On Mon, 28 Jun 2004 13:29:54 -0400, Tom Berry wrote:
>The only solution I have been able to find is to turn them off. I
>have tried coiling the power cord, beads on the power cord and I even
>tried plugging them into my computer UPS system which I think will
>isolate them from the AC line.
Nothing you have described is likely to have any effect at all at HF. Assuming
that the
trash is getting onto the power line, you need far more serious filtering than
you have
described, and filtering that is specifically tailored to HF. Beads in general
are useful
only at VHF.
A starting place for a common mode power line choke for 14-30 MHz would be 2-8
turns around a 2.3" OD #43 toroid. Power line filters such as those sold by
CorCom
can also help. For any of these filters to be effective, the equipment, the
filter ground,
and the outlet ground need to tied together at the frequencies of interest.
BTW, don't just hang a filter and ground wire on this thing and call it a day.
If the filter
couples the noise onto a long ground wire, it can act like an antenna and
radiate the
noise. That's a good reason for having the series impedance to form a divider.
For an example of this, have a look at
http://audiosystemsgroup.com/NoisyPole-Wide.JPG
and
http://audiosystemsgroup.com/NoisyPole-CloseUp.JPG
This is the pole that services our former AT&T site at W6BX (see qrz.com).
Something at the top of this pole is conducting HF noise onto the several
ground
leads, and every one of them is hot with the noise. I strongly suspect that it
is the
downleads (that is, the grounds), not the power lines, that are radiating the
noise.
The fix, of course, is to eliminate the noise at the source.
Jim Brown K9YC
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