) exploits for cable-laying drains of outfalls. Both con-ceptions are mutually compatible. Advantages: Quick progress of cable laying, dramaticreduction of excavations costs, minimal inflictions of transport and environment.

Optical joints and distribution frames belongs to cable accessories.

Figure 7.16: Indoor optical cable

Examples:1. Optical joint (armature) type 2500 LGOptical joint type 2500LG is individual optical joint for universal usage. Its cover is

made from reinforced thermoplastic, which provides very good mechanical, climatic andchemical protection. Joint is in basic design equipped by three cassettes for storage ofwelded or mechanic splices of optical fibres. The joint equipped by these cassettes is ableto store 24 splices. Optional is possible to place one extending cassette D-182563 inside.Using this cassette it is possible to place there 3 cassettes type UC-54. These cassettesenable extend joint capacity 54 welded splices using mechanical sandwich protection ofthese splices. All components needed for assembling of two cables (10÷ 21, 6 mm) is inbasic package. The only consumption material, which is to be ordered separately, is fillingmass, so-called Encapsulant, by which is filled bottom of armature against infiltration ofwater.

Basic features and parameters:

• Universal usage (SC).

• Capacity 24 splices of optical fibres, using extending cassettes to 30 or 54 splices.

• Optional possibility of mechanical splices.

• Welded splices with thermo contractible weld protection.


Figure 7.17: Optical joint

• Welded splices protected by sandwich weld protection.

2. Optical distribution framesOptical distribution frames of LGX series are assigned for termination or mutual

interconnection of optical cables inside building. Distribution frames create together withtheir accessories modular easy extendable box of bricks. There are possible to be placedinto 19” 21” (ETSI) or 23” rack, eventually to be fastened directly on the wall. Groundstone of LGX series are individual racks. As to their function are these racks sorted into:

• Terminating - designated to direct termination of fibres in connectors.

• Free laid for splices - serves to laying of welded fibre splices and their reserves as bypigtail welding as by direct fibre welding of different cables.

• Laying for connecting modules (storage) - serves to laying of surplus length of con-necting optical modules.

• Combined (combination) - serves as combination of laying and terminating rack.

They enable welding of pigtails and their termination on connector boards. Capacityof single racks may be 24, 72 or 144 fibres. Their width is 43,2 (17”) cm and depth 27,9cm (11”). Height varies as to the type among 12,7 cm (5”) to 53,4 cm (21”). Somedistribution frames are installed in transmitting media laboratory.


Figure 7.18: Optical distribution frames

7.5 Practical usage of optical fibres for high bit rate transmis-sion

General awareness of experienced telecommunication specialists has been firmed into fixedidea concerning unlimited capacity and quality of long hauled or transport networks. Thisopinion was supported by dramatic development of optical networks. Increasing numbersof operators, new ring topology (security and reliability upgrade) support this opinion.Realised transmission capacity was evaluated as over-dimensioned. Reality of last twoyears turned it into other dimension. Quick exhausting of capacity is given by stormydevelopment of computer networks and their enlargement into worldwide dimensions.Growth of data transmission rises approximately 35% a year in compare with telephoneoperations (8%). Next upgrade is connected with installation of subscriber data loops,which may inflict access networks overloading. Even if multi-mode are sufficient for nu-merous applications, change for single-mode ones will be necessary in plenty of cases.Concluding this introduction we may state, that transmission using single-mode fibres isnot unlimited and in some cases becoming fully loaded. How to continue?

Methods of transmission capacity upgradeThere are three possibilities to be recognised:

• fibre multiplex, or enlargement number of fibres in given trace (reserve tubes); forextreme long traces (submarine cables) difficult realisable,

• increasing of bit rate as well as modulation velocity is mostly used method tosolve this problem. There was possible to upgrade (in SDH - Synchronous DigitalHierarchy, e.g.) bit rate 155 Mbit/s (STM - 1), across 622 Mbit/s (STM - 4) upto actually most utilised bit rate 2,5 Gbit/s (STM - 16). By transmissions over 2,5Gbit/s chromatic and polarisation mode dispersion of optical trace become as limit-ing parameter for conventional single-mode fibres beyond attenuation. By upgradeof bit rate from 2,5G to 10 Gbit/s maximal range of trace will be reduced to the


value 0,063 1. Arising problems of chromatic dispersion may be compensated usingsource with extremely small spectral halved bandwidth, eventually compensate byspecial techniques (insertion of compensating fibre or Bragg grid).

