Yes, the 30-meter metering problem is caused by a ground loop, which
affects the metering circuit on the Omni Six's AF/IF circuit board. The
ground loop affects all metering positions, not just SWR.
And yes, the R.F gain control WILL affect the SWR and other metering
positions, due to the interaction between the 9 MHz IF amp and the
ground loop.
There's a two-step cure:
1) There is a single point on the Omni's lower rear panel that should be
tightly bolted to the chassis. There is a "sweet spot" for this
location that is slightly off-center from the middle of the panel. To
determine the exact location, run the 30-meter frequency as low as you
can. I believe it stops at 9.970 MHz. Running 100W into a dummy load,
take a small blade screwdriver and run it between the gap that exists
between the bottom panel and the chassis while monitoring the speech
processor metering position (The processor shares the same circuitry
that is affected by the ground loop). Note the position of the
screwdriver where the meter deflection in minimized. This is the point
where you neet to attach the back panel to the main chassis with a small
#6 machine screw.
2) If step #1 does not completely eliminate the problem, conduct the
following procedure: the twisted red/orange powering cable on the AF/IF
board should be cut from the wire ties that hold it against the side
chassis. While monitoring the speech processor, route the twisted-pair
cabling in a manner that minimizes the meter deflection.
I have tried bypassing components and a host of other methods, and these
two steps completely eliminate the problem. Also, Ten-Tec advocates
these steps as a fix.
-Paul, W9AC
> > As for the Omni 6's weird 30 meter problems....I've had two of them
> > and they both gave bogus final current readings on 30 meters showing
> > way too much current as compared to the power supply. I trust the
> > power supply meter.
> >
> > Somewhere I read where this was caused by a ground loop within the
> > Omni 6 and there was a cure but I have no idea what it was.
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