Hi Ernie,
There are two differences between USB and LSB that could explain
why the carrier is worse on one mode. The BFO (or carrier oscillator)
changes frequency when you change sidebands. If the carrier balance is
adjusted for the best null at one BFO frequency, it may not be as good a
null at the other frequency. I doubt that difference is very much,
probably only a few dB at most and not tens of dB. The other is the
slopes of the crystal filter skirts are not exactly the same on the high
frequency side and the low frequency side of the filter bandpass. Also
the position of the BFO in relation to the filter skirts is not
identical on both sidebands. The net result of all of those factors
makes the carrier reduction different on opposite sidebands. My guess is
that if you get the instability of the modulator balance fixed, it won't
matter anymore.
DE N6KB
theErnie Popp wrote:
Omni 6+
During CQWW ssb contest, I noticed that I had carrier present on LSB while
operating on 40M. I checked and found it was present on all bands only on lower
side band. Upper seems fine. It seems more severe on 40m. I first checked the
9mhz bfo crystal. It was close and I fine tuned it a little. This had no real
effect and still had carrier on LSB. Next I adjusted the balanced mod. I'm
not sure if their is a special procedure for this. I was able to completely
eliminate the carrier. After several day, the problem reappeared. Once again,
I adjusted the balanced mod to correct the problem. Checking tonight it's
back. I'm assuming that something is unstable in the balanced mod circuit.
Why is USB not affected? Has anyone experienced this? Any Ideas?
Tnx, Ernie K2EP
k2ep@arrl.net
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