• Very perspective method has been introduced in WDM (Wavelength DivisionMultiplexing) utilising parallel transmission of more wavelengths through singleoptical fibre. So transmission of bit rate 2,5 Gbit/s using four wavelengths enablesupgrade to parallel sovou kapacitu na 4*2,5 Bbit/s. This idea is not completely new,but as lately as thanks to newly developed technologies these means of transmissionhave been introduced into service within last years. There is to be supposed, thatthis technology will become important asset not only from optical transmission pointof view. We will be involved in this perspective method as follows.

Realisation of wave multiplexes

First of the simplest solution offered by manufacturers is WDM exploiting two wave-lengths, as 850 nm with 1300 for multi-mode fibres or 1310 and 1550 nm for single-modefibres. System enables as full duplex using single fibre only or doubling of capacity. Butthis is not perspective solution seen by perspective outlook. This method uses only so-called ”attenuation windows”.

Much more perspective solution lies in exploitation of highly selective radiation sources,where four wavelengths may be transmitted in third ”window” (minimum of attenuation).An example of multi-wavelength is imaged in Fig. 7.19.

Figure 7.19: Scheme of optical link with wave division multiplex

This way was prepared by new technological findings, there enabled realisation ofspectral spacing of individual channels less than 1 nm. There was invention of laser withso-called DFB (Distributed Feed-Back) or laser with Bragg‘s grid. These lasers performsource of extremely pure radiation spectrum characterised by extraordinary narrow spec-tral line. Lasers offering spectral half-line of order 5 MHz , i.e. 0,000 04 nm for 1550nm are available actually. They perform excellent dynamics together with possibility ofprecise wavelength adjustment.

Number upgrade of wavelengths opened the process to introduction of so-called DWDM- Dense Wavelength Division Multiplexing. This progress accelerated also standardisingwork in International Telecommucation Union (ITU). Ready Recommendation G.692


defines standards for these transmission; as basic spectral channel was chosen wavelengthof krypton spectral line of frequency 193,1 THz. Other spectral channels spaced 100GHz one of another were derived from this frequency. Systems with dense spacing of50 GHz are commercially available and the narrower spacing up to 25 GHz is in closeoutlook. Spectral channels and their spacing were defined in frequency scale and for theircalculation as wavelength following relation is for disposal:

∆λ = λ∆f/f = λ2∆f/c

where c is light velocity in vacuum (2,99792458 x 108 m/s). Then for wavelength 1550nm spacing of channels ∆f = 100 GHz equals on wavelength spacing approximately ∆λ= 0,8 nm.

Exploitable technologies: multiplexers and de-multiplexersAs it is evident from Fig. 7.19, for mergence of wavelengths is utilised multiplexer, in

the output then de-multiplexer. Wave multiplexer mixing more wavelengths into singleoptical fibre may be simply realised as fibre splitter with some inputs and single com-mon output. For higher channel numbers are used multi-spectral sources with tuneablewavelength.

Realisation of de-multiplexer is more complicated, while dispersion element is to beused, as diffraction grid, prism or optical filter.

Optical filters are used for lower wavelength numbers; this is advantageous also seenby costs. Diffraction methods are unavoidable for higher wavelength numbers. Insertionloss is varying between - 35 up to - 50 dB. The solution of spectral de-multiplexer based onintgegrated optics with phase series of waveguides (AWG - Array Waveguide Grating).

Two-wave multiplexAbove mentioned simple wave multiplex for full duplex purpose, eventually for dou-

bling of transmitting capacity is imaged in Fig. 7.20.

Four-wave multiplexasto poptvan multiplex pro rychl zven kapacity st i za pomrn nzkch nklad. Zaloen na

principu kaskdnch interferennch filtr s odstupem 8 nm (viz obr. 7.21).

Hust vlnov multiplexy (DWDM)There is often enquired multiplex for quick upgrade of network capacity by low costs.

Its principle lies in cascaded interference filters spaced 8 nm (See Fig. 7.21).DWDM - Dense Wavelength Division MultiplexersLucent Technologies, Alcatel, Nortel, NEC, etc. are most prestigious manufacturers of

DWDM. DWDM providing 16, 20, 40, 60 up to 100 spectral channels are actually offered.Let us perform equipment Wave Star OLS 806 of Lucent Technologies. It exploits 16wavelengths, by-passing attenuation 33 dB, i.e. it is equal to distance 120 km withoutbleamplifying. (True Wave - non zero dispersion fibre is supposed). There is possible to usethis equipment for ring topologies composing, as it is evident from Fig. 7.21.

