[RFI] Power line noise (Ash Thornton)
kimo at lava.net
Mon Feb 8 13:48:38 PST 2010
If I may reiterate advice from Mike Martin, K3RFI, a professional in the
field of RFI sleuthing. He does not recommend that anyone strike a utility
pole to see if you can interrupt or affect the received RFI. He said he
arrived on scene one time and stopped a utility worker from striking the
pole's guy wire. There was a loose HV wire that could have dropped onto that
guy wire, potentially electrocuting the worker. Having said that. I have
spent time with binoculars studying the pole in question to look for any
possible danger such as that (also no termite damage - another problem
here). Then, with an escape plan in mind and two other people nearby plus
wearing a hard hat, I used a short 2 x 4 as a strike plate and a mallet to
shake the pole which caused the RFI to break up. I called the pole number in
and the utility fixed it. They have also replaced transformers closer to the
station in other situations. Whether they were the actual problem or
something associated with the work I cannot say. We get ocean salt spray
build up and subsequent rusting and failure of hardware (and rusting
With your cold weather clue it sounds like you have thermal contraction
allowing a connection to become loose. They also may not be able to see the
arcing in the daytime. Sometimes the copper ground wire may be loosely
touching some other ungrounded hardware on the pole on its way down. Also,
metal clamps securing the wire against the pole may need to be replaced or
at least moved to fresh wood with new screws to hold them in.
Our utility, subsequent to our several issues over the years, had Mike come
out to teach them how to sleuth RFI. They also purchased recommended test
equipment. Our issues preceded that and they realized we knew more about it
than they did so they took us at our word and fixed the problems where we
pointed it out. Mike also gave a free short lecture to local hams on the
Kimo Chun, KH7U
Delta Communications, Inc.
Date: Mon, 8 Feb 2010 14:51:54 EST
From: Jimk8mr at aol.com
Subject: Re: [RFI] Power line noise
To: rfi at contesting.com
Message-ID: <10937.3ce5b9d.38a1c55a at aol.com>
Content-Type: text/plain; charset="US-ASCII"
My experience is that line noise does not drop off quickly at the lower
frequencies. I wonder if you are just hitting some resonant hot spot where
the HF noise peaks because of the RFradiating properties of the power line.
You really do need to move your search up in frequency. I find that six
meters is a prime band for power line noise. Good for finding noise, not so
good for operating there.
I like to do line noise chasing from my bicycle. (Yes, I know it's a bit
too cold and white in Boston right now :>) ). I have an ICOM IC-R10, with
a 2M 5/8 wave mounted on the metal rack in the rear. I program a frequency
for each ham band, 160M through 432MHz, with AM detection. Then I can
easily switch between bands. I find that on 10 or 6 meters, I hear noise
several hundred yards away. Maybe a hundred yards away on 2 meters, and
pretty much just from one pole on 432.
I also carry a 5L 432 yagi that I can hook up when I find a suspicious pole.
Aiming that, I can with confidence pick out a bad pole. Most, but not all,
problems can be heard at 432.
I also use my FT-7800 in the car, again with an AM detected frequency on 2
meters and 432. I have some noise problems from the car on 2M, but a driveby
of a noise source on 2 meters usually shows up +/- 3 poles or so. On 432
it's +/- one pole.
I also have a W1TRC ultrasonic noise detector, which adds a whole extra
level of detection confidence. But that's another story.
73 - Jim K8MR
In a message dated 2/8/2010 2:26:12 P.M. Eastern Standard Time,
w6yn at juno.com writes:
Using a higher frequency is helpful in pinpointing the problem. This noise
is very wide spectrum.
I use 33cm am equipment for this purpose as HF signals travel well along
The possibility of a ground wire on the transformer pole will make the
RFI appear louder when sampled at ground level near the pole.
Transformers are rarely the cause of RFI. An internal arcing may not be
detected with an ultrasound detector.
Transformers are often suspected because it's "the biggest thing up there."
Any loose connection in close field proximity to the HV circuits can cause
sparking between the metal parts.
Wooden construction may shrink over time and just tightening the hardware
can solve this problem.
Sometimes striking the affected pole (Watch your head! Junk may fall.)
with a large hammer or mallet can change or even temporarily stop the
73, Don, W6YN
---------- Original Message ----------
From: Ash Thornton <thorntonash at comcast.net>
To: rfi at contesting.com
Subject: [RFI] Power line noise
Date: Mon, 8 Feb 2010 13:36:08 -0500
I found the posting from Corn country interesting.
I have a situation that also seems to appear with the cold weather,
appears to be limited to a stretch of poles that dead end near my
QTH. I found it with a loop cut for 7Mhz and a K3. Several other hams
in the local neighborhood have the same noise problem I am seeing,
160-40. I see S9 +20-30 noise under several poles and then drops off
rapidly as I move along the line.
NStar the utility her near Boston has been checking this problem for
several weeks. They use a ultra sound detector which has shown
nothing. Several of there grounds are suspect and they will add
additional grounds. A question, anyone know how to recognize a pole
transformer failing?The noise seemed to peak on an AM radio just
under one of them. NStar is coming back tomorrow to look again before
they send out a maintenance crew for the grounds. I am getting a
little worried because if it is not a ground problem they are saying
nothing they can do as they see no arcing.
More information about the RFI