Antenna Gain vs. Amplifer Gain

[steppermotor]

If the SNR at a receiver output is say 12 db, and the antenna gain is increased from 3 db to 6db, but the antenna temperature remains the same, calculate the new SNR?

I think the SNR wouldn't change because antenna gain is not the same as amplifier gain and the noise figure did not change since the antenna temperature remained the same, but I'm not sure.

 

[dot4]

Actually, it would. You are right that antenna gain and amplifier gain are not the same. Antenna doesn't add any power to signal like the amplifier do, but in this case (reception antenna) antenna is able to receive twice as much power than it did before, while the intensity of EM field at reception point remained unchanged - it receives from one direction more than from another. And that is the reason why we use dBi, as a unit for this type of gain, simply meaning dB over Isotropic radiator.
So your noise parameters stayed unchanged and you have 3 dB stronger signal behind the antenna.

 

[steppermotor]

Actually, it would. You are right that antenna gain and amplifier gain are not the same. Antenna doesn't add any power to signal like the amplifier do, but in this case (reception antenna) antenna is able to receive twice as much power than it did before, while the intensity of EM field at reception point remained unchanged - it receives from one direction more than from another. And that is the reason why we use dBi, as a unit for this type of gain, simply meaning dB over Isotropic radiator.
So your noise parameters stayed unchanged and you have 3 dB stronger signal behind the antenna.

I see so if the receiver output SNR before was 12 db, now it would be 15 db right, since the 3 db gain, but the noise figure remains the same, because SNR input signal increases? Since SNRout=SNRin(db)-NF(db)