Influences to quality of WDM transmissionFor secure of quality transmission is necessary to meet appropriate limits, there are

verified by measurements. These are as follows:


Figure 7.20: Wave multiplex (Coupler)

Figure 7.21: WDM JDS FITEL (1533/1541/1549/1557 nm)

• Central wavelength, which is obliged to meet appropriate standards; precise mea-surement should be secured also regarding temperature changes, non-stability oflaser, back reflections;

• Bandwidth shall meet criteria of spectral characteristics;

• Insertion loss shall secure most suitable most favourable transmitting conditions;

• Crosstalk, as former by metallic conductors, crosstalk between neighbouring wave-lengths shall meet by DWDM installations limits. Also crosstalk through non-linearity inflicts quality of transmission;

• Back reflection may differ in individual channels and its value is necessary to bekept in needed tolerance due to the stability of system.

• Very important separate item is type of used fibre.


Figure 7.22: OLS 806 in ”ring application”

An example of spectral characteristics of four-wave multiplex is imaged in Fig. 7.23.

Figure 7.23: WDM spectrum

Choose of fibre type is able to be accommodated to supposed introduction of DWDMsystem. This principle is actually realised by investments of alternative operators trans-port networks using so-called ”Tele-houses”.

Significantly arduous situation is by future need to utilise existing laid fibres forDWDM operation. First of all older fibres (ITU-T G. 652) seem not to be optimal forDWDM. Relatively large chromatic dispersion in light wave band 1550 nm limits rangeof link and its compensation is necessary for longer traces.

The range of link is possible to increase by insertion of optical amplifiers, see Fig. 7.24There are so-called EDFA (Erbium Doped Fibre Amplifier), there amplify any optical

signal. Its insertion inflicts other non-linear effects, first of all Four Wave Mixing - FWMand Self Phase Modulation - SPM.

Also values of Polarization Mode Dispersion - PMD shall meet inside tolerance limits.All above mentioned influences inflict transmission and there are to be respected by designof networks.

Exploitability of wave multiplexes in academic computer network


Figure 7.24: Scheme of optical amplifier

One of very first applications is introduction of two-wave multiplex into experimentalnetwork TKO. System performs its functionality, enables element measurement and therewas realised demonstration for supervision of optical cable. Its scheme is in Fig. 7.25.

Figure 7.25: Realisation and scheme of WDM in UTKO network

Introduction of 4-or maybe 8-wave multiplex is considered in Brno network. Prelimi-nary works to introduce experimentally DWDM onto link Praha - Brno - Olomouc. As tothe fact, that older type of fibre is for disposal, compensations methods should be applied.

Further perspectives of wave multiplexes - DWDMBit rate upgrade will perform the trend of further development. Maximal channel

number raise up to 128 or 160. Experimental works reached up to 1024 channels. Nextparallel bands C and L. The universality of transmitting media is upgrading, as for Gbit10 Gbit Ethernet or STM-64.

The upgrade of bit rates up to 20 Tbit/s may be to awaited, while systems with 1,6Tbit/s are introduced actually into backbone networks. As to the distance, using principleof Raman type of diffusion and soliton transponders, the range of DWDM systems maybe enlarged up to thousands of km. Optical cross-connects will upgrade significantlyflexibility of networks. They will enable reconfiguration and back-up of spectral channels


in time of several ms. Actually are realised these elements as cross-connecting matrix1024 x 1024, where all connecting operations are done in the chip using electromechanicalmicro-mirrors and switching is 16 times faster in compare with actual electronic switches.New conception of network is now formed using these elements permeating switching withtransmission into single process back to networks with circuit switching. Concluding thisitem we are able to state, that these new technologies shift significantly offers of newservices as well as transmitting chances of optical telecommunications.

7.5.1 Optical access networks

Thanks to permanent development of technologies as well as offered telecommunicationservices requirements for bit rates of access network connecting terminating point of net-work, i.e. end user to service provisioning telecommunication services. Some subscribersrequire bit rates of hundreds Mbit/s or up to order Gbit/s. Permanently developing op-tical technologies and investment into Optical Access Network - OAN offer provision ofsuch needed broad band.

Even if optical technology was prior to backbone and metropolitan networks, alreadyjust now it is evident, that prospectively seen they will become standard for access net-works too. Optical network will expand from backbone networks up to end user. Thereis expansion of optical fibre into so called ”last mile”.

