# System noise temperature @ Satellite Link Design

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Published on March 7, 2014

Author: ajal4u

Source: slideshare.net

## Description

How an A/R can have a Noise Tθ lower than physical Tθ !
RF A/R IN SATELLITE RX KNOWN AS LNA WHY?

UNIVERSAL ENGINEERING COLLEGE, THRISSUR- 680123 Department of ECE EC09 L05: Satellite Communication System noise temperature @ Satellite Link Design AJAL.A.J 03/07/14 Assistant Professor Mob: 8907305642 MAIL: ec2reach@gmail.com

TS = System noise temperature Thinks to be noted • Boltzmann constant = 1.39 x 10 -23 J/K • Boltzmann constant = - 228.6 dB W/K/Hz

Noise temperature Usually achieved without physical cooling . { 30 k – 200 k }

Noise temperature Using Ga As FET , { 30 k – 4 GHz 100 k – 11 GHz 150 k – 20 GHz }

NOISE POWER Where , Tθ = temperature BW = band width

How an A/R can have a Noise Tθ lower than physical Tθ ! Noise Tθ simply relates Noise Tθ simply relates Noise produced by an A/R Thermal noise From a matched load at the same physical Tθ placed at the i/p to the A/R

Noise temperature Condition 1 If A/R produce no noise : Noise Tθ = 0 K

Noise temperature Condition 2 If A/R produce less noise than a matched load @ same physical Tθ : Noise Tθ < physical Tθ

Total thermal Noise power To determine the performance of a receiving S/M ,we need to be able to find Total thermal Noise power against which  signal must be demodulated we do this by determining Tss we do this by determining T

Ts = S/M Noise temperature NOISE SOURCE Tθ NOISELESS RX

Ts Ts = NOISE Tθ OF A NOISE SOURCE , LOCATED AT THE I/P OF NOISELESS RX WHICH GIVES THE SAME NOISE POWER AS THE ORIGINAL RX NOTE :: NOTE IT USUALLY INCLUDES NOISE FROM ANTENNA IT USUALLY INCLUDES NOISE FROM ANTENNA

RF A/R IN SATELLITE RX KNOWN AS LNA WHY? RF A/R in a satellite communication Rx generate a little noise as possible . so it is called a LNA

LNB LNA LO IF A/R ARE ALL INCLUDED IN A SINGLE PACKAGE CALLED LNB  LNB IS LOCATED IMMEDIATELY BEHIND THE ANTENNA FEED

Noise figure & Noise temperature

Noise figure ( NF ) Noise figure is used to specify noise generated within a device. NF NF (S/N) I/P ____________ NF = ____________ (S/N) O/P

CONVERSION NOISE Tθ NF Since noise Tθ is more useful in satellite communication s/m , it is best to convert .

CONVERSION T = T0 ( NF -1 ) T00= referenceTθ = 290 K T = referenceTθ = 290 K NOTE : : NOTE NF is frequently given in dB & must be converted to aaratio before being used NF is frequently given in dB & must be converted to ratio before being used

G / T Ratio :

G / T Ratio : Noise figure is used to specify noise generated within a device. G/T G/T P G G T T R C/N = KTS BN λ 4 πR 2

G / T Ratio : G/T G/T PT GT GR C/N = 4 πR KTS BN C/N = 2 λ PT GT λ K BN 4 πR 2 G TS

INFERENCE C/N α G TS NOTE : : NOTE satellite terminals usually have --ve G //TT satellite terminals usually have ve G ie: the value is below 00dB //K ie: the value is below dB K

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