Hello Shakeel, there is no absolute answer to your question as "noise" and "signal" are not defined by physics but only relate to your purpose... Take an example: you want to excerpt specifically the sound of the second violin of the New Year Vienna Concert, because you aim at characterizing this instrument from Stradivarius, and the whole orchestra becomes noise ! But if you aim at recording the symphony, it becomes your signal and noise turns to be simply the coughing and sneezing lady of the third row...

If you can switch your "signal" on and off without altering any other element of the "noise", it turns easy, but this is NOT the common case because the system generating the signal also contribute to the noise: meaning you have to scratch your head to assess what is really your "signal" and your "noise" before undertaking any measurement, operate your spectrum analyser etc. Hoping this helps!

Hello Bernard this is very different reply. I am looking the answer what is defined in wireless communication theory. In theory if r denotes received signal then r=hx+n. h is channel, x is the transmitted signal and n is awgn noise. But in spectrum analyzer we see average signal or What I don't know. How to differentiate noise and signal in spectrum analyzer. Can anyone explain through pictures of the spectrum analyzer screen. How we can calculate signal to noise from spectrum analyzer screen.

I insist: you have to define first of all what is your "signal"! Your spectrum analyser cannot decide on its own what is "signal" and "noise"... (of course the theory can)

Hello Mr Shakeel

I think a suitable way to measure SNR is by calculating S+N/N using spectrum analyzer.

First with the fundemental signal OFF, measure the noise signal integrated over your channel bandwidth. You can use the channel power function of the spectrum analyzer.

Then you turn ON your signal of interest and then measure again the signal power integrated in your channel bandwidth using the same procedure as before. This will be Signal plus Noise.

After that the ratio can be taken of the both.

Any suitable RBW can be used for this procedure as the signal and noise power is being integrated over the channel bandwidth.

Alternatively, if the RBW is kept equal to channel bandwidth, the above mentioned procedure can be repeated without using the channel power function of spectrum analyser.

Hope that helps