Basic functional units creating optical access network are as follows:

• Optical Link Termination - OLT securing functions of network interface betweenaccess network and telecommunication services provisioning network,

• Optical Distributing Network - ODN - there is a set of optical transmission meansbetween OLT and ONU,

• Optical Network terminating Units - ONU intermediating functions of interfacebetween optical and metallic section of access network,

• Optical Terminating Units - ONT intermediating functions of subscriber interfacebetween subscriber terminating equipment and access network (Voice over InternetProtocol - VoIP, video, data).

Figure 7.26: Block scheme of access network


Seen by placement of network terminating units ONU in optical access networks andby their design, i.e. in accordance with placement of optical fibre termination are sortedvarious types of optical access networks OAN, of them are usually mentioned as follows:

• FTTC (Fibre To The Cabinet), optical fibres are brought to subscriber cabinet,where terminating points of network are connected to by metallic network,

• FTTB (Fibre To The Building), optical fibres are brought to building; individualsubscribers are then connected by internal network,

• FTTO (Fibre To The Office), optical fibres are brought to business subscriberoffice with enormous requirements for transmitting capacity,

• FTTH (Fibre To The Home), optical fibres are brought to subscriber socket.

Main function of access network is provisioning of transport services in full duplexregime. Transport of signal may be secured by several methods:

• Simplex with SDM division (Space Division Multiplex), transmission is realisedalong two fibres separately for each direction,

• Duplex with WDM division (Wavelength Division Multiplex), transmission is re-alised along single fibre for both directions. Downstream uses wavelength 1550 nmand upstream 1310 nm

• Duplex with FDM division (Frequency Division Multiplex), for transport of signalsin both directions is used only one fibre as well as one wavelength; direction oftransmission is frequency divided.

Parameter assigning character of access network corresponds to the type of transmis-sion tracts exploited in distribution section of network:

• P2P (Point-to-Point), as direct connection of OLT and ONT e.g.,

• P2M (Point-to-Multipoint), passive optical network e.g.

Optical networks are sorted in accordance with character of optical elements and unitsused by distribution of optical fibre into two basic groups:

• AON (Active Optical Network) exploits active optical elements in its distributionnetwork (amplifiers, active splitters)

• PON (Passive Optical Network) utilises only passive elements.

Active optical network AONThere is access network exploiting active network elements for connecting OLT units

with units ONU. AON uses digital equipment generally. Access network seems to berealised by SDH (Synchronous Transfer Hierarchy) configured in ring topology.

AON performs basic infrastructure of so-called hybrid networks, where other technolo-gies are coupled with optical part in higher layers. STM-n signals are used. Secondary


Figure 7.27: Block scheme access network AON.

network levels (xDSL, PON, etc.) are coupled with OAN by synchronous ADM (Add-Drop Muldex) across terminating unit SMT, see Fig. 7.27

Key advantage of active access networks AON is realisation of remarkable larger rangesor bridging of distances between units OLT and ONU in compare with by passive opticalnetworks PON and possibility to use larger dividing ratios in distributing points. Theselarge distances are reached by insertion of active elements (amplifiers, splitters, muldexes)into distributing optical network. This fact meets key disadvantage - necessity of powersupply. Minimising of operational expenses (OPEX) shadows all before mentioned advan-tages, and therefore are mostly used passive access networks PON, first of all for FTTHarchitecture.

Passive optical network PONThis network infrastructure is based on exploiting optical network elements. Techni-

cal means for PON completion was developed in university labs financially supported byLucent Technologies. Distribution network between OLT and units ONU or ONT is com-posed by only passive elements. Considerable expenses reduction as for access networkbuilding up as significant cost reduction for subscriber loop would be reached by PONtechnology keeping all advantages of optical communication. Access networks PON be-come available economically also for residential sector. They penetrate also into so-called”last mile”, what predestines them for implementation in FTTH (Fibre To The Home).

PON networks are mostly realised as link p2mp see Fig. 7.30 c), where transmittingchannel is shared by several users. This method performs the cheapest solution as for op-erator (expenses for connecting of subscriber), as for subscriber himself (taxes fo services).


The only disadvantage seems to be independent sharing of transmitting bandwidth. Incase of demand for large bandwidth of transmitting band, the direct connection betweenOLT and ONT is chosen. (p2p) see Fig. 7.30 b). This method is indeed much more ex-pensive in compare with method mentioned before due to no division of expensed amongmore subscribers is available.

