Very good info. This is one to save!
Thanks.
Tom - W4BQF
----- Original Message -----
From: "Mike Hyder -N4NT-" <mike_n4nt@charter.net>
To: <tentec@contesting.com>
Cc: <csturner@kcbx.net>
Sent: Tuesday, July 13, 2004 1:48 PM
Subject: [TenTec] noises
> Guys, I wrote this and a friend posted it on his website at
> www.qsl.net/n4tn/noise.html but that site is sloooooooooooow these days.
It
> explains specifics of unique problems and solutions and is intended to
show
> how an open mind and some thought can help find sources of noise. I call
> your attention particularly to Section 1, about "bell-shaped" insulators.
>
> Please tell me of any similar experiences you've had.
>
> Regards,
> Mike -N4NT-
> __________________________________________________
>
> POWER LINE (AND OTHER) INTERFERENCE PROBLEMS EXPERIENCED BY N4NT
>
> 1. The first power line interference problem I ever saw cured was found
by
> a ham named Clyde Goforth WA4NTZ who worked for the Knoxville Utilities
> Board. It was his job to locate and remedy these problems.
>
> I lived in an apartment complex and was experiencing strong interference
on
> 80 and 40 meters which usually began in the morning and lasted until
> nightfall and often later. Rain cured the problem temporarily.
>
> Clyde came out, looked around, and told me he saw the problem right off.
He
> termed it "slack-span interference." I thought he was joking as he pointed
> out the "drop" from the main line to the pole near the apartment building.
> The line was not pulled taut, but drooped between the insulators at its
> ends. Each end of the line was supported by a bell-shaped insulator. The
> line connected at its ends to the open ends of the bells. The other end of
> each bell had a loop which was connected through an eye-bolt which passed
> through the pole.
>
> Clyde explained that where there is enough tension on this mechanical
> connection between the bell's loop and the eyebolt, their metal surfaces
> keep each other clean and make good electrical contact. Where there is not
> enough tension on the line, the corrosion builds up and causes very small
> arcs because of voltages induced or coupled into the hardware. The radio
> frequency energy created by these arcs then passes through the bell just
as
> if it were a capacitor dielectric, and the whole line radiates. In my
case,
> removing the slack from the line by pulling it taut cured the problem,
just
> as Clyde predicted it would.
>
> Since that time I have seen over five similar instances of this type
> interference and all were cured the same way. This problem is most common
on
> residential drops because pulling the wires taut enough to keep the metal
> parts clean puts a force on the pole which may cause it to lean if that
> force is not opposed by a guy wire. By leaving slack in the line, the
> company can avoid putting a guy wire in someone's lawn, and they often do.
>
> Often you can spot these easily by just looking, but it is far better to
> localize the particular pole or drop which is the source of the
> interference. We have had the best success using a VHF single-sideband
> receiver with an S-meter. On HF, the interference travels along the lines
> and can seem just as strong quite some distance from the source as right
> under it. There are also "nulls" between strong signal readings as one
> travels under the lines. This can be deceptive. (Some hams have gone quite
> bald scratching their heads in utter confusion trying to locate a source
> using an AM broadcast radio.) On VHF, on the other hand, the signal is
> rapidly attenuated as the distance from the source increases. UHF might be
> even better, but we never tried that. An aircraft band receiver with an
> S-meter might work but we never tried that, either.
>
> Localizing the interference has kept us from sending the power company
> employees on "wild goose chases," and thus kept our relationship with them
> good.
> _________________
>
> 2. When I first moved to Johnson City, I had very high levels of power
line
> noise. The power company traced it to a lightning arrestor strip atop a
pole
> transformer. The strip had come loose or had bent and was making contact
> with whatever it was supposed to arc to. They were glad to find that one,
> said it could have been dangerous.
> _________________
>
> 3. About 300 yards from my home there was a 33kV transmission line
> supported by wooden poles. The interference it radiated was intermittent,
> but was generally S-9 or higher when present. As time went on, it became
> almost continuous around the clock. A neighboring Ham (Rick VanLandingham
> KF4FL) used his 2 meter SSB receiver to help me localize it to one pole.
