Gee whiz -- I go into the hospital for a week and thing go WAY off the
rails! Thanks to W4TV and W3FPR for intelligently moving the discussion
back on track.
Questions:
EXACTLY what is the configuration the the "vertical antenna?
Quarter-wave with radials or half wave without radials? How many
radials? How long?
Where is the antenna feedpoint with respect to the radio? What coax are
you feeding it with? Are you SURE that the connectors at both ends are
properly installed and gas-pliers tight at both ends?
Is there a short, fat copper bond from chassis to chassis between every
piece of gear in your shack? Is there short fat copper from there to
all the other grounds in your home?
Joe is exactly right -- ANY "balun" that isn't multiple turns of coax
around a #43 or #31 ferrite core is USELESS at HF. Those "string of
beads" "baluns" sold by various vendors are badly misguided copies of
the W2DU design, which what a very good design that used a LOT of #73
beads.
Joe is also exactly right -- the ONLY proper connection of a cable
shield is to the SHIELDING ENCLOSURE of the equipment it feeds. The
cable shield should ALSO be bonded to the shielding of the microphone.
Some fundamentals: ANY antenna that "works" will put RF in the shack --
it does that by radiating RF. An antenna that lacks an effective common
mode choke will ALSO put RF onto the feedline.
Summary of suggestions/comments:
Answer the questions I asked above. They are all important.
Download and STUDY k9yc/com/RFI-Ham.pdf and
http://k9yc.com/GroundingAndAudio.pdf
Follow these instructions carefully. I suspect that the cause of Jan's
problem is failure to properly connect cable shields, and/or to bond all
the gear together.
73, Jim K9YC
On Tue,11/24/2015 6:54 AM, Joe Subich, W4TV wrote:
Not true ... the Icom uses an electret mic, not the dynamic Audio-
Technica. If the microphone is wired correctly, the issue is in
the antenna system and probably requires improved common mode
decoupling. Air wound solenoidal chokes are not sufficient in
the most intractable cases *like elevated verticals*.
Replace the elevated vertical with a dummy load. If the RFI is
eliminated, the problem is in the antenna system.
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