Optical signal in PON networks (p2p) is distributed by splitters, there are passablein opposite direction too, that means they are able to link together signals coming fromsubscribers. There are passive elements dividing only optical signal into demanded numberof downstream without any adaptations, including signal amplification. Bi-directionaltransmission may be realised as by independent fibres as actually by wave division WDM(Wavelength Division Multiplex). So the transmission of optical signal is realised bysingle optical fibre. For downstream wavelength 1490 nm is used, for upstream 1310 nm.Downstream transmission is organised by such a scheme, that each termination unit ONUobtains full multiplexed TDM signal from unit of link termination OLT, of which is ableto choose its own channel, see. Fig. 7.28.

Figure 7.28: Downstream transmission scheme between OLT and ONU units

Upstream transmission uses method of time division multiplex TDMA (Time DivisionMultiplex Access), when each unit ONU inserts its frames into time slot and sends theminto OLT, see Fig. 7.29.

Figure 7.29: Upstream transmission scheme between ONU a OLT units

Infrastructures of passive optical networks are used mostly for distribution of signalin star, ring or bus topology, see Fig.7.30.


Figure 7.30: Topologies used in PON networks, a) bus, b) p2p, c) star, d) ring

These topologies may be combined arbitrary by realisation ODN (Optical DistributionNetwork) respecting features of used optical interfaces OLT and ONU. There is neces-sary to respect several factors designing PON networks. We do come out first of all frombridge-over attenuation of optical interfaces OLT and ONU; we must respect types andnumbers of splitters, switching parts, connectors and features of used optical fibre. Vari-ous conflicts in upstream may come on by timesharing of media due to mutually differentdistances between ONU and OLT units. These conflicts may be avoided by inserting ofprotective timeslot between individual time channels. Its magnitude shall be longer thanmaximal difference of propagation timeslots, it depends on difference between nearest andoutmost unit ONU.

FTTH exploiting PON networks utilise first of all p2p connection, which is providedto those subscribers, who require high transmission bit rates and p2mp, when opticalfibre is shared by more subscribers. This method is much cheaper as for users as serviceproviders. On the other hand this solution provides lower transmission bit rate.

Specification of PON networks for FTTx systemsSeven world leading telecommunication operators established association named FSAN

- Full Service Access Network in 1995, goal of it was defined standardisation and deploy-ment of PON networks, see. Table 7.1. These specifications were designed in such a wayto provide worthwhile broadband services to users as audio, data and video transmission.Following bandwidths were designated by FSAN: 1490 nm for transmission of audio anddata from network to user, in opposite direction is used bandwidth 1310 nm. For videoin downstream was designated bandwidth 1550 nm.


Table 7.1: Parameters of passive optical networks single specification

APON, BPONRecommendation G.983.1 APON (ATM Based PON) was approved by ITU-T (In-

ternational Telecommunications Union-Telecommunication Standardization Sector) in 1998.There is passive optical network, which exploits ATM - Asynchronous Transfer Modefor information transmission. Bit rates are offered in two variants: symmetric service bitrates 155,52 Mbit/s and asymmetric service in downstream 622,08 Mbit/s and back inupstream 155,52 Mbit/s again.

Symmetric service was supplementary added by bit rate 622,08 Mbit/s. ITU-T ac-cepted Recommendation G.983.3 BPON (Broadband PON) in 2001 extending previousstandard and uses equal bit rates. One or two optical fibres in accordance with G.652 areused as transmission media. Bi-directional communication through single fibre is securedby wave division.

GPONITU-T approved specification G.984.1 GPON - Gigabit Capable PON in 2003, ex-

tending generally specification G.983.x. First of all there is extended specification G.983.1as to the bit rate saving principles of access broad band system. ATM cells are used fortransmission, but also method GEM (GPON Encapsulation Method) is available for thispurpose. This method uses GPON frames for transmission, there have variable length ofATM cell as well as GEM frame or their fragments are transmitted together in frameswith fixed length 125 µs. This enables exploiting of packet-oriented services as Ethernetor IP (Internet Protocol). Transmission bit rates are offered in two variants: symmetricservice with bit rates 1244,16 Mbit/s, 2488,32 Mbit/s and asymmetric service in down-


stream 1244,16 Mbit/s, 2488,32 Mbit/s and oppositely in upstream 155,52 Mbit/s, 622,08Mbit/s and 1244,16 Mbit/s.

