LNA Gain vs SNR: Can Increasing Gain Reduce Sat Tx Pwr?

[mp3car]

If you have a satellite that is transmitting at X dbm to a ground station, will increasing the gain of your LNA allow the satellite to use less transmit power? It seems like you'd have to improve the SNR in order to increase BER or Eb/No... If you just increase gain of the LNA, then yes, your signal out of the LNA would be stronger, but so would the noise, which would give the same bit error rate as the lower LNA gain... Is my thinking correct? It seems in order to decrease required transmit power of the satellite and have the same BER at the ground receiver, you would have to do something to improve the SNR... and you can't really do anything to reduce atmospheric/solar noise, right? You could make a "cleaner" first stage in the LNA i suppose, but "just" increasing the gain of the LNA as a whole seems like it wouldn't really allow you to lower satellite transmit power...

 

[Jeff Rosenbury]

You are correct. Increasing the gain on your LNB will not reduce your SNR. There are some tricks you can do to reduce noise, but most of them are used already.

You can limit your frequency band. Since the noise distributes over the band, limiting the band cuts noise. Of course you need the band to get the signal. But extra, unused bandwidth should be limited. So don't go with a wideband amp. One might even use some clever manipulation of the band to lower noise.

You can use either forward or backward error correction, but that cuts into bit rate.

Antenna directivity on both the transmit and receive side increases the signal without increasing the noise.

Some noise is not random, so it can be filtered.

Reducing noise is important and valuable.