Well, in the end, it turned out to be the IOTA power converter.
This is something that didn't show up in extensive testing here, and
didn't show up at the site for a while either.
With modern SMPS designs, you can't really use the term "switching
frequency", since the controllers do things like pulse skipping
under light load, or frequency modulation to "spread" the noise
making part 15 easier. Even an older switcher that runs at a fixed
frequency, will be doing PWM, so there will be another frequency
component that moves around under load.
However that works out in the IOTA, it was apparent that this was
the source. I was able to hear broad hash on my IC-R3 held close to
the unit, and tuning up to the repeater input, I could hear the mix
product as well. I replaced it with a linear supply since I had one
handy, and the problem's been totally gone for over a week.
:)
I spoke to IOTAs technical people, who were pretty knowlegable.
They offered to exchange the unit, and came up with the same
probable fix that I did, ferrites on the line cord and DC cables.
Since the unit is in a metal box, I think that this will likely
solve the problem.
Key symptoms of this problem:
Comes and goes.
Gets through CTCSS squelch, IF you encode the same tone you decode.
(because it's mixing your output back in)
Has audio that sounds like an echo or fast repeat, but the audio is
rather weak.
Cause: Repeater output mixing with switching power supply noise,
producing a real carrier on the repeater input.
Won't happen on a 440 machine, or probably a 220 machine, due to the
wider splits. Switchers are increasing their operating frequencies
to keep the magnetics small, so having significant noise at 1.2 MHz
bothering a 220 machine isn't out of the realm of possibility.
Yahoo! Groups Links
<*> To visit your group on the web, go to:
http://groups.yahoo.com/group/Repeater-Builder/
<*> To unsubscribe from this group, send an email to:
[EMAIL PROTECTED]
<*> Your use of Yahoo! Groups is subject to:
http://docs.yahoo.com/info/terms/
