Radio Basics 2 - pudn.comread.pudn.com/downloads132/doc/563505/2RadioBasics.pdf · Radiocommunications Systems Radio BasicsRadio Basics S/N versus (S+N/N) S/N versus (S+N)/N Given:

Radio BasicsRadio BasicsRadio BasicsRadiocommunications Systems

Topics:

Intermodulation

•Intercept point•Intermodulation products •Intermodulation ratio

Sensitivity

•noise figure•noise bandwidth•S/N versus (S+N/N) and SINAD

RF Power at:

•CW (Contineuos wave)•AM (A3E)•FM (F3E)•PEP (Peak Envelope Power)

Selectivity

•adjacent channel rejection

VSWR

•voltage standing wave ratio (VSWR) •reflection coefficient•return loss / mismatch loss

Radio Basics


Intermodulation Products

Output of a non linear component


L

ff2-f1 f1 f2 f2+f1 2f1+f2 2f1-f2 2f2-f1 2f2+f1

aIM2 aIM3

intermodulation ratio aIM = L(f1,f2) - LIM

Internally generated intermodulation products:Example:

f1, original frequ. 7030 kHzf2, original frequ. 7060 kHzfim2 f2 + f1 14360 kHzfim2 f2 – f1 30 kHzfim3 2f1 - f2 7000 kHzfim3 2f2 - f1 7090 kHz

Can not be removed by filtering

Intermodulation Products


Loutp.

IC2

IC3

Linput

Lf1,f2

Lf1f2

L2f1 f2

L2f2 f1

aIM2 = IC2 -Loutp.aIM3 = 2 (IC3 - Loutp.)

Example:

Amplifier , gain: vp = 100, IC3 = +35dBm, output Intercept Point>> g = 10*lg vp = 20dBInput signal Linp. = -5dBm>> Loutp. = -5dBm + 20db = 15dB wanted: intermodulation ratio:

aIM3 = 2(35dBm - 15dBm) = 40dB

Intercept Point


EK 895Intermodulation (1.5 to 30 MHz; F 30 kHz;)IP3 30 dBm (typ. 35 dBm, related to RX Input)

3rd order intermod by two signals 10 mV (EMV)on the a.m. HF-frequencies?3rd order intercept point 30 dBmInterfering signal -33 dBmDistance from IP3 30-(-33) = 63 dBDistance of IM from interfering signal 2*63 = 126 dBLevel of IM-product -33 dBm - 126 dB = -159 dBm

-159 dBm (= 2.5 nV) is far beyond the reception threshold (0,5uV)

Example Intercept Point and IM Level


Example Intercept Point and IM Level

Law: aIM3= 2x(IC3 - Lint)

Level Diagram for the above Example:

L

IC3 (30dBm)

0dBm

Lint (-33dBm)

LIM3 (-159dBm)

IC3 - Lint

aIM3= 2x(IC3 - Lint)


Sensitivity, Noise

PN = k • T • B • F [W]

k.. Boltzmann constantT.. Temperature [K]B.. Bandwidth [Hz or 1/s]F.. Noise factor

kwsxk 231038,1

Rin = 50 Ω

ReceiverF?

Ueff

∆f

Afout (PN)RFin

(BR)

• Cosmic noise• Atmospheric noise• Man made noise• Electric noise (thermal noise)


Example, Datasheet:

sensitivity 0,22uV @ S/N=10dB, BW=2,4kHzNoise Figure?

1. Step, Signal Power:

3.Step, Noise Figure:

Noise Bandwidth:

in practice this can be considered as the 3dB bandwidth of the receiver, and you get:

BR= 10*log 2400Hz = 33,8dB

Now , the noise adds up to :

-174dBm + 33,8dB + F (RX noise figure) -130dBm

>> F = (-130 – 33,8 + 174) dB = 10,2dB

0

*)(1 dffvpvPo

BR

Sensitivity, Noise

dBmWxxPs 1201068,950

)1022,0( 1626

2.Step, Noise Power:

must be 10dB below Ps (10dB S/N)

-120dBm -10dB = -130dBm

Noise power density:

PRf = k*T [W/Hz], k..Bolzman constant, T.. absolute temp.(oKelvin)

PRf = -174dBm/Hz at a temperature of 25oC

PN = k • T • B • F [W]


