After a multi-month struggle involving hundreds of $$$ in ferrites,
rewiring, etc. I MAY have licked my RFI problem.
My headset is set up like this:
Yamaha CM500 headset phones <<----- F3K front panel
mic
V
mic electret power supply
V
1/8" phone jack
V
RJ-45 jack
V
RJ-45 cable
V ferrite here
RJ-4 on F3K front panel
The symptom was most clearly heard as something between IM
distortion and a very high level of near-white noise on MON during
transmit. The amount of interference was pretty well proportional
to radiated power (high SWR reduced the interference for a given
output level), so I figured something the antenna was radiating was
getting in somewhere. The most natural low-level (and therefore
sensitive) spot was the mic input. Finally in desperation, I
unplugged the mic power supply from the 1/8" jack, and the noise
miraculously vanished. It was coming in thru the mic cable (which
already had one ferrite on it). Also the wiring connecting the 1/8"
phone jack was unsoldered and so spark-prone at best.
So I soldered the jack, adding about 1' of leads in the process. I
then installed a three turn ferrite on the jack leads and another
ferrite on the RJ-45 cable. Voila! At least for now, stay
tuned..... What would you all think about adding some serious
chokes on the audio feed line? Do they really belong inside the F3K case???
Yamaha CM500 headset phones <<----- F3K front panel
mic
V
mic electret power supply
V
1/8" phone jack
V added one three turn ferrite here
RJ-45 jack
V added one ferrite here
RJ-45 cable
V existing ferrite
RJ-4 on F3K front panel
--
Dave Gomberg, San Francisco NE5EE gomberg1 at wcf dot com
All addresses, phones, etc. at http://www.wcf.com/ham/info.html
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