One problem I see with tracking line noise using any HF DF-ing scheme is
the ease with which the HF component of line noise couples and
re-radiates from power lines hundreds, or even thousands of yards from
the source -- with lobes and nulls all along the way that make you think
you're hot on the trail when you're not even close. A sharp HF antenna
might find several apparent lobes for a single noise source, leaving you
no closer to the real source than walking under a mile or three of line
carrying an AM BCB radio.
The point of refining the search using an AM-capable receiver at VHF or
UHF, as I understand it (and as it is described in Marv Loftness's book,
POWER LINE INTERFERENCE HANDBOOK), is the increasing resolution as you
move to higher frequencies. If you lose the source when you move from 40
M to 2M, maybe it's because you aren't as close to the source as you
thought you were. It may be helpful to move from 40M to 10M, for
example, refining the location, and then into the low VHF range, as you
get closer, and up into higher frequencies, etc.
If you keep getting ambiguous locations at a higher frequency, maybe you
have multiple sources. Loftness and others have said that is very
likely, anyway, since the conditions that produce arc on one pole
probably apply to all poles in a system that are of the same vintage.
Pick one source, narrow it down, and then go to the next one. Be ready
for peeling back the layers of an onion, finding and quieting one
source, which allows you to hear the next one, etc., ad nauseum. And, be
willing to accept something short of perfection, unless you want to
spend all your time hunting line noise, and no time operating.
Good luck,
Tom, KT9OM
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