04/13/23
UNIVERSAL ENGINEERING COLLEGE, THRISSUR- 680123 Department of ECE
EC09 L05: Satellite Communication
System noise temperature @
Satellite Link Design
System noise temperature @
Satellite Link Design
AJAL.A.J Assistant Professor
Mob: 8907305642 MAIL: [email protected]
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 }
Noise temperature Noise temperature
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
Noise temperature Noise temperature
Condition 1
If A/R produce no noise :Noise Tθ = 0 K
Condition 1
If A/R produce no noise :Noise Tθ = 0 K
Noise temperature Noise temperature
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.
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 Ratio :G / T Ratio :
Noise figure is used to specify noise generated within a device.
Noise figure is used to specify noise generated within a device.
G / T
G / T
KTS BN
PT GT GR C/N =
λ
4 πR
2
G / T Ratio :G / T Ratio :
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