[RFI] Difficult power line RFI find.
K9MA
k9ma at sdellington.us
Wed Mar 10 15:14:30 EST 2021
Hi Don,
I've had some of those very constant sources, which makes tracking
harder. Usually, they eventually go into some kind of fluctuations,
often subtle ones. In my case, identifying the right source is
particularly critical, as I live in an urban area surrounded by overhead
power lines, with thousands of potential noise sources nearby. I can
only hope to track down the very worst of them, but many weaker ones
always show up when I'm out tracking. That's less likely to happen in an
area with fewer potential sources.
73,
Scott K9MA
On 3/10/2021 2:19 AM, Don Kirk wrote:
> Hi Scott,
>
> Great point and I normally try and match up fluctuations when possible
> but I can’t be certain on this one as it did not fluctuate (it was on
> constant versus the easy find I had 2 days earlier). I will know
> pretty soon as the utility company in this area usually responds to
> our reported cases within a few days time (usually next day). The
> reason I actually wanted to track it down yesterday was because it had
> become so constantly on but that prevented matching up fluctuations.
> The only thing I can go on in this case is that we did wind up with
> final heading matching up closely with his 4 element HF beam at 112
> feet heading and also very little alternative sources between Dan’s
> house and the pole in question (lots of open farm land and only one
> other string of poles between Dan’s and the suspect pole which where
> on Dan’s road running North/South which were clean up on VHF). So you
> are absolutely correct that I’m jumping to conclusions about this one,
> and I will report back as soon as the utility company responds.
>
> But the real purpose of my posting was that this was the first case of
> power line RFI hunting I have done in which case ground based tracking
> on HF made absolutely no sense as the direction finding gear always
> appeared to point perpendicular to these specific lines regardless how
> much I walked the lines even though I made sure I was back away from
> the lines a great distance (typically 300 to 500 feet away from the
> lines) and this situation existed on 1.8 MHz as well as 24.9 MHz. If
> I went far enough North of these East/West lines I could hear and see
> on my SDR display similar noise coming from the NW direction but that
> did not match what Dan’s 4 element beam yielded which was NNE, and
> definitely no longer A North direction which is what the portable HF
> gear indicated when South of these lines (very confusing situation to
> say the least). It appeared if I was South of the lines I would
> always point North which was perpendicular to the lines and if I got a
> reasonable distance North of the lines I would point NW which
> definitely did not agree with Dans HF beam at 112 feet.
>
> Keeping my fingers crossed and getting the suspect pole fixed will
> hopefully clear up my direction finding confusion even if it’s not the
> source of Dan’s problem as it’s definitely polluting the East/West
> string of poles I mentioned.
>
> Thanks again for the comment and I was kind of expecting it from
> someone (including myself). I will provide update as soon as the
> utility company responds.
>
> 73,
> Don (wd8dsb)
>
>
> On Wed, Mar 10, 2021 at 12:07 AM K9MA <k9ma at sdellington.us
> <mailto:k9ma at sdellington.us>> wrote:
>
> I presume that you know that was the right source because the problem
> went away after it was fixed. However, you don't say how you knew you
> were tracking the right source earlier. I've also tracked a lot of
> power
> line RFI, and have found that this is a huge issue. You will hear
> many
> noise sources while walking or driving around, most of which are
> NOT the
> one causing you the problem. My solution is to simultaneously
> listen to
> the noise relayed from the receiver at home and the tracking
> receiver.
> There are almost always fluctuations in the noise. When they match, I
> know I have the right source.
>
> 73,
> Scott K9MA
>
>
>
> On 3/9/2021 6:27 PM, Don Kirk wrote:
> > Just thought I should share something that was a first for me
> when tracking
> > down power line RFI and man it was frustrating, and I have
> tracked down a
> > lot of powerline RFI.
> >
> > I noticed some weak RFI at Dans (KB9AX) on 160 meters earlier
> this year but
> > did not have time to track it down. Dan also complained about
> the RFI and
> > he mentioned this week that it was not strong but had become very
> > consistent. It definitely looked and sounded like powerline
> noise (120 Hz
> > spikes observed on audio scope and SDR receiver, etc.) Today I
> decided to
> > follow up on this RFI and using both my portable flag as well as
> a tuned
> > loop the direction indicated the noise was North from Dans QTH.
