Hi, Kim.
Long time no chat. I trust all is well with you.
The noise you are hearing "again' could be a recurrence of the orginal noise or
be a new one. Keep that in mind as you are looking for the source.
For power-line noise, I have had mixed results with DF loops. From far away,
there is a null in the receive pattern of the loop, but when you get near a
source on an overhead power line, it is being radiated by the entire line, so
even if you put the null on the line nearest you, the line up and down the road
is not in the direction of the null, so the null is not very pronounced.
Although one could, in theory, state that power-line noise caused by a power
company is their responsibility to fix, in practice, the more the ham can do to
to find his or her own noise, the more likely it is that the power company can
try to fix it. (I'll say more on this in a follow-up post.) So if possible,
keep trying to pinpoint the source.
In general, one uses the crude DFing provided by the ham's directional antenna
(if he or she has one), then as one gets closer to the source, going up in
frequency is often effective. The final DFing to a pole is typically best done
at 300 MHz or more. Of course, in some cases, the ham doesn't have a
directional antenna, so the only way to go finding the noise is to head off in
different directions, doing one's best to interpret a wildly varying S meter as
it peaks and dips with the standing waves. This is best done with two people --
one to drive and the other to watch the level of the peaks on the S meter and
try to identify the strongest.
Power line noise at the upper end of HF and into VHF and UHF is radiated
quickly by the line, so noise that you hear on 3.5 MHz at your station will
possibly be inaudible or weak on UHF at your station, but when you are close,
you will hear it higher in frequency. This can also be used to good effect in
your mobile search, if you can use 10, 6 or 2 meters to find the general
vicinity of the noise. Use an AM-mode receiver, not an FM receiver. An AM
detector is best, as it will let you hear the 120-Hz buzz that is almost always
part of the power-line noise.
If you have a directional antenna, start in the direction indicated by your
station. This can be somewhat deceptive, however, as many hams report that the
noise peaks on the power line in front of their houses, even though the noise
is somewhat up and down the line. It is radiating all along the line, so the
part closest to that ham is stronger the direction of the actual source.
Drive around, listening on different bands, looking carefully at the power
meter. When you find the point where the peak(s) are strongest, you are
typically near enough to the source to be able to hear it on VHF.
Even on VHF, you may hear it at several poles. With a directional antenna, you
can still pin it down. Stand across the street from the suspect pole. Point a
directional antenna on 300 MHz or higher at the pole and get an S meter
reading. Now, go up or down the line to the next pole. Stand the same distance
from the pole, in the same orientation and pont your antenna at the pole. If
the S meter reading is higher, you are headed toward the source (or at it
already). Go to the next pole. If the S-meter reading is lower, the 2nd pole
is the source.
I have, surpisingly, also been able to pinpoint sources with no more than a
2-foot untuned whip, an AM receiver and a step attenuator. As an example, on
one "service call" I did for a ham while in the area anyway, I did find that a
nearby street around the corner from the ham had a very strong noise that was
S9+ for a large distance down that road on 3.5 MHz with a resonant whip. With
a 2-foot antenna instead of my resonant whip, the noise dripped to about S8,
and was heard for a somewhat shorter distance along the line.
I first drove the road, having the ham give me reports on where the S-meter
seemed to be strongest. I then went to that location and cranked in enough
attenuation so that I heard ONLY receiver hiss. I then decreased the
attenuation so that I also heard just a bit of 120 Hz buzz rising about the
receiver noise. I cranked up the volume and drove the road again. Now I heard
the 120 Hz for only a few poles. I estimated which one was strongest, and
repeated the process. Sure enough, I heard it only when driving past that
particular pole.
The pole ran to an auto repair shop. The shop was closed, but we drove up the
driveway and using the same techniques I found that the noise was strongest on
a pole just outside the building. (I used the same "equal distance" technique
used to pinpoint poles along the road, seeing what level of step attenuator
results in "just heard" noise at equal distances from the building, poles and
other suspect locations.
Hams do need to be careful in finding power-line noises. It is very likely
that there are numerous noise sources near the ham, not all of which can be
heard at his or her station. A strong noise that is coupled onto the line can
be heard for quite a distance down the line, but there may be other noise
sources in between that the ham can't hear at home. Asking the power company
to fix these other noises is very counterproductive, because after they fix a
few of them to no net effect, they become discouraged, or defensive, starting a
downward spiral that is hard to get back on track.
