Gentlemen -
No amount of adding low-pass filters, inserting antenna tuners,
grounding your set, etc. will clear up these problems. Don't let
anyone tell you different. Facts is facts, and that's that.
While all these steps are good things to do, and follow what is commonly
known as "good amateur practice", the problem is outside the
radio-amplifier-antenna "package". This sort of problem is caused by
the strong signal from your transmitter overloading the audio amplifier
circuitry in the powered devices. There is nothing you can do at your
own station, other than running much lower power, to reduce the problem.
Consider this: The speakers and headphones, wired telephones,,
intercom systems, etc. are by definition, not designed to receive radio
signals directly. Ergo, they are malfunctioning in the presence of
strong RF fields. The problem is created inside the device by the
strong RF field that your antenna (hopefully) is radiating.
Manufacturers of consumer devices, in their attempt to be competitive
(and to maximize profits) tend to leave out the parts that would prevent
this type of problem. They take the chance that their product will not
end up in near proximity to a ham transmitter (or other strong RF
source) . This gamble works often enough that they get away with
sub-standard construction, plus they count on the scenario that the
general public won't understand the real problem, and blame it on the
poor ham. In other words, they prefer to skate on their
responsibilities by shifting the blame to someone else, anyone else,
rather than doing their job.
The fix, both for your own equipment and the neighbor's stereo,
telephones, etc. is to install filtering or suppression devices on each
device that is experiencing problems. Installing ferrite RFI
suppressors in series with speaker or headphone leads, wrapping the
cables around ferrite rods or cores, capacitors across speaker leads
(also from each side of the speaker connection to ground), and similar
techniques are what is required.
A PR problem exists here. It is difficult to get a consumer to
understand why his brand new (whatever) is malfunctioning. The problem
happens only when you transmit, so it must be a defect in your station.
The PR problem lies in convincing the poor neighbor that while you are
the cause of the problem, it is not your fault. A fine definition to be
sure, and one where you r local club's RFI committee can help no end.
No club or RFI committee? Start one, and become the local expert. Once
your have solved a couple of cases, you become the "guru", and your word
will be taken as gospel.
As an aside, also remember that SWR or other mismatch issues will not in
itself increase interference problems, other than in extreme cases high
SWR might have the effect of reducing interference because it causes the
applicable transmitter to back off it's power output so much that little
signal is reaching the antenna - but then nothing is left to make
contacts either!
- Jim, KL7CC
Jack Regan wrote:
Dick,
I have an 811-H connected to my K3 running 500 to 600 watts cw. I have
"problems" that might be similar to yours. I get loud, fuzzy, cw tones on
both my noise canceling head phones my external speakers.
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