Topband: Local noise environment

[Brad Rehm]

"It may be only coincidence that I have a 500 kv line in that
direction."

"73, Pete N4ZR"

Pete,

Mike's comments seem to be right on the mark.

As a matter of interest, here are some observations we've made in
doing work for my company on HV transmission line noise:  We learned,
at the outset, that you can often see problems on these lines by
looking at the insulators with a pair of binoculars.  They're often
covered with bird doo-doo or visibly broken.  (I've got a pair lying
on the floor in my office, and several of the ceramic disks have been
blown apart.)  You might want to visit the lines and take a look at
the insulators on a few of the towers.

The power companies normally survey these lines once or twice a year
to look for problems so that they can schedule maintenance on specific
towers.  If your noise has appeared recently and it's emanating from
that line, they may find and fix it in the next service round without
you're doing anything.  Your spotting hardware that's definitely
off-spec would be appreciated, though.  At least, it would be if you
were dealing with the guys here in central Texas.

I've also found it very interesting to listen to HV line noise with a
portable receiver.  My FT-817 has been very useful for this.  It's
interesting that each of the lines I've looked at has different
emissions spectra.  Some radiate in the 300-400 kHz range.  Some are
up around 2 MHz.  Others are very strong, beginning at 10-11 MHz.
Listening at UHF frequencies hasn't produced any helpful information
so far, although listening there has been very helpful in dealing with
low-voltage lines.

We've used a number of different antennas for this work--a loopstick
with preamplifier; an 8-turn loop with preamp; a longwire.  All of
this equipment has been used on the ground and on an aircraft.

I've also built a 1:9 balun and clamped leads from the low-impedance
end of the balun to legs of transmission towers.  The assumption here
is that leakage currents around or across the insulators find their wa
ys to ground through the tower legs.  This method is very effective in
confirming that there's an insulator failure on a particular tower.
If you try this, you'd better do it with the consent of the power
company.  I've been observed suspiciously by locals who thought I was
a saboteur.  Got away before the Homeland Security force arrived to
label me an enemy of the state and ship me to Guantanamo.

Lots of luck finding the source.  Looks as if you're getting good
advice.

73,
Brad, KV5V