[Test-Equipment] spectrum analyzer as radio receiver

[gil smith]

Hi folks:

I have been wanting to get a radio receiver to search for some rtty
signals, but not quite knowing what I am looking for, and not wanting to
shell out the money just yet, I have been pondering some budget alternatives.

One such wacky thought was to use a spectrum analyzer as a radio receiver.
So I dug out some manuals and fired up my 141T mainframe, currently
populated with the 8554L 1250MHz RF, and 8552A IF sections.  I just stuck a
little whip antenna on the rf input.  Sure enough, I can find a signal
spectra, set the scan-width to ZERO, and fine tune the signal and see the
time-domain representation on the crt.

So I hung a scope on the vertical-output from the IF section, and saw a
similar (perhaps inverted) signal.  I stuck some amplified headphones on
the vertical-out, and heard some noise.  Tuning around, I found music up
around the FM band!  This brings up my first question:  I expected to just
get AM reception, so what am I hearing just over 100 MHz?  This can't be
demod-ing FM stations, can it?

I found some more broadcast-like programs around 550MHz, found some data
(nicely demodulated) in various spots, and lots of undecipherable stuff
around 900 MHz where phones and things make noise.  Didn't find much below
100MHz, but the antenna is only 6".  

I also have an 8553B 110MHz RF section that I did not yet try, which would
likely benefit from a better antenna choice for lower freqs.  And I have
the companion Track-Gen/Counter -- would this provide a freq readout when
in zero-scan mode with the 8553?  Or, is there a way to use an external RF
signal generator to select carrier freq?

yeah, it's late -- any thoughts appreciated,

gil


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