Sensitivity, Noise Figure - Matrix

With: kTo + BR + F PS - S/N , a table can be set up:

BandwidthBW 3,1 kHz 2,4kHz 2,1kHz 500Hz 100HzNoise-BW 34,9dB 33,8dB 33,2dB 27dB 20dBNoise Figure Sensitivity (V@ 10dB S/N)7dB 0,18 0,15 0,14 0,00071 0,000310dB 0,25 0,22 0,2 0,0001 0,000513dB 0,35 0,31 0,29 0,14 0,000620dB 0,78 0,69 0,64 0,31 0,14

note: the first column (noise figure) fully specifies a receiver


S/N versus (S+N/N)

S/N versus (S+N)/N

Given: Equipment with S/N = 10dBWanted : (S+N)/N for this equipment

S/N = 10dB means 10 log (PS/PN) = 10

log (PS/PN) = 1; (PS/PN) = 101 = 10

(S+N)/N means: (PS+PN)/ PN = (PS/PN) +1 = 10+1=11

10log 11 = 10,41dBThis means : difference between S/N and (S+N)/N

= 0,41dB@10dB SINAD versus (S+N)/N

For small bandwidths:

S/N (S+N)/N


S/N versus SINAD

(S+N)/N = 40dB

SINAD = D 20dB

Distortion > Noise

(S+N)/N SINAD

0

10

20

30

40

A/dB

f300 1k 2k 3k 3k4

signal

distortion

1kHz rejection filter

noise

10% Distorsion D 20dB

(S+N)/N=10dB

Distortion submerges

(S+N)/N = SINAD

f300 1k 2k 3k 3k4

signal

distortion

1kHz rejection filter

A/dB

0

10

20noise

SINAD ... Signal to Noise and Distortion

(filtered out)

(filtered out)


RF Power CW and FM , AM

CW, FM :

• no difference between modulated and un- modulated powerflat signal envelope:

AM:

variation of carrier voltage and hence carrier power:

URF

URF + UNF =m = 1URF max = 2xURFPmax = 4xPPav = 1,5xP

RF

AF

UUm

URF

URF

PCW=PFM= Pc

Modulation Factor

m=1 means PRF=PAF , 100% mod.

max. CW/FM Power can be specified as 150% of max. AM Power


RF Power SSB , PEP

SSBPeak of Envelope

Single Tone-CW Two Tone - PEP

t t

A/dB

0

-6-36

f

A/dB

0

-6-36

fSingle tone - CW Two tone - PEP

• PEP (peak envelope power) appears if modulation with two or more frequencies takes place • if mod frequencies are in phase, they can cause intermodulation distortion

that’s why PEP must be specified togetherwith linearity (IM-products)Example: XK2900 1kW PEP @ IM 36dB belowPEP


Selectivity

specification in data sheet:M3TR:

• FTZ: occupied bandwidth, 99% of powerwithin 25kHz (Transmitter)• adjacent channel power: -70dBc at fo 25kHz (Receiver)

Typical IF selection (crystal filter, EU230A) Typical IF selection (DSP, EK895)


VSWR

where: • Vmax = maximum voltage on the standing wave• Vmin = minimum voltage on the standing wave• Vi = incident voltage wave amplitude• Vr = reflected voltage wave amplitude

VrViVrVi

VVVSWR

minmax

Reflection Coefficient:11

VSWRVSWR

EiErturnLoss log10Re

if a load has a Return Loss of 10 dB, then 1/10 of the incident power is reflected.

This is a measure of how much the transmitted power is attenuated due to reflection.

Mismatch Loss = -10 log ( 1 -p )2

The higher the return loss, theless power is actually lost.


VSWR II

Influence of line attenuationto the measured VSWR.VSWR is reduced by RF cableloss.

VSWR always should be measured at the antenna connector(not at the transceiver output)


Annex, Noise Bandwidth

Definition of the Noise Bandwidth:

0

*)(1 dffvpvPo

BR

A real world bandpass filter is according toVp(f). BR is defined as frequency widthof the aquivalent rectangle of height vpo

vpo

f

fo

BR

Vp(f)

vpo

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Radio Basics 2 - pudn.comread.pudn.com/downloads132/doc/563505/2RadioBasics.pdf · Radiocommunications Systems Radio BasicsRadio Basics S/N versus (S+N/N) S/N versus (S+N)/N Given: