[Test-Equipment] spectrum analyzer as radio receiver

[gil smith]

Thanks to all who replied on this.  Some of you mentioned a few items:

- freq range:  Yeah, I was using a 1250 MHz RF plugin, but I also have
another plugin that can be set for 1 KHz to 110 MHz, or 1 KHz to 11 MHz.
Low-freq operation should not a problem for the rtty area of interest.  The
IF output from the RF section to the IF section is at 50 MHz.

- sensitivity:  well, it's not really spec'd this way, but it says average
noise level <-100dBm @ 10 KHz IF BW, spurious responses and IM products are
 <70 dB below signal level @ -40dBm input level, and residual responses are
< -110dBm.

- stability:  Sheesh, this thing will zoom in on a signal and not move, and
has a freq-stabilizer as well.  With stabilization, the signal is
phase-locked within 10 KHz.  It says noise sidebands are > 70 dB below CW
signal when > 50 KHz away from CW signal, with an IF bandwidth of 1 KHz.

- bandwidth:  I can select an IF bandwidth from 10 Hz to 300 KHz.  Is that ok?

- the FM stations I heard:  "slope detection" was the popular response.

- But for rtty use, I guess I need ssb demod.  So perhaps this is in vain.

gil


At 12:19 AM 3/25/03 -0700, you wrote:
>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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;  vaux electronics, inc.             480-354-5556   
;  http://www.vauxelectronics.com     (fax: 480-354-5558)
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