POWER-LINE INTERFERENCE

As we all know, power lines are everywhere. Even in communities where power lines are laid underground, they are still above ground at some nearby location. Even with buried lines, transformer still abound in small bunkers dug into the ground and one of them may be right in front of your house. In addition, there are almost certainly street lights in your neighborhood that could also be a source of problems. And then we have traffic lights, internal home wiring just to mention a few other sources of potential power-line noise.

First you need to know that if, for example, your local power company has a problem near you that causes harmful interference, they are responsible for correcting it. They would clearly be in violation of FCC rules if they do not locate and correct the problem. From previous cases the FCC has gotten involved with a 30 day period to diagnose and repair seems acceptable to the FCC. The ARRL can also assist with these problems if it turns out the local power company is reluctant to diagnose and subsequently correct the problem.

Lower frequencies are more affected by power-line noise then VHF and above.  If you have a potential power-line noise problem in your area it will most likely be fairly localized. That is not to say that a problem many miles from you can not be heard at your location. It only means that if you have a high noise level on 160, 80 or 40 meters (and even higher) that the source is fairly close by. Now a true FM radio will not be affected by this type of noise source since noise in amplitude modulated and not frequency modulated. Some modern radios though have both an active AM and an active FM detector working all the time. This is easier to do (read lower cost) for the manufacturer then designing in switching circuits that are selectable. What this means is you might have a wideband receive FM handheld transceiver (HT) that hears the noise. Rest assured it is the AM detector hearing it, not the FM detector.

So what causes power-line noise? Weather exposure is a major cause of problems. Dirt can build up across an insulator and then along comes some rain. Now all of a sudden there is a small arc across the insulator and 40 meters has an S9 noise level. You call the power company, they send out a technician on a nice dry day and he finds nothing. But then you say that it has been quite for the last few days.  Sure enough, he leaves and a few days later along comes another rain storm and the noise is back. So if you pay attention to different conditions when the noise exists write them down and over time see if there is some correlation. If you have one of those nifty all mode, multiband handhelds (such as the Icom R-3), listen to the AM broadcast band in AM mode and start walking around the neighborