Hi Larry,
There is a copy of an extensive report done by Naval Post Grad School on
the ARRL website. Free download;
See:
http://www.arrl.org/tis/info/HTML/power_line_handbook/
The authors have given awesome talks at radio clubs locally about their
extensive professional hands on experience in quieting Military receiving
sites from noise sources, mostly from Power line distribution systems.
Details of techniques and equipment used are in the downloadable manual.
A couple of standout memories of their talks still are in my memory...
One, is a statement that the assumption of dirty ceramic insulators being a
surface subject to arc over or leakage currents that are noise sources is
almost never true.
The observation of lessened noise after rain, is rarely due to rain cleaned
insulator surfaces. Noise sources are often created by loose mechanical
coupling of metal parts(especially rusty) in the pole system. The oxide
layers between metal links (especially the links on multiple disk insulator
chains) offer crude diode junctions that are punctured repeatedly as the 60
hz waveform rises and falls, above puncture voltage. This repeated sparking
is a large contributer to noise at HF frequencies. The most noisy disk
insulator stacks are those that are slack, without heavy loads, due to the
greater possiblity of oxides accumulating between load bearing links.
Similar loose mechanical linkages on the pole (nuts, bolts, ground clamps,
etc) can be similar sources for noise. I think they mentioned that about
2-5 percent of such insulator stacks turn out to be HF noise sources.
When hams sometimes call the power companies to "clean the insulators", the
noise is often lessened or eliminated. The reason is that the soaking of
the metal hardware with moisture Temporarily makes oxides more conductive,
and stops the the sparking. It also causes moisture absorption and swelling
of wooden pole structural members which may tighten (or loosen) various
mechanical couplings, eliminating (or exaserbating) noise sources. The
noise problem has not been solved permanently, and usually the noise will
come back when the poles dry out. Persistence with the power company, and
backed by successful procedures outlined in the navy documents can often get
the power company to eliminate the noise sources.
The Navy guys have pressured/convinced/worked with the power companies to
use a new "Epoxilator" product in place of the old stacks of disks to reduce
noise sources.
Old and noisy; See : http://www.cjow.com/archive/1980/06porcelain10s.jpg
This plastic insulator is showing up all over here on the central coast.
No Noise...
This picure shows both kinds of insulators on a power pole crossarm.
See: http://www.appanet.org/files/images/AppDeadEndEpoxilator4.jpg
At N6IJ a number of years ago, nieve me, suspected a power pole having/
being a noise source, and at night, smacked it with a hammer at about 4 ft
above ground, and saw a huge number of small sparks all over the pole,
repeated each time I hit the pole..scared me (Dont do this, possibly
dangerous as explained in the Naval Docs from ARRL).
Many nuts, bolts, ground wires, braces, etc, (totally unconnected to the
distribution lines, but close within their electrical fields,) were loose
and charged with voltage that sparked whenever the pole was jiggled
significantly. The pole was very old, and spent its life on the Ft Ord
Military Base.
The NPS Professors said the High Voltage towers are rarely a source of HF
radio noise...said leakage, arcs, or hardware defects make themselves known
in a more violent or spectacular fashion, since the energy levels involved
at 100 to 500 kv produce damage that is noticed and attended to rapidly by
the power companies, or the design and implementation is done with close to
zero defects.
See this interesting picture: http://www.sitapolycoats.com/images/img1.jpg
I think Gene's advice below, about avoiding them, if alternatives are
possible is good...
73, DX, de Pat AA6EG aa6eg@hotmail.com;
Skype: Sparky599
>From: ersmar@comcast.net
>To: "Larry Burke" <wi5a@sbcglobal.net>, <towertalk@contesting.com>
>Subject: Re: [TowerTalk] Towers/Antennas Near 138kV Transmission Lines
>Date: Mon, 14 Aug 2006 20:06:37 +0000
>Larry:
>
> I spent my first ten years out of college as an engineer with the
>local electric utility, designing substations, among other things. One
>reason that distribution lines might seem more noisy is there are more of
>them around and the likelihood of having defective or dirty components is
>greater with these LV lines than with higher voltage lines.
>
> You might want to take an AM receiver for BCB/SW and for aeronautical
>bands out to the property sometime and listen on both. They both ought to
>tell you whether arcing (heard as QRN) exists and its extent,
>frequency-wise. Don't visit after a rainstorm, though. The rain will
>clean off much of the contaminents that cause arcing in the first place.
>Go after a few weeks of dry weather if possible. Dirt, droppings, etc will
>have had a chance to accumulate, causing the noise you might pick up on
>your weak-signal receivers.
>
> But if it were my money, I'd spend it on a piece of property that was
>not that close to a power line. The line might be the best maintained in
>the country, but why tempt fate if you have a choice?
>
>GL es 73 de
>Gene Smar AD3F
-------------- Original message ----------------------
>From: "Larry Burke" <wi5a@sbcglobal.net>
> >
> > In my search for property on which to build a new home we have come
>across
> > several lots that are in proximity to 138kV overhead distribution
>systems.
> > One lot, in particular, is within 150 ft of such lines (there's a lot
> > between the one we are looking at and the lines). Obviously, I would not
> > construct a tower/antenna system in such a manner as to come in contact
>with
> > these lines. What is the collective experience of the group. anything in
> > particular to consider or would you steer away from such property
>entirely?
> >
> > I plan to operate everything from 160-2m with primary interest being DX.
> > >From an RFI standpoint I have heard that such lines can actually be
>quieter
> > than residential distribution. True?
> >
> >
> > Larry Burke
> > Friendswood, Texas
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