Our
> power company had previously tried to find the source, wasting many man
> hours. After Rick localized it to one pole (which I should have done in
the
> first place), we had the power company try again. They could not find the
> problem. Late one cold, clear night when the interference was bad I walked
> out to look at the pole and saw, up near the top, a small spark that
looked
> like a distant star. As I moved around, the spark would disappear and then
> reappear as I returned to my original position. I saw a soda can on the
> ground and used it to mark my vantage point. Then I got Rick, my camera, a
> tripod, and a flashlight and we went back to the pole. I set up the camera
> and opened its shutter. While the shutter was open, I painted the pole
with
> light from the flashlight so it would show up in the photograph. Because
the
> shutter was open for over a minute, the spark showed up clearly in the
> photo. The pole and its hardware were clearly visible, too. The problem
was
> caused by a diagonal steel support, which supported the wooden cross
member
> of the pole, coming in contact with the ground wire which ran down the
pole.
> Apparently enough voltage was being induced or coupled into that support
to
> create the arc. The ground wire connected with the top cable of the three
> wire system and served as the antenna for the interference source. Armed
> with the photo, the power company made quick work of remedying the
problem.
> ________________
>
> 4. One section of Johnson City had very strong interference over an area
> covering several square miles. The lower the frequency, the further out
the
> interference extended. Again using Rick's 2- meter SSB receiver's S-meter,
> we localized the source as a main power station which served much of
Johnson
> City.
>
> We went back at night and this time were carrying camera, etc. We observed
> many little sparks like distant stars above transformer housings, but it
was
> too dark to see the problem. We set up the camera some distance from the
> station with a telephoto lens (to give good perspective) and opened the
> shutter. I walked over to the station's perimeter fence and set off a
camera
> flash to illuminate the station's hardware in our photo.
>
> The power company officials were amazed with the results. The photos
clearly
> showed spring clips mounted atop long insulators holding a bus bar. At
each
> point where the bar passed through the clips, an arc showed in the
> photograph. They called TVA for advice and someone applied a conducting
> grease to those mechanical joints and cured the problem. I believe they
> re-grease those connections on a regular basis now.
> _______________
>
> 5. One spring and summer there began to be an interference which made a
> clicking sound, stronger on lower frequencies, over S-9 on 80 meters. My
> dim recollection is that those clicks came about every two or three
seconds.
> The source was a neighbor's electric fence in "weed burning" mode.
Walking
> the perimeter of the field, we found many weeds/vines/saplings, etc. grown
> up and touching the fence wire. Fixing that one was easy -- we told the
> owner and he bushhogged the whole thing. We didn't have to lift a finger.
> The owner was happy because the fence might not have kept his animals
> confined when grounded out like that.
> _______________
>
> 6. As I remember, this sixth instance of interference was strongest on 15
> meters. It was not uniform in strength as I tuned across the band. I could
> tune to the raggedy edge of it near the low end of the band and below that
I
> did not notice it. The interference was strong, S-9 or stronger, and
changed
> sound as I tuned through it, unlike typical power line type interference.
My
> noise blanker was completely ineffective against it. My recollection is
that
> as I tuned about seven to ten kHz the pattern of sound would begin to
> repeat. It sounded much like power line interference, but had a slight
> difference. The low end of the interference would drift up in frequency.
The
> band of interference was at least 250 kHz wide.
>
> Using my beam antenna, I lined up an azimuth for the interference which
ran
> across two houses in the neighborhood. Beyond them in that line was farm
> land. A friend, Al LeFevere KM4TR, came with a VLF receiver which was
> directional because of its loopstick antenna. Walking on the street
between
> the two houses showed clearly which one contained the source. We went to
the
> door, explained to the man our mission and asked for his assistance. While
> we listened to the VLF receiver, he turned off his circuit breakers, one
by
> one. At last, one of them stopped the noise. He took us to the room which
> was served by that breaker, but we could not find the source of the noise.
> We unplugged a power cube, unhooked his cordless telephone, etc. The last
> device was an innocuous looking small lamp. He touched it, the lamp came
on
> and the receiver went wild.
>
> It was a "touch lamp." Merely touching any metal part of the lamp would
turn
> it from off to dim to bright. We told him that was surely the culprit. He
> said, "You know, that thing has a 'short' in it. It comes on and goes off
by
> itself sometimes." I didn't tell him, but suspect a kilowatt of RF from
next
> door beamed at his "touch lamp" was the 'short.' We volunteered to fix the
> lamp by removing the touch circuit and installing a switch on the lamp's
> base. He loved the idea and turned the lamp over to us. We did a nice job
> with good hardware and returned it to him. He thanked us profusely, and we
> did likewise to him. A win-win situation, I'd say.
> __________________
> xxxx
>
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