Duane,
I followed your instructions, downloaded the Spectran software and was able to
set the IF gain control with no problem. It was easy to find the "knee" in the
gain setting. The Spectran software is very entertaining. Fun to play with
various filter settings and watch the results. Thanks again for the help.
73,
Dan KF9BP
-- Duane Grotophorst <n9dg@yahoo.com> wrote:
The IF gain pot is easy to spot and is labeled "IF
gain". But I forget which side of the radio it is on,
it is easy to spot once the cover is removed though.
To really be able to set it correctly/accurately you
will want to get a copy of the freeware Windows
program called Spectran from:
http://www.weaksignals.com/
It is not a very big program and uses a standard sound
card. The 3.5mm cable supplied with the Pegasus is all
you should need to hook it up to the line in of the
computer. Or if you already have sound card interface
for PSK31 etc. modes that will work just fine as is.
Some of the other weak signal audio analysis programs
out there would probably work fine too. However the
typical PSK31 program however doesn't always let you
see the low level spur.
Since you already have a unmodified (presumably)
Pegasus you can look at the spectrum output from it
with no antenna attached. Chances are you will see a
very weak but steady spur somewhere in the audio
passband (most people can't even hear it, and with an
antenna attached it is buried in the band noise). That
can be your guide for determining the proper (factory)
level of the IF gain. Critically important though is
that you to do this adjustment with no antenna
attached, even better is with a 50 ohm load on the
antenna input.
>From what I can tell with the unmodified Pegs that I
bought the factory setting appears to be at the point
where the spur "just" reappears after slowly backing
off of the gain pot from max. That point is also very
close to a very pronounced "knee" in the response
curve of the IF gain pot as you adjust it, that is why
it is very difficult to get it back to the original
factory setting by simply using a reference mark drawn
on the pot alone.
When the IF gain pot is advanced ever so slightly
beyond the factory setting point the spur does
disappear. And when the IF gain pot is turned fully
clockwise you also will see a real significant rise in
the background noise of the the audio output and the
spur will be buried. In my experimentation with the IF
gain pot settings the degradation of strong signal
handling performance begins as soon as the spur is
gone.
And once you have the sound card setup and running
Spectran you may want to play around some more with
various settings of the IF gain pot for the fun of it.
And then look for some strong signals and see for
yourself what it really does.
Duane
N9DG
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