[RFI] DFing intermittent connection

[Steve London]

I would like to thank everyone for their helpful suggestions. It's nice to
have a name for this: PIM (passive intermod).

With the help of my wife providing feedback listening in the shack, I have
done a lot of work (and climbing) over the past few days. Whacking what
elements I could reach with a PVC pipe was inconclusive. I have a 15+ year
old installation with 3 antennas and 2 rotators, so it's safe to say there
are multiple sources of PIM. All the antennas seem to be solid, although I
do wonder about things like the 40M4LLDD (4 element 40) element trusses -
there are rusting turnbuckles in contact with rusting thimbles.

What did seem to make a big difference was the 40 year old thrust bearing.
I loosened the 3 very rusted screws and spun the bearing a number of times.
I then tightened the screws. The PIM isn't 100% gone, but it's much better
than it was. The right answer is to replace the thrust bearing, but that's
a project involving at least removing the 80 rotatable dipole and 4 element
40 from the mast.

73,
Steve, N2IC

On Sun, Aug 8, 2021 at 1:18 PM Steve London <n2icarrl at gmail.com> wrote:

> This is a little off topic from the usual, but the expertise in DFing on
> this forum is outstanding.
>
> I am a serious contester, and do lots of SO2R. That means I need to be
> able to listen on one band while transmitting on another band. With filters
> and stubs I have brought the harmonic and overload energy down to
> acceptable levels. However, I have recently developed a new problem.
> Something on the tower is intermittent and causing the level of the 2nd
> harmonic to vary many S-units as the wind blows or I turn the rotator on
> the 40 meter beam. When this happens it creates hash across the band. I
> have looked for the obvious, but no luck yet. Yes, it could be something
> loose on the 40 meter beam hardware, but before I take on the project of
> taking it down, I would like to pinpoint the source. I am a tower climber,
> so I can get close to everything on the tower. What are the options for
> something handheld, very directional, and not overloaded by the fundamental
> ?
>
> 73,
> Steve, N2IC
>