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Measurement of CNR..need reviews and help

Question asked by ankur_reseacher on Jul 15, 2009
Dear Readers
I have made a setup to measure CNR for a cable TV setup. Initally I used a spetrum analyzer . Later I decided to work with ESA series. I am still looking for some advise / help on the test setup that I designed and some issues that were present in the setup.

Transmitter ---> my channel under test --->RF coax (75ohm) ---> to spectrum analyzer.

The bandwidth of PAL-B (indian TV) is 7Mhz. I measured the highest peak of the visual carrier (roughly 25 dBmV) in channel BW. this was the value of carrier I was looking for (ignoring the other sigmals of chroma and sound). Now hard task is to measure noise present in the signal ???
I switched off the transmitter and measured the random signals (noise) in the band (the band of visual carrier just measured) .. the noise was pretty fluctuating . i didn't go into the jargon of noise measurement rather just took the most common value .. it was about  (-25) dBmV.
this gives me a CNR of roughly 50.

But there are some issues in this working .
I assumed the internal nosies of the transmitter are negligible. however, the internal noises like thermal noise , shot noise , flicker noise are totally unknown to me. is my assumption correct? is there some way to measure the noise of the transmitter while we have the signal on . (in my case transmitter isa CD player,which is a single channel transmitter ).