[RFI] Line Noise

[Wescom, Gary]

Tom,

Yours sounds a lot like the problem I had a few years ago.  Like you, I
had no luck getting the power company folks to locate and fix the
problem.  This is in spite of the fact that I work for the utility
myself (in the computer group).  What I ended up doing was to find the
problems myself and turn them in to the "TVI" guy one at a time.  If you
can identify the exact pole that is having the problem, you can normally
get things fixed pretty easily.  Power companies have a legal
requirement to not radiate noise so normally have special funding to fix
these problems that is outside the normal maintenance accounts.  The
thing to remember is that most power company forms and documents list
any form of power line interference as "TVI".

Again, like you, I had little success finding problems using an AM band
transistor radio.  I had much better success using a cheap aircraft band
portable.  108 to 136 MHz aircraft communications uses AM so receivers
for that band have AM detectors.  Line noise is much shorter range on
VHF so you normally have to be much closer to a noise source to detect
it.  My best results was with a home-brew tunable HF am detector but the
aircraft band receiver is almost as good.

What you are looking for is loose hardware on the poles.  The primary
noise source is usually slack bell insulators.  Those bell shaped
insulators you see at the ends of power line runs have metal parts
which, if not electrically bonded, will arc at a 120Hz rate.   Without
sufficient tensioning, a thin oxide layer builds up in metal joints.
They arc simply because they are in such close proximity to high voltage
(usually 4, 7.5, or 12 KV!). You can spot slack bells quite easily since
they usually sag under their own weight.  If the line they are on was
properly tensioned, they wouldn't sag.  Bell insulators are supposed to
have metallic spring clips or soldered on jumper wires to prevent arcing
but occasionally these things are damaged and no longer make contact.

Another common source of pole top arcing is just loose hardware.  Any
kind of metal-to-metal contact, such as nuts, bolts, brackets, and
braces, can loosen from the shrink and swell of poles with weather
changes.  When loose, oxide layers build up and arcing begins.  Even
though not directly connected to the power lines, these arcs can be so
powerful that they couple into the line and propagate for miles.  It is
not uncommon for loose nuts and bolts on a pole top to loosen and arc so
badly that the pole catches fire.  Obviously, noise that goes away when
the poles are wet and comes back when the poles are dry is a good
candidate for loose hardware problems.  It is a common task for a line
maintenance crew to tighten hardware on pole tops.

Transformers are rarely the source of line noise.  I actually found only
one noisy transformer and it was simply a loose high voltage connection
to the top of the transformer.  I could wiggle the guy wire on that pole
a little and see the wire wobble.  Noise burst were produced as the wire
wobbled.

What I do to locate a bad pole is to first narrow the search area down
to a few poles.  I then carefully inspect the poles with binoculars for
obvious loose or broken hardware.  I then lightly kick suspect poles to
see if the noise is changed or modulated by pole vibration.  Unless the
base is really stout, I just turn my back to the pole and give it a mule
kick.  I have found a number of bad poles this way.  The farthest
distance from my home that I bothered checking was about half a mile.
Some louder sources could travel several miles on the lines though.

If I am having trouble narrowing my search down, I sometimes resorted to
another trick.  I would go to a convenient pole guy line and gently
wiggle it to get the power lines to start swaying a little.  Sometimes,
loose hardware would on a conductor run would show up from the line
movement.

One thing to watch out for, aside from the obvious danger of just being
around power lines, is that you are not fooled by the noise peaks you
will find near pole ground lines, guy lines, and other conductors
running down poles.  These things bring power line noise right down to
you so might make you think you have found a source when all you have is
a noise antenna.

Once you find a bad pole, write its address and any identifying numbers
you can spot on it and turn a "TVI" report into the power company.  The
thing to watch though, is that your report may not be written down
correctly,  The folks you talk to at the power company don't normally
understand RF or think that anyone besides their own technician is
incapable of understanding such an arcane subject.  Try to get them to
contact you and, preferably, allow you to be present when the work is
done.  If your problem report is just handed to a utility line repair
foreman, he is likely to simply go to your home address and decide that
he can hear the ball game on his truck radio just fine so not bother
checking any further.  You want to be able to give him the correct
repair information so he will actually work on the real problem.

Don't be discourage if getting one problem fixed does not make much
difference.  I probably had to have 6 or 8 poles fixed before things got
noticeably better.  I have had several years of relatively quite power
lines now so the effort I put out was worth it.  Good luck.

> ----------
> From: 	thomas@cybrzn.com[SMTP:thomas@cybrzn.com]
> Sent: 	Saturday, February 28, 1998 6:23 AM
> To: 	RFI@Contesting.Com
> Subject: 	[RFI] Line Noise
> 
> To All:
> 
> Wondering if anybody has experience locating noise generated by power
> lines?
> I have a nasty s5 noise level on 10,15 & 20 mtrs. This noise is
> present
> 24 hours per day, and I can peak it with my beam in a specific
> direction. It is worst when weather conditions are dry, and will
> disappear completely when weather is wet. The power company has been
> out
> here at least 5 times, and they claim they have checked out a 10 mile
> radius. As far as they are concerned, the case is closed and they have
> refused to do anything further. I have tried walking the lines with a
> transistor AM radio, but I seem to get noise all along, and unable to
> pinpoint it to any particular location. To top it off, it is worst at
> a
> beam heading of 45 degrees! Not good for a contester.
> Any help would be greatly appreciated.
> Tearing my hair out,
> Tom Hellem K0SN
> Porterfield, Wi.
> 
> 
> 
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