RESEARCH DEPARTMENT

U.H..:F. TRANSMITTING AERIAL FOR THE WENVOE TELEVISION STATION

Technological Report No. E-l14/12

(1965/38 )

G.B. Millard, B.Se., A.lnst.P. for Head of Research Department

This Report i9 the property of the British Broadcasting Corporation and may not be reproduced in any form without the written permission Qf the Corporation.

November 1965

INTRODUCTION

Technological Report No. E-1l4/12

(1965/38 )

U.H.:F.: TRANSMITTING AERIAL FOR THE WENVOE TELEVISION STATION

A u.h.f. aerial for South Wales has been built as a topmast on the existing 715 ft (218 m) mast at Wenvoe. Space for this aerial was provided by rebuilding the Band I aerial on the support column of the mast. l The new aerial came into service on 12th September 1965.

SUMMARY OF INSTALLATION

Site:

Support Structure:

General Arrangement:

Otannels:

Aerial:

The site is 5 miles (8 km) west-south-west of Cardiff, grid reference ST/111742, height. 422 ft (129 m) a.m.s.l.

The support structure consists of a 715 ft (218 m) stayed mast. Up to a height of 610 ft (185 m) the mast is of triangular cross-section with a side of 9 ft (2'75 m); above this height the cross-section is circular with a diameter of 6 ft 6 in. (2 Ill). The mast is provided wi th three sets of stays on bearings of 84°, 204° and 324° ETN.

See Fig. 1.

The aerial is designed to radiate on four channels simul­taneously. The BBC channels are 44 and 51, of which the latter is used for the opening service. 'The ITA channels are 41 and 47.

The offset on Otannel 44 is pos1t1ve and that on Otannel 47 is negative; Otannels 41 and 51 have zero offset.

The aerial 2 comprises six tiers each of four ~ panels fed with nominally equal amplitude currents in phase rotation, to give a total radiating length varying between 20'~ and 23'~ over the operating bandwidth. The panels are offset on a square of 26 in. (0'66 m) side and are supported by a loaq-bearing glass-fibre cylinder of 5 ft (1'52 m) diameter. Fig. 2 shows the arrangement of the panels inside the glass­fibre cylinder and Fig. 3 shows the construction of each panel.

2

Power:

Templet and horizontal radiation pattern (h.r.p.):

Vertical radiation pattern (v.r.p.):

Gain:

01 ann e I

The arrangement of the distribution feeder is shown schema­tically in Fig. 4. Each half of the aerial is connected to the transmitter by a feeder type F and G 6.1/8 - 50. The mean height of the aerial is 736 ft 6 in. (224'5 m) a.g.l.

Two 25 kW vision transmitters and two will be provided for each channel; for Olannel 51 have been installed.

5 kW sound transmitters at present only those Each transmitter will

be underrun at the power required to give the maximum e.r.p. permitted under the Stockholm Agreement, namely 500 kW.

The service has opened with one vision and one sound trans­mitter fed into each half aerial but at a later date a diplexer and splitting transformer will be added to eliminate differences between the modulation characteristics of the vision transmitters. Similarly, two- and four-channel combining units will be added later, as required.

The h.r.p. was required to be omnidirectional with a max~mum e.r.p. not exceeding 500 kW. The specified tolerance on the h.r.p. uniformity was ± 2 dB. The h.r.p.s at the vision carrier frequency of each operational channel, which are shown in Figs. 5-8, are the mean of measurements made at the contractors test site on each half of the full-scale aerial, i.e. it is assumed that the contributions from each half­aerial add in phase in all directions of azimuth.

The orientation of the aerial was chosen to g~ve the best overall service cover, bearing in mind v.r.p. deficiencies.

The v.r.p. was specified to be gapfilled with the maximum of radiation tilted 0'5 0 below the horizontal. Gapfilling is achieved by means of a phase distribution of the feed currents over the length of the aerial together with a physical tilt of the panels in Tier 1. The v.:r.p.s obtained for each face, shown in Figs. 9-12, were computed from measurements of the amplitudes and phases of the feeds to the aerial panels, taken after erection.

Mean intrinsic gain

41 dB

14'0

44 dB

14'1

47 dB

14'3

51 dB

14'4

Deduct losses

~stribution feeder ~stribution transformer Power in balance load Gapfilling

Mean net gain

0'2 0'1 0'1 0'7

0'2 0'1 0'1

1'1 0'7 1'1

12'9 13:0

0'2 0'2 0'1 0'1 0'1 0'1 0'7 1'1 0'7 1'1

13'2 13'3

Deduct losses

Main feeder, 757 ft (231 m) Feeder ground run Diplexer Splitting transformer

Mean effective gain

H.R.P:· maximum/mean ratio

Maximum effective gain

Programme feed: GPO link.