EPONIntroduction of Ethernet into access networks was secured by acceptance of specifica-

tion IEEE 802.3ah. This specification are marked as EPON - Ethernet Based PON)or also EFMF - Ethernet In First Mile Fibre. Introduction of Ethernet standard up touser and then simplifying of local network coupling was its goal. Ethernet frames of fixedlength 2 ms are exploited for both directions. EPON is designed for multipoint networksharing transmission media, but also communication P2PE - Point To Point Emulationis targeted. Two types of interface are specified by standard IEEE 802.3ah, there differson of other by dynamics and optical power. Type 1000Base-PX10 is designated for usagefor distances up to 10 km with maximal splitting 1:16. Type 1000Base-PX20 is desig-nated for usage for distances up to 20 km splitting up to 1:32. Transmission bit rate wasappointed up 1244,16 Mbit/s symmetric.

Figure 7.31: Transmission bit rates offered to user by symmetric services split 1:32

7.5.2 Triple Play services in FTTH systems

Actual trend of telecommunication operators and providers of broad band services isoffering possibility to user as far as the largest bandwidth and first of all coupled serviceswith it. Permanently intensified competence together with securing of own profitabilitylead implementation of new services. One of them is Triple Play Service”. There is newgeneration of services offering transmission of voice, data and video. These services maybe sorted into basic services and extended services, see Table 7.2. Basic services are notcharged individually, but they are comprehended all-inclusive with provision of broadband service. Super standard services extending basic services are charged.


Table 7.2: Basic and extended Triple Play services

Methods of video signal distributionActual main trend of telecommunication operators is provisioning of video and voice

services broad offer. This is nothing strange - these services will secure dominant part oftheir income. Therefore their drive is focused not only into introduction of new services,but also to searching for most suitable transmission method, which will be able to providemore services together without additional upgrade of transmission band and so increaseoperator‘s income. Video services offered in Triple Play are distributed to users exploitingtwo methods: by so-called overlay PON (video overlays passive optical network) or byIPTV (TV over Internet Protocol).

Overlay PON networks, see Fig.7.32, use wavelength 1550 nm for video transmission,which was reserved for this purpose by ITU-T. Signal is transferred to user by singleoptical fibre together with data stream (data and voice), for which is reserved bandwidth1490 nm using wave multiplex WDM. Transmitted signal may be as analogous as digital.In user site in ONT unit is video signal dropped (by so called triplexer) and transformedinto radio-frequency signal. This signal, in case of classic analogous signal, is led fromONT unit by coaxial cable directly into TV-set. In case of digital signal the Set-top box(STB) is to be used, which transforms digital signal into analogous one. Overlay networkoffers flexibility to providers and enables them to provide broad service offerings. Thesenetworks are able to offer for residential users capacity over their real demands.

Second option for video services distribution in PON networks is IPTV, or switchedvideo. Video signal is transmitted to user using packet switching network in this case.Video signal is digitalised first in the site of network termination and consequently com-pressed. Binary data are encapsulated into IP data-grams. Signal so compressed istransferred to ONT together with data stream (data and voice) exploiting wavelength1490 nm by ATM cells or Ethernet frames. Set-top box with IP interface is inserted intotransmission link between TV set and ONT unit. Interconnection of such IP-STB withONT is realised by structured cabling CAT-5. TV set is connected to STB by coaxialcable.


Figure 7.32: Scheme of Triple Play services processing by systems FTTH (source:EXFO)

Optical splittersOptical splitters are network elements enabling to optical transmitting media be shared

by larger number of subscribers. There are usually bi-directional passive elements inFTTH systems these are operated in PON networks. There are usually bi-directionalpassive elements equipped by single input port and several (2 up to 64) output ports.Downstream signal of OLT coming to input port of splitter is divided into required numberof partial signals. These signals are consequently distributed to individual ONU units.The splitter merges upstream signals coming from single ONU units into one commonsignal, which continues to OLT.

There are passive network elements securing only splitting or merging of optical signalwithout any other conversion. As to the type and manufacturing technology they maywork in defined transmitted band or in its whole bandwidth. The insertion loss is addedinto optical trace value of which depends on input ports number and is indicated in dB,See Table 7.3:

Table 7.3: Inserted loss values for PLC splitter Telcordia GR-1209


Splitters may be sentenced into cascade depending on network topology. Recommen-dations ITU-T concerning inserted loss values using splitters shall be met.

As to the manufacturing technology splitters may be sorted in two groups:

• PCL (Planar Lightwave Circuit)

• FBT (Fused Bionic Taper)

PLC splitters are manufactured by planar technology. Required structure is created onsilicon substrate by technological process. Splitter with up to 32 ports is manufacturableby this technology. This technology is used for splitters with larger number of outputports.

