[amsat-bb] Re: SINAD Vs. Noise Figure Testing

[Nate Duehr]

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