[RFI] Difficult power line RFI find.

[K9MA]

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
>
> 73,
> Don (wd8dsb)
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-- 
Scott  K9MA

k9ma at sdellington.us