An update on my ground loop problem on my Pegasus / computer interface:
Based on a suggestion from the group (thanks, K9PH), I grounded my computer
chassis to my station ground. That seems to have cleared up the hum that I
was noticing on TX when monitoring. I was able to make some PSK contacts
and no one mentioned any problems with my signal. However, ocassionally, I
noticed evenly spaced thin vertical lines on the DigiPan display during RX.
I didn't measure too closely, but the were about 120 Hz apart. When I've
seen this before, I've attributed the problem to a ground loop and putting
an isolation transformer in line usually cleared them up (there is an
isolation transformer in line now). The interesting thing is that these
lines would come and go and I couldn't determine a pattern to their presence
or absence. I can come up with 3 suggestions:
1) The ground loop is still there, but attenuated, so that when I receive a
decent strength signal it masks the effect
2) The vertical lines are actually caused by an artifact of the DSP
filtering when a strong signal is just outside the filtering passband.
3) There is actualy a 60 Hz component getting into my received signal due to
some faulty power transmission equipment (I make this suggestion because
there is something like an arcing insulator that randomly gives me S7+ noise
levels - though it was pretty quiet last night).
73,
Mark
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