Hi Steve,
Do you hear this RFI on every antenna?
Does it occur on only one transmitting antenna?
Small "magnetic loops" are excellent for local DFing and you can
build one in about an hour
73
Frank
W3LPL
----- Original Message -----
From: "Steve London" <n2icarrl@gmail.com>
To: rfi@contesting.com
Sent: Monday, August 9, 2021 8:54:49 PM
Subject: Re: [RFI] DFing intermittent connection
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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