[RFI] DFing intermittent connection

[k1ttt.dave at gmail.com]

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 at arrl.net
web: http://wiki.k1ttt.net
AR-Cluster node: telnet://k1ttt.net:7373


-----Original Message-----
From: RFI <rfi-bounces+k1ttt=arrl.net at contesting.com> On Behalf Of Steve
London
Sent: Sunday, August 8, 2021 15:19
To: rfi at 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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