Michael Heim wrote:
Stan makes a good point here, especially for FM sensitivity. I worked in the 2-way business for a long time, and typically a sinad measurement would be something like the value of microvolts at the antenna input for 20 dB of quieting of the receiver. It is basically a measurement of FM receiver sensitivity. It will also show mis-aligned IF strips and detector, but for the sake of arguement in this case, lets say the receiver is functioning normally. The goal should be the minimum amount of signal input at the antenna connector quiets the receiver 20 dB.
http://www.repeater-builder.com/tech-info/20dbquieting.html
Often times folks building repeaters and/or doing other weak-signal (contesting) work at VHF and above have great documentation and information that applies just as much to satellite operation.
It's always worth "popping our heads up" from our own little RF worlds and looking around a bit once in a while. (Like Prairie Dogs.)
I agree with you, a SINAD measurement on an SSB receiver is kinda not the right idea. It'll show you something, but what... I'm not quite sure. It CAN be used for a comparison measurement for changes, though.
Thus, the best thing about learning how to make a SINAD measurement, measuring or at least calculating Noise Figure, or WHATEVER measurements is this:
You can make CHANGES and see if you made things better or worse.
Why is that important?
It changes your hobby from subjective ("that sounds better") to quantitative ("I made my home VHF setup 3dB more sensitive on VHF today"), which is a sign you're trying harder than the majority to have a great receiver setup and antenna system.
Another useful measurement is to find the receiver's sensitivity while injecting the test signal while connected to an outside antenna, after doing it without... to see how local noise/intermod/etc., affects your receiver.
A home-made "Iso-Tee" set up for a known amount of loss on your test setup, or a directional coupler with a known amount of loss are needed for that test.
Nate WY0X