# How do you take into account the SNR of a transmitter in a fade margin?

I have a fade margin for a RF bridge, but it only compares the sensitivity of the receiver to the received power - or alternatively calculates the Eb/N0 from the net received power divided by the thermal system noise. Intuitively I think I should subtract some dB from the power budget due to the transmitter's SNR, but removing 30dB SNR from the net power received kills everything so I find it hard to believe this is the right way.

Care to explain?

The first thought I had was to get the noise power from the radiated power and the SNR, then multiply this noise power by all gains of the chain, and at the receiver end convert both the resulting noise and the previously calculated received power (for infinite SNR at the transmitter's output) into µV into a 50Ohm load - then subtract the µV. Does that make sense?

• do you mean the receiver's noise factor? Receivers don't have an SNR as an intrinsic property: the SNR is the ratio of the signal power to all the noise power, with both signal and noise power being determined by many variables such as the receiver, the antenna, the feedline, the path, and the transmitter. Commented Aug 11, 2021 at 18:59
• Thanks for the reply, Phil Frost. Glad to see you here as well. I have updated my post to make it clearer, you're absolutely right. Commented Aug 11, 2021 at 19:11
• I'm still not following. What is "the transmitter's SNR"? Commented Aug 11, 2021 at 20:53
• It just says in the transmitter's datasheet "SNR=30dB" (and it's not a receiver at the same time). I would expect it's just the SNR of the radiated power, since the transmitter must amplify its own noise at the same time as the input signal? Commented Aug 11, 2021 at 20:57
• I guess it could be that? 30 dB isn't very good if that's true. Commented Aug 11, 2021 at 21:50