Originally, two way shops set FM rigs up for 20 dB quieting, on a volt
meter (crank up the signal until the AUDIO VOLTAGE, UNMODULATED, was
1/10th the voltage of a no signal audio output . Tho, for the most
part, this works well, there are constraints on sensitivity, because of
bandwidth concerns, and , as bandwidth is halved, the signal improvement
is 6 dB (quadrupled). Sinad is Signal/Noise /signal/(noise+distortion)
and in fact, in recent times , devices that will measure it are built
into many pieces of test equipment (IFR meters comes to mind), also
look for an outfit called "SINADDER" . The main thing is that it adds
a "Bandwidth" component to the sensitivity equasion. It is measured
with a 1 KHz tone, at (in FM), 3 KHz deviation- and the smaller the
signal that is detectable , with this constraint, the more sensitive
the reciever is considered to be! This also works at SSB/AM. Tho, it
is true that this measures Sensitivity, it includes a BANDWIDTH
component, that a (noise figure/ quieting) would NOT consider (at least
fully!) Hopefully, this is helpful-- Jim NN7K


For SSB and CW, on the other hand, the noise is purely additive so all
you need to know is the receiver noise figure. Once you know that
(assuming that it's not a really strange radio) you know everything
about it's performance. Given the noise figure in dB you can easily
calculate the 12dB SINAD should you be so inclined, as well as any other
signal vs. noise figure you should want. You have a good reason to
believe that the noise is white so you can even take an SSB receiver and
calculate the noise figure of the thing after you tack on an audio
bandpass filter for CW. This is _not_ the kind of thing you could do
with FM.