Noise sources can also be present in homes, and the power company is not
responsible for fixing noise put onto the lines by non-power-company sources,
even if the radiation is from the lines.
Hams may also hear multiple noise sources, and until they are all fixed, the
ham still has interference. These sources can be a mix of power-company and
neighboring homes' noise sources. This can be the hardest nut to crack, because
a power company may fix a noise source or two, but the ham may not report any
more than "the noise" is still there. In reality, it is likely that fixing one
of the sources made SOME change, either in noise level or in the nature of the
sound. Of course, until all of the noise sources are fixed, the ham still has
power-line noise.
All of these can be sorted out using a signature technique, essentially looking
at the noise on a oscilloscope at the ham's station, saving the trace then
comparing that trace to noises found in the field. This is easiest with a
single source, but a skilled investigator can sort out multiple sources.
ARRL has a web page or two that has a lot of good information. At the risk of
repeating an earlier post:
http://www.arrl.org/power-line - general power-line resource page. Scroll down
the links on the left to get to the actual FAQ page and other links:
http://www.arrl.org/power-line-noise-faq-page
http://www.arrl.org/information-for-electric-utilities
http://www.arrl.org/fcc-enforcement-involving-electric-utilities
and:
http://www.arrl.org/power-line-noise - multipart article on power line noise
Above all, stay calm. Even the best-intended utilities don't know what they
are doing all of the time and even at best, the priorities given to radio noise
are pretty low on their list. Worst case, utilities will drag their feet and
try not to fix the problem, firm but polite persistence and some patience is
required in all cases. I'll see if I can do another "op-ed" post later this
week to summarize what issues get in the way of resolution, but in the
meantime, I will note that every cuss work directed at utilities, ARRL staff or
FCC will make it LESS likely that the problem will ultimately get resolved.
73,
Ed Hare, W1RFI
ARRL Laboratory Manager
225 Main St
Newington, CT 06111
Tel: 860-594-0318
Email: W1RFI@arrl.org
________________________________
From: Kim Elmore [mailto:cw_de_n5op@sbcglobal.net]
Sent: Sat 10/9/2010 2:39 PM
To: rfi@contesting.com
Subject: [RFI] Power Line Noise Conundrum
I have a recurring power line RFI issue. At one point, it seemed to
have been remedied, but has returned. It sounds similar to what I had
earlier in the spring. That was repaired by the power company along
with the help of a tornado (really!).
Now, though, I hear it again.
Trying to be helpful, I'm trying to track it down and have had
confusing results. First, I've tried chasing it with my rotatable
antennas as home. I have K9AY loops that have a good null off the
back. I laso have a 2 el 40 beam, along with a 20 m-10 m tribander
and a dipole for 30 m-12 m. Depending on the time of day, I hear it
pretty much everywhere relatively well, save for 20 m, which seems to
be the quietest.
On 80 m with the K9AY loops, I have minimum noise when the null is
either SW or NE; which strikes me as inconsistent.
On the 2 el 40 m bean, I get deep, narrow nulls off of what i believe
to be the sides when it is oriented either N or S. I also get a
weaker null when it's pointed roughly W, indicating the source is to my East.
I don't hear much noise on 20 m. On 15 m I get a null to the N, but
on 10 m I get a null to the S! the antennas work as they should (CW
signals are peaked when the antenna is pointed at their source).
Using the dipole, I get weak nulls when it's pointed N or S.
I have a corner reflector for 2 m and 70 cm but cannot hear anything
on either band when I use AM detection regardless of where it's pointed.
I drove around the area in my car, using my dual-band rig set for AM
detection. Using 2 m, I tended to hear it over a broad stretch along
a road that is about 1/2 mi to my east. I found a localized source to
my ENE when I went up to 70 cm. I suspect that is the source, as it's
very near a pole that carries quite a bit of hardware (lots off bell
insulators and lighting arrestors) and what appears to be a 25 kV line.
But I'm perplexed about the inconsistency I hear using my HF
antennas. Is this because of standing waves along the lines, or am I
hearing different sources? And, how can I use this to be most helpful
to the power company? They were very helpful the last time and I
don't want to send them on any wild goose chases.
73,
Kim Elmore N5OP
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