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Improved AO-40 TLM with the DSP-2232 and FT-847



Hi,

I did a little poking around with the analog part of the DSP-2232, and was
able to make some slight but noticeable improvement in the G3RUH telemetry
data recovery.  What I found seems to be consistent with bits and pieces of
information I have heard over the years.

Lacking access to the DSP chip digital output, which of course is what I
really need to do it right, I looked at the analog data out of the NE572
compandoring chip, U28, which feeds the DSP chip.  Using a dual channel
scope, I compared the raw audio from my FT-847 data port, which is a
constant level source, and the output of the chip at TP1 for radio port 1,
and TP2 for radio port 2.  I ended up backing off the AGC pot to about the
10 or 10:30 position, which resulted in the maximum signal output from U28
without any compression of the signal.  The default 12 o'clock position
isn't bad, but definitely brings up the noise unnecessarily.  Looking at a
couple of passes shows a 10-15% improvement in recovery.  That is better
than it sounds, since it comes from the marginal squint angles.

As the default position is 12 o'clock, it would be easy to back off (or
advance) the AGC pot for best recovery, but reset it to the factory default.
It seems to be very uncritical.  I suspect that the type of AGC response in
the rig may also be a big factor here.


Alan
WA4SCA

-----------------------------------

To get the attention of a large animal,
be it an elephant or a country, it
helps to know what part of it feels
pain. Be very, very sure, though, that
you want its full attention!

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