> I did some
> > tracking and both antennas kept pointing perpendicular to some
> power lines
> > a long distance North from Dans that were running East/West
> along a major
> > road and I was standing a good distance from the lines out in
> farm fields.
> > No matter where I walked my antennas kept indicating the signal
> was coming
> > from the lines with my antennas always pointing perpendicular
> to the lines
> > for peak signal even when I was hundreds of feet away from the
> lines (like
> > 500 feet or more away from the lines). Dans 4 square receive
> antenna
> > system (DX Engineering 4 square receive array) indicated the
> signal was
> > about equal when pointing NE and NW which pretty much agreed
> with the North
> > direction my portable flag and tuned loop indicated and the
> East/West power
> > lines are 0.75 miles North of his receive array. I started to
> get the
> > feeling that the ground wave signal from the pole generating the
> signal was
> > weaker than the signal propagating down the line in our
> direction, and
> > therefore I could not detect the RFI directly from the faulty
> pole with my
> > ground based antennas.
> >
> > We therefore looked for another frequency where the powerline
> RFI might be
> > heard from Dans, and using his horizontal HF beam (4 element
> beam up at 112
> > feet) we found the signal up on 24.9 MHz and it was strongest
> when pointing
> > NNE. Again my portable flag and tuned loop used on 24.9 MHz
> indicated the
> > signal was coming from the North (antennas perpendicular to the
> power
> > lines) when standing at Dans house very far from these lines
> (0.75 miles
> > from the lines). I then decided traditional direction finding
> was not
> > going to work. I then used my tuned loop adjusted for 24.9 MHz
> and with
> > receiver gain backed way down I drove the East/West lines with
> my small
> > tuned loop sticking out the window until I could hear the signal
> on 24.9
> > MHz. I then got out of my car and used my portable 4 element
> beam on 135
> > MHz and quickly found the faulty pole but the faulty pole was
> different
> > than all other poles I have located in the past from an RFI level
> > standpoint. I normally have to use 20 to 30 dB of attenuation
> with my 135
> > MHz receiver and 4 element portable beam to isolate a faulty
> pole, but I
> > actually was able to isolate the pole from nearby poles using no
> > attenuation at all but 10 dB of attenuation was ideal. This pole was
> > definitely generating RFI and I could even see low level of RFI
> coming from
> > it up on 437 MHz with a portable 4 element beam with SDR
> receiver, but it
> > was generating the weakest amount of RFI than I have ever
> encountered with
> > a power pole and I believe this is what caused traditional radio
> direction
> > finding to be useless (propagated signal along the lines was
> stronger than
> > the ground wave signal when viewed from Dans house). The faulty pole
> > turned out to be located 0.84 miles from Dan at a heading of 44
> degrees
> > which really is not very far compared with other faulty poles we
> have
> > encountered at his QTH and some have been double that distance while
> > generating much stronger RFI. When close to the pole (few
> hundred feet
> > away as an example) my traditional HF direction finding
> techniques using
> > both my portable flag as well as tuned loop worked great and pointed
> > directly at the faulty pole which I was happy to see but this
> sure had me
> > scratching my head as I spent many hours tracking down this
> faulty pole.
> >
> > I just wanted to share this experience as it was definitely
> frustrating,
> > but I'm glad I didn't give up. I suspect others may unknowingly
> run into a
> > similar situation but hopefully it will be few and far between.
> >
> > P.S. I had my easiest powerline RFI find just a few days ago at
> Kens (KJ9B)
> > and the utility company responded today and said the problem was
> a bad
> > insulator. You can see my youtube video of this find at
> > https://youtu.be/X_5h-gSc6Ns <https://youtu.be/X_5h-gSc6Ns>
> >
> > 73,
> > Don (wd8dsb)
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>
>
> --
> Scott K9MA
>
> k9ma at sdellington.us <mailto:k9ma at sdellington.us>
>
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--
Scott K9MA
k9ma at sdellington.us
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