Thanks for all the suggestions. Unfortunately, magic DFing equipment for HF
must not exist, or someone would have suggested it.
There are a lot of things it could be. To narrow it down, I would have to
take down a rotatable 80, 4 el 40, and KT-36XA and hope I find a smoking
gun.
For your entertainment, here's a short video of the PIM:
http://www.kkn.net/~n2ic/pim.mp4 .
73,
Steve, N2IC
On Sun, Aug 8, 2021 at 3:24 PM <donovanf@erols.com> wrote:
> Hi Steve,
>
> Does the RFI affect only one antenna on receive or multiple
> antennas?
>
> Suggest you have someone visit your shack and listen on the
> harmonic frequency and observe your spectrum display on the
> harmonic frequency as you jostle things up on the tower.
>
> Not as effective -- because you can't remotely watch as S-meter
> or spectrum display on the harmonic frequency -- you could listen
> to your receiver audio through a cell phone or handheld transceiver.
>
> Possible causes:
> - worn coax cable loop from constant rotation or wind exposure.
> You should be able to observe this on your TDR from inside your
> shack if you own a TDR. If you don't own a TDR, purchase one!
> Its one of the best tool investments you'll ever make. Reflected
> power may also vary if the coax is severely worn.
>
> - arcing inside your thrust bearing
>
> - arcing ring rotator surfaces
>
> 73
> Frank
> W3LPL
>
>
>
> ------------------------------
> *From: *"k1ttt dave" <k1ttt.dave@gmail.com>
> *To: *"Steve London" <n2icarrl@gmail.com>, rfi@contesting.com
> *Sent: *Sunday, August 8, 2021 7:48:00 PM
> *Subject: *Re: [RFI] DFing intermittent connection
>
> I would go up with a long pole (preferably fiberglass or some other
> insulator) and start whacking things to see if you can stimulate it. Also
> pull and push on all the cables, check that connections are tight, look for
> rubbed through insulation on rotor loops, etc. I had one once that would
> generate a sub-harmonic, 20m tx caused 40m subharmonic and then also 15m
> 3/2's harmonic, must be a puncture in hardline jacket somewhere that would
> arc and excite a resonance in a certain length of hardline... adding ground
> connection to the connectors at the top of the tower stopped it. I had
> been
> hunting it for weeks with all sorts of tools and wouldn't have found it if
> I
> didn't push and pull on the (totally unrelated to 20m or 40m) cables while
> someone was monitoring it.
>
> David Robbins K1TTT
> e-mail: mailto:k1ttt@arrl.net
> web: http://wiki.k1ttt.net
> AR-Cluster node: telnet://k1ttt.net:7373
>
>
> -----Original Message-----
> From: RFI <rfi-bounces+k1ttt=arrl.net@contesting.com> On Behalf Of Steve
> London
> Sent: Sunday, August 8, 2021 15:19
> To: rfi@contesting.com
> Subject: [RFI] DFing intermittent connection
>
> 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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