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Powerline noise issue
10 November 2011 | by Despite the fact that I live pretty close to some power transmission lines as well as the regular above-ground residential service, I’ve been pretty lucky in that I’ve never had much of an issue with powerline noise. Unfortunately, that changed just about a week ago. It might be coincidence, but there there were about 4 or 5 houses around a block away from here that lost power due to the October snowstorm that didn’t get it back until last Friday, which is when I started getting S7-S9 powerline noise on all the HF bands, 2m, and, to a lesser extent, 70cm. Given that there were still others in the area without any power (we were very fortunate in that we never lost power at our house), I figured I’d wait until the local power company indicated that they’d finished restoring power to everyone before calling to report it. (Powerline QRN is bad, but it doesn’t come close to not having lights or heat.) In the meantime, I put my main HF rig (Icom 756 Pro II) on a battery and turned off the main breaker to the house to eliminate any possibility that it was something in the house, but with that done, there was no change to the noise signature.
On Wednesday, the QRN was gone for a few hours in the middle of the day, and I figured that maybe they’d found and fixed the problem on their own, but it was back by the afternoon. Yesterday, the power company officially announced that all customers were back in service, so I figured that I’d give them a call today to see what they’d say.
The automated voice response system had no way to understand “RFI” so it thought I was reporting an outage, and because that’s not the case, I finally got through to a human … who seemed equally baffled. I explained that I was an amateur radio operator and that I was hearing electrical noise that I hadn’t heard until about a week ago. He put me on hold for about 10 minutes and when he came out he said they’d be dispatching a crew.
While the recommendations for a situation like this are to try to narrow it down to a small area or even a single pole, in additional to not really having the right kind of DFing equipment for this, I’m home tending to one of my kids who is recovering from minor surgery, so I didn’t want to spend the time walking or driving around. I am crossing my fingers that PSE&G (my power company) will take this seriously enough to send out a properly equipped crew and find the problem. I’ll be keeping my fingers crossed.
Here’s a short video that I took showing what the powerline noise looks like:
5 Responses to “Powerline noise issue”
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I noticed in your video that most noise is on 20 meters and much less on 40 meters. Same here, except for the last few days: constant downpour which apparently short-circuits the noise, so I am enjoying a few days of noise-free operation. Good luck.
The total noise varies to some extent throughout the day, but it’s pretty constant. Last night we had some rain but I wasn’t able to listen to the radio at the time to see if that made a difference. But you are correct, there is nearly no noise at all on 40m.
Powerline noise often comes from a crack in one of several series connected isolators. The isolators work as a couple of series connected capacitors in vhich one of them has a spark gap that produces a spark each time the voltage goes above a limit. What we see is a pulse train with pulses that are close spaced as the voltage goes through zero because then the rate of change of the voltage across the spark gapo has its maximum. The pulse trains repeat at twice the mains frequency. In rainy weather there will be water in the crack so the voltage will never build up to high enough levels.
Powerline noise can be eliminated with smart noise blankers provided enough bandwidth is available. I write this comment because I am looking for wideband recordings made with SDR hardwares. Such recordings can be used to demonstrate how to fight the problem in software. Here are some examples, but they are not really bad enough:
http://www.sm5bsz.com/linuxdsp/blanker/leon2001/leon2001.htm
http://www.sm5bsz.com/linuxdsp/spur/autospur.htm
http://www.sm5bsz.com/blanker.htm
http://www.sm5bsz.com/pcdsp/pcblank.htm
In case anyone reading this has or can borrow SDR hardwares to make a recording of a really bad problem I would be very interested. I would want to use that recording as a better example of what is possible today. I would also want to use it to try to improve algorithms.
I am looking for recordings with bad powerline noise and with a strong signal that makes conventional blankers useless and with a weak signal that can not quite be copied. Preferrably near the strong signal. I am also interested in the loudspeaker output from the SDR software that goes with the hardware and particularly cases where
the strong signal is keyed for the weak signal to become copyable due to a noise blanker that works only when the strong signal is not present.
Find my E-mail at the bottom of this page:
http://sm5bsz.com
sm5bsc has it exactly right.
EMAIL your power company, and indicate it is interfering with tv and a.m. radio reception….
They will probably check with you to see if it is resolved periodically.
Remind them gently that they are responsible to alleviate this according to FCC regulations as you understand them.(be nice)
ALL power companies have a guy who can come out with a directional antenna at 135mhz a.m. or so and find the bad insulator from the ground.
good luck.
BTW, an A.M. portable radio with an internal antenna can help you locate the pole…just remember, it is DIRECTIONAL..
turn the radio, you can null it till you get too close….off the END of the antenna(internal rod is the best null.)
once you figure out the null, you should be able to walk toward the pole(s) and at least get close.