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Re: Further AIDC 3733 adventures



I did a similar test today and confirm your results. Before starting, I
removed the 2.4GHz. stub. This got rid of the hole in my frequency response.
I set up the 3733 with an ancient old HP8616A connected to the input using
an N connector. I connected the output to an HP8593E spectrum analyzer. I
set the spectrum analyzer to zero span and turned on the FM demod. I reduced
the output of the generator until the signal got noisy and proceeded to
tweak the filter adjust screws for best quieting. My input level at that
point was about -104 dBm. The adjustments were extremely broad. After
setting the filters, I checked the frequency response by manually sweeping
the signal generator. The response was now very flat across the 2.1 GHz. to
2.5 GHz. band.  I'm thinking about trying to replace the first filter with
one of the Mavin filters with a much smaller BW. The only problem is that
they were pretty lossy to put in front of the LNA.

Howie, AB2S

----- Original Message -----
From: "Art Goldman" <aegoldm@lts.ncsc.mil>
To: "amsat-bb" <amsat-bb@AMSAT.Org>
Sent: Thursday, April 05, 2001 4:27 PM
Subject: [amsat-bb] Further AIDC 3733 adventures


> Finally had the chance to hook the 3733 to the test
> equipment, and attempt to tweak the
> comb/digital/interdigital filters...
>
> Device: AIDC 3733, unmodified
> N Adapter in place of dipole antenna
>
> Input: Agilent signal generator, at 2401.0 Ghz, -100dBm
> Output: Agilent Spectrum Analyzer, set to center on the
> spike at 123.0243 Mhz
>
> I tried turning each of the hex adjustment screws on both
> filters but saw no appreciable effect on the scope. My
> filters only had screws in two of the three holes. I moved
> the center screw to the edge on each filter and tried there
> -- no effect.
>
> I'd have to conclude the filters are indeed broadly tuned.
> We need to look elsewhere for solutions.
>
> I found one interesting phenomenon. When I touched my finger
> on the large screw immediately below the top filter, the
> gain went up over 10dB. Now if we can figure out how to
> reproduce the effect with a capacitor. Perhaps when cloning
> becomes all the rage there will be enough fingers to go
> around, but until then.......
>
> As for the crystal. It is indeed temperature sensitive. At
> rest, I measured the output frequency at 123.0243. When I
> put my finger on the crystal and heated it up to body
> temperature, the output frequency went up to 123.0268 -- a
> swing of 2.5 Khz. Take the finger off and the peak slowly
> retreats to 123.0243.
>
> That's it until we get our (slightly incorrect) new crystals
> next week.
>
> 73,
> Art, N3OY
>
>
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