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Elevation-dependent Interference

This is wierd.  Do I have defective foliage, or is this
to be expected?

I've been having trouble with desense on AO-40.  Transmit
on 70cm, and the 2.4 ghz noise floor rises so far I can't
hear anything else.  Found some bad connections and a bad
set of relay contacts; thought it was fixed.  But earlier
this week it came back.

After some experimenting, I find that as the Elevation
heads towards the horizon, the desense problem rises.  As
the elevation rises, the problem goes away.  Above about
20 degrees, it's essentially gone.  Nice and smooth (not
due to a bad cable at the rotor).

Now, this isn't the ground (thermal) noise I'm picking up.
It's only there on transmit.

Any ideas why this is happening?  Any fixes?

Greg  KO6TH

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