[Elecraft] OT--RFI Issue
ab2tc
ab2tc at arrl.net
Wed Mar 20 19:19:43 EDT 2013
Hi,
Please indicate a source of twisted pair wire suitable for speaker feeds.
#16 or #14 is fine for me. I am still having trouble keeping my 15m signals
out of my family room system. Currently that room's speaker wire is of the
parallel kind.
AB2TC - Knut
Jim Brown-10 wrote
>> Your position should be to offer to assist a qualified technician in
>> >isolating and correcting any deficiencies by providing periods of
>> >operating to test the results of any repairs.
>
> I'd say it depends entirely on the attitude of the RFI victiim, and the
> ham's relationship with that party. The vast majority of RFI complaints
> today are the result of Pin One Problems in the victim equipment. These
> are a manufacturing defect that is the result of poor design, and any
> wiring connected to the equipment will act as a receiving antenna for
> our signals, where they will be rectified and amplified.
>
> In today's world, "qualified technician" for consumer electronics is an
> oxymoron.
>
> Several years ago, I helped ND2T diagnose and cure strong RFI to his
> next door neighbor's "exotic high futility" system, in a living room
> only 20 ft from Tom's antennas, which were driven by a big ACOM legal
> limit amp. Tom introduced me as an audio expert and RFI expert (which I
> am) then returned to his shack and transmitted on all the bands. I stuck
> chokes on cables until the RFI went away, and by the time Tom arrived
> after our work was done, had the guy ready to open his wallet to buy
> them at my cost. Tom, however, insisted on paying for the cores
> himself. Problem solved.
>
> It is NEVER a good idea to modify the equipment, but it IS good to
> disable the antennas (that wiring) by adding ferrite chokes tuned to the
> transmitter frequency(ies). Tuning is accomplished simply by using the
> "right" ferrite mix and adjusting the number of turns through the core.
>
> Speaker cables are a very common antenna. Another excellent move is to
> replace parallel wire loudspeaker cables (zip cord, no matter how
> exotic) by twisted pair. #12 copper makes excellent speaker cable
> (there's a classic AES Paper by Prof. R. A Greiner, Dept of EE at U Wis
> about this), and twisting strongly rejects RF coupling. I have solved
> MANY cases of RFI by doing this.
>
> RFI causes and solutions are covered in considerable detail in
>
> http://audiosystemsgroup.com/RFI-Ham.pdf
>
> 73, Jim K9YC
> <snip>
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