FBT splitters are manufactured by optical fibre splicing by high temperature andpressure. Coating of fibre is fused and cores of spliced fibres come in together mutually.Beams of 2 to 4 fibres are manufactured by this technology, which for higher numberreach composes output ports into cascades. This technology is used for splitters withsmall number of output ports.

Figure 7.33: Exemplification of PLC and FBT splitter structures

Choose of suitable transmitting methodAs it was mentioned before, overlay PON network exploits wavelength 1550 nm for

transmission of video signal to wavelength user, who is separated off data stream, which isso transmitted to user by 1490 nm. This wavelength was not chosen by ITU-T haphazard,but due to the insertion loss value reaches its minimum for this wavelength. While videosignal was originally transmitted, this feature played its decisive role. For securing neededquality of transferred signal it is necessary to secure as far as the largest distance of signalfrom noise CNR (Carrier to Noise Ratio). Minimal CNR value was defined by U.S. FCC(Federal Communications Commission) up to 44 dB. This value guarantees eliminatesso-called ”snowfall” in the picture. But this value used in FTTH systems should behigher than 47 dB; usually 48 dB is used. Actual ONT are able to secure CNR value 48dB by level of received signal -5 to -6 dBm. For securing CNR to meet 48 dB, there isnecessary to use powerful optical sources (lasers, EDFA). So called Brillouin‘s effect, i.e.BS (Brillouin Back Scattering) will perform itself by such light source powers, when partof reflected light ray returns back into light source and inflicts so disturbance.

This scattering emerges due to interactions of light radiation (photons) with virtualgrid consists of acoustics waves (phonons), these are produced by laser source or EDFA


amplifier by huge output powers. This effect was originally observable already by 7 dBm;actually thanks to permanently upgrading technology is this margin shifted behind 20dBm. Optical power was necessary for transmission of analogue signal varies in range of10 to 20 dBm (10 - 100 mV). Choose of power depends on inserted loss of transmissionpath.

Video signal is transmitted mostly in digital version. Not only for this reason availablebandwidth is upgraded several times, but also picture itself performs higher quality anddigital video signal is un-comparably more immune against disturbances. CNR valuefor digital signal transmission is significantly lower and depends on required error rate.Next factor influencing quality of digital video is therefore BER (Bit Error Rate). Forreduction of transmission channel BER are used so called auto-corrective methods asFEC (Forward Error Correction, J.83B). The value of CNR for required error rate 10−9

is 15,5 dB. For transmission of digital video-signal in binary form are necessary muchlower optical power in compare with case mentioned before; powers around 0 dBm onlyare needed. This is done first of all by much lower value of signal/noise ratio. Non-linear attributes of optical fibre may manifest oneself too, as RS (Raman Scattering)e.g. Interaction of photons with silicon grid is reason of this effect. Consequently photonsleft part of their energy and radiation of shorter wavelength is a result of this interaction.Therefore crosstalk may arise between wavelengths in case of wave multiplex. The spacingmin. 0,8 nm between channels shall be kept to prevent this effect.

The advantage of this so-called overlay PON is separation of video signal from datastream by transmission. Transmission bandwidth dedicated to video signal distributionis not influenced by quantity of transmitted data quantity just in this moment. There isnot possible degradation of picture quality by spectral loading of transmission channel.Next advantage is performed by simple Set top boxes; in case of analogous video signalSet top boxes may be excluded at all. Existing network of coaxial cables is exploited byTV signal distribution inside house. These advantages are overlaid by higher expenses forbuilding up as well as operation of this infrastructure. There is necessary to install wavemultiplexes in site of link termination (inside exchange) multiplexing video signal withdata stream in downstream, powerful lasers for video signal and last but not least EDFAamplifiers for this signal. It will perform in user site by expenses for terminating unitONT containing triplexer for separation of individual wavelengths transmitted by opticalfibre.

IPTV or switched video is abbreviation for video signal transmission using packetnetwork. Video data are inserted into IP data-grams and directed to user. Digital videosignal is transmitted together with data stream (data and voice) in this case by wavelength1490 nm. Also there are used relatively low optical powers. Terminating units in usersite ONT are able to meet requirements for CNR 15,5 dB by received signal level -20to -30 dBm (as to the type of receiver); therefore low optical powers of transmitters arerequisitioned. Optical power values varies in range of -1 to 5 dBm; optical powers arechosen inside this range as per bit rate an inserted loss by transmission path. The TriplePla-y method is of complex services provisioning is very economical solution seen as byintroductory investments (CAPEX) as to operational expenses (OPEX). There are notnecessary wave multiplexes and EDFA amplifiers in link terminations in network site as it


is unavoidable by overlay PON. The diplexer only is used in user site termination is ONTunit, what means another cost reduction for service provider. Maybe most significantdisadvantage is transmission bandwidth sharing by video signal as well as data stream.

This method of transmission requires provision of large transmission bandwidth towatch TV and together download large volumes of data. In case of great number TV setsin households and together with demand to watch more TV programs may become, thatvideo signal with higher priority will exploit all available bandwidth reserved for users.Next disadvantage is performed by Set top boxes, these shall support IP interface. Theirprice is relatively high and market offer low. They enable on the other hand simplercommunication with video server in upstream. Not so simple problem for service provideris in connection of new user, especially in case of his demand for more TV sets. Exploitingof existing coaxial distribution network is avoided. while IP Set top boxes are connectedwith ONT unit by structured cabling CAT-5.

Table 7.4: Evaluation of requirements for overlay PON (analogous video) and switchedTV (Digital video) onto transmitting optical powers


7.6 Exercises

A) Optical beam arises from the optical fibre with optical power P=0,1 µW and wave-length λ=1300 nm incident on photo-detector. Determine number of photons inci-dent per one second!

B) Optical fibre is characterised by n1 = 1, 5. Compute NA (numerical aperture) andangel Θ under which light ray may enter the fibre!

8 Appendix

8.1 Exercises results of chapter 3.11

A) I1 = U1/Z1 = 100 mA, a1 = 2, 3 Np, a2 = 20 dB

B) Z =√

(R + jωL)/(G+ jωC) = 1310− j497, γ = 0, 0165 + j0, 0406


A) Capacitance of compound (phantom) circuit is 1,6 times larger in compare withcapacitance of pair circuit.

αk = R2

√C sLpk

= αs = R4

√C.1,6sLps

1Lpk

= 1,64Lps

Llk = 0, 4Lps

B) Open line

Z2 = ∞Reflection factor k = ∞−Z

∞+Z= U0

Uk= 1

U0 = Uk - voltage wave reflects being equally phased and current wave being an-tiphased.

Shortcut line

Z2 = 0

k = 0−Z0+Z

= −1 = U0

Uk

U0 = −Uk the voltage will reflect itself in antiphase, current in equal phase.

8.3 Results of examples

A) C.l = 38, 5.0, 230 = 8, 85nF



A) Photon is a particle with energy defined by relation W = h.v

h = 6, 626.10−34J.s Planck‘s invariable

V= requency of radiation

Energy of one photon W = h.v = h.cλ

= 1, 529.10−19J

Total energy of radiation W = P.t = 10−19J

Within one second stroke on photo-detector N = 10−7

1,529.10−19 = 6, 54.1011 photons.

Note: There is advantageous to express energy of particles by electron-volts, then1eV = 1, 6.10−19J

1J = 6, 25.1018eV

Energy calculated by this exercise is 0,956 eV.

B) from transmission condition

n2 = 0, 99n1

n2 = 1, 485

sinΘ = NA =√n2

1 − n22 = 0, 21 ⇒ Θ = 12, 2o

Result: NA = 0,21 and corresponding angle under which ligth ray is able to enteroptical fibre equals 12, 2o


References

[1] Sobotka, V a kol. Prenosove systemy. Praha, SNTL,1989.

[2] Filka, M. Telekomunikacni vedeni. Skriptum VUT. Brno ES VUT 1988.

[3] Rieger F. Teorie sdslovaci elektrotechniky. SNTL, Praha 1968.

[4] Connor, F.R. Wave Trasnmission.London, Arnold 1972.

[5] Optick0 komunikace. Sbornik prednasek. TECH-MARKET,Praha 2001.

[6] WDM Technology. Firemni literatura EXFO. Quebec, 2002.

[7] Sabella, R., Lugli, P. High speed optical communications. Kluwer AP, London 1999.

[8] Girard. A. Guide to WDM Technology. EXFO, Quebec, 2002.

[9] Hardy. D., Malleus. G., Merur. N. Network. De Boeck. Paris 2002.

[10] Girard. A. FTTx PON Technology and Testing. EXFO, Quebec, 2005.

[11] Jordan, V. Profesionalni datove komunikace - strukturovane a multimedialni ka-belaze.Kassex, Kromeriz. 2005.

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