ACKNOWLEDGEMENTS

1-4 0'2 0'1 0'1 1'8

ll'l --2'1

13'2 --

3

1-4 1'4 1-5 0'2 0'2 0'2 0'1 0'1 0'1 0'1 1'8 0'1 1'8 0'1 1'9 ---

ll-2 ll'4 ll'4 --

1'9 1-9 2'2

13'1 13-3 13-6 --

The mechanical and electrical design, construction and setting to work of the aerial were carried out by the Marconi Co. Ltd. The contracting authority was the BBC Planning and Installation Department.

REFERENCES

1. 'New Band I Transmitting Aerial for the Wenvoe Television Station', Research Depart.ment Technological Report No. E-~14/ll.

2. Detailed information on the construction and dimensions of the aerial IS

given on the following drawings held by Planning and Installation Department:

Band V Panel Aerial: Marconi drawing 'fBO-2295

Assembly similar to: Marconi drawing EIT02-8240, Sheets 1 and 2

GID

panals 752ft 6in (229·4m) ------r......-I-.-.--r -

736ft 6 in (224, 5m) -~l-----

1 1 1 1 1 1

1 1-----1 1 1 1

2

I __ ~_-1 1 1 1 1

3

I---··--~

1 1 1 1

4

1 ____ -1 1 1 1

5

1 1-----I I 1 1

6

720ft 6in (219·6m) -------,.L---L..-.f-J..J..........I.,

714 ft 7in (217, Bm) ----L.......--\r--+----r-......J

Band 1Z: aarial

Band Y distribution transformars

Band I aarial

Fig.1. Genera I arrangement of aerials on mast

::t-lightning /

conductor

26in (660mm)

+

+

+

glass fibra cylinder, 5ft (1· 52m) diamatar

Fig. 2. Arrangement of aerial panels.

vibration dam~r

laddar

Bin. (203mm) _L_.

L 11·9in .1 i<302mm)I I I

1=

J

=0

1

J

=

Fig. 3. Construction of singla penal.

4·5in (114mm)

H

tiar; 4

5

6

fOGa: A B c D

balanca load

diplaxer "i phasing langth

Fig. 4. Schczmatic of distribution fczczdczr arrangczmcznt

(Iowczr half aczrial)

N

Fig. 5. Horizontal radiation pattern: Chann<21 41 HORIZONTAL POLARIZATION

Vision corriar 631' 25Mc/s, Sound corrilZr 637- 25Mc/s

MlZon IZfflZctivlZ gO'In: 11·1 dB PlZok vision tronsmittlZr powlZr: 2 x 12kW

MlZon E.R.P: 310kW -- -- Stockholm E.R.P. limit

Unit fiald corrlZsponds to an E.RP of 500kW

Fig. 6. Horizontal radiation pattl2rn: Channel 44 HORIZONTAL POLARIZATION

Vision carriar 655·25Mc/s, Sound carriar 661· 25Mc/ s Maan affactiva gain: 11· 2dB

Paak vision transmittar powar: 2 x 12kW Maan E.R.P: 320kW

----- Stockholm E.R.P. limit Unit field corresponds to an E. R.P. of 500kW

Fig. 7. Hori zonta I radiation pattczrn: Channl2l 47 HORI ZON TAL POLARI ZATION

VIsion corri(lr 679·25Mc/s, Sound corri(lr 685·25Mc/s M(lon (lff(lctiv(l gOin~ 11· 4dB

P(lok vision tronsmltt(lr pow(lr: 2 x 12 kW M(lon E.R.P 330kW

----- Stockholm E.R.P. limit Unit fi(lld corr(lsponds to on E.R.P. of 500kW

N

Fig. 8. Hori zontal radiation pattczrn: Channczl 51 HORIZONTAL POLARIZATION

Vision carriczr 711'25Mc/s, Sound carriczr 717·25Mc/s

Mczan czffczctivcz gain: 11· 4 dB Pczak vision transmittczr powczr: 2 x 11kW

Mczan E.R.P.: 300kW

Stoc kholm E.R.P. limi t Unit ficzld corrczsponds to an E.R.P. of 500kW

1·0

0·9

0·8

0·7

;; 0·6 0'1 c !! ... III

~ 0·5 ;;:: et > ... ~ 0·4 '-

0,3

o· 2

o· 1

w '(

r--

0 o

"' - j--------

~

----- ----

---1-----

'\\ " \ \~

1\\ -----

\\ ---- --- -

, \

\ \

~ \\, \\\ \\ r, \\ \ ~ V-~ \1 ..... ~\ ,f! ~ , ~ ,~ -, \~ If) I \ \~ \. r~ ~ 11

" "' 1\ 1-, .......

~ ..... \ '\' I\..... ...-::,' ~ ""'" , \. ~ ~

l-le .... ~ ~ .,.- K ... ~ ~~ ,.....

2 3 4 5 6 7 8 ongl~ b~low horizontal, d~gr~~s

20 10 5 4 3 2·5 opproximota rong~, km

Fig. 9. Vczrtical radiation patt<zrn on bczaring 0° E.T.N.

• Channcrl 41

--- Channel 47

Channel 44

------ Channel 51

- -- Specified minimum field

1·0

0'9

0'6

0·7

t 0·6 c (lI L.

t: !! 0·5 (lI ;;::

0·3

o· 2

o· 1

11' "I

..

o o

"'\ \ ~\

'\ ~ \ \ \ , ,

I~

" \ , \

, L r--~

1 .. .4 '1'-~ K

~ ~ I'. \~ I-"'" // I'\~\ ,~ -, (/

i' .. ~P' \ \\ ~ " \ \ l\) -..... ,..... \ 1\ ,. ~ /)'OC---. '~ ~2 ~ V ~,

." -, 1' ...... ,

V "-V 2 3 4 5 6 7

anglcz bczlow horizontal, dczgrczczs

2\:c~-~1~b-----5~' --47' -----,~!;--~. 5 approximatcz rangcz. km

" ~ "

B

Fig. 10. Vertical radiation pattern on bearing 900 E.T.N.

........ ...--......... Channlll 41 Channlll 44

--- Channll147 ------ Channlll 51

--- Spllcifilld minimum fillld

1· 0 ,--_.. ....... :-0--,--,--- .-.-- ,---" ,'-,-,---- -.- . -----

I#~~ 'iIiIr-+--M~+-_t---f---r-- --- ----f---+-- 1-'" '--'-1"-'- ------t .. - .. -

O' 9 r 1"\ - r-+---' -+--t--- - ----- --.. -j-.... -j---... --

~ --- -1 --- -- ----t----+---- .. --- ----t-.-t~

0·8 __ +---+ __ -\ll\\~_+-___ I-- ---

\\ --- ... -. t-·-------

f---f---- -- -+l+-+---+---f--+-.-+---- ,,-- -- ... - c·-.. --·- ----..... ---

\\ O· 7 t---+-_t_-f--\+t- --+----1---+ .. --+---+---+--.-+--- -I-

--l\ t-c-·---+--+---t-·----+--+--1----+--- --­,

.-- ------

, ~ O' 61--+--+-----f--·-lj1\----+---t--t---t--t--+----+--t-·---r---- .. - "--r'-'---

g' '1\ !! t---+--f---+---It+--+.- t-----+--t--f--+-----jl----r-.--.t----+--t-.-.-j

; \' .~ 0,51__- 1---. t---f----1I-ir~ ... +--t--+-+--I----+--+---+---- , ~ , .~ \ Q , ~ O' 4~---+--_t_·-+--+-_; .. ---- .--.. --- ----.f----t----r--- ------ ---+----i----.

\ It I ,,-1'--.. /--- r--.-+----II----+-~~t___+_ If'" L~ -- - r--i---t---t-.--

~ f~~~" ~ O' 31----I---+--+--+-... ~\ \"'\\-+--+V+-/ ~\.-~ \ ----t-----t----t--t----

r---+-+--+--+~~~\~'I'~,~)·7-~~/~,+~~~~\--r~-_+--r---~\ \~~ / V \ '\' ~

-+---ft~~~--+-_+_-I__-

I' .. \~ L \\, O· 2 t----+-+

,----..... " ,~

°0~~-~-~-~2--L-~3-~-~4-~--~5~--L-~6~~--~7~-L---8

L 20 10

angltz btzloW horizontal, dtzgrtztzs . _______ L_._---1 __________ .L........ ___ .J

5 4 3 2'5 approximattz rangtz, km

Fig.11. Vertical radiation patterns on bearing 1800 E.T.N.

• • Chonntll 41

Chonntll 47

Chonntll 44

Chonn<ll 51

--- Splicifitld minimum fi<lld

1'0

0·9

0'8

0·7

;; 0·6 en c ~ ... III

1J -; 0'5 ;,::

Cl> .~ ... o 'i! 0'4

0'3

0·2

0'1

/ , '.

"" "

~~

x~ \\ \

\ \ \' , \

----,---- ------ -

--~ --- ---

---1---- ----- - ----

-- - ------ ---

----

\ \

\

\l\ ~""" \ ~~ It --1',\

~\~ ~~ . .,/ n ~ \

1'. I~ '. ~ li' ,-' I\~ -'-. \ \ \; ~, -.. ~-~ If I ..

\ \ \

"-~ ~. \ \ , \ ~ .. \ \

1""--" H .. ~ -~ "- 7:

"-, ..

23456 angla balow horizontal. dagraas

.

./ - .... ""- ,-... -~ '--

,., 7

~~I ____ ~I __ LI ___ ~ ___ ~I~ ___ ~ 20 10 5 4 3 2'5 2

approximata ranga. km

~ ...... 8

Fig. 12. Vertical radiat i on patterns on beari ng 2700

E. T. N.

• • Channel I 41 Channell 44

Channczl 47 Channel I 51

--- Spczcifield minimum ficzld

Printed by BBC Research Department, Kingswood Warren, Tadworth, Surrey