TS = System noise temperatureTS = System noise temperature

• Boltzmann constant = 1.39 x 10 -23 J/K

• Boltzmann constant = - 228.6 dB W/K/Hz

Thinks to be noted

Noise temperature Noise temperature

Usually achieved without physical cooling .

{ 30 k – 200 k }

Usually achieved without physical cooling .

{ 30 k – 200 k }


Using Ga As FET ,

{ 30 k – 4 GHz 100 k – 11 GHz 150 k – 20 GHz }

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 !

How an A/R can have a Noise Tθ lower than physical Tθ !

From a matched load at the same physical Tθ placed at the i/p to the A/R

From a matched load at the same physical Tθ placed at the i/p to the A/R

Noise produced by an A/R

Thermal noise

Noise Tθ simply relatesNoise Tθ simply relates


Condition 1

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

Condition 1

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


Condition 2

If A/R produce less noise than a matched load @ same physical Tθ :

Noise Tθ < physical Tθ

Condition 2

If A/R produce less noise than a matched load @ same physical Tθ :

Noise Tθ < physical Tθ

Total thermal Noise power 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

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 Ts we do this by determining Ts

Ts = S/M Noise temperature Ts = S/M Noise temperature

NOISELESS RX

NOISE SOURCE

Tθ

TsTs

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

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 :IT USUALLY INCLUDES NOISE FROM ANTENNA NOTE :IT USUALLY INCLUDES NOISE FROM ANTENNA

RF A/R IN SATELLITE RX KNOWN AS LNA WHY?

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

RF A/R in a satellite communication Rx generate a little noise as possible .

so it is called a LNA

LNBLNB

LO IF A/RLNA

ARE ALL INCLUDED IN A SINGLE PACKAGE CALLED LNB

LNB IS LOCATED IMMEDIATELY BEHIND THE ANTENNA FEED

Noise figure & Noise temperature

Noise figure & Noise temperature

Noise figure ( NF )Noise figure ( NF )

Noise figure is used to specify noise generated within a device.


NF ____________

NF ____________

(S/N) O/P

(S/N) I/P NF =

CONVERSION CONVERSION

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

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

NOISE Tθ

NF

CONVERSION CONVERSION

T = T0 ( NF -1 ) T = T0 ( NF -1 )

T0 = referenceTθ = 290 K

T0 = referenceTθ = 290 K

NOTE :NF is frequently given in dB & must be converted to a ratio before being used

NOTE :NF is frequently given in dB & must be converted to a ratio before being used

G / T Ratio :G / T Ratio :




G / T

G / T

KTS BN

PT GT GR C/N =

λ

4 πR

2


G / T

G / T

KTS BN

PT GT GR C/N =

λ

4 πR

2

K BN

PT GT C/N =

λ

4 πR

2 G

TS

INFERENCE INFERENCE

NOTE :satellite terminals usually have - ve G / T ie: the value is below 0 dB / K

NOTE :satellite terminals usually have - ve G / T ie: the value is below 0 dB / K

C/N α TS

G

System noise temperature @ Satellite Link Design

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