I chased a similar problem in my Omni-V a few years back. It turned
out to be a TR switch problem. You can test this idea by pulling the
input to the Rx board, or even switching to the Rx antenna using the
slide switch on the back panel.
As I remember, the circuit uses a little RF from the Tx signal to
make a voltage to cut off the diodes fully. I think I found that
even lead dress around the LPF board and PA module had a lot of
effect upon the performance of the TR switch. I'm sorry that I
don't remember more specifics and I didn't make notes. I suspect
that a few well placed ferrite beads may make the thing a bit less
fussy.
My fix, as I remember, was to get the drawing for the Omni-VI
and make the TR switch look like that model. I have done that
with a lot of circuits in my O-V and have had generally good
luck in doing so. There are not a lot of changes between the
O-V and the O-VI but they are in a sense "perfections" of a
pretty dern good design.
de K8RYU
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