Back when I first got back on the air, lots of neighbors used "rabbit ear"
antennas for TV. After much investigation, it became clear that they were
picking up harmonics from every metal on metal connection in the neighborhood.
Those with rooftop antennas never had a problem. I suspect even nails in the
walls near the TV could do it.
73,
Scott K9MA
----------
Scott Ellington
--- via iPad
> On Aug 11, 2021, at 1:27 PM, Steve London <n2icarrl@gmail.com> wrote:
>
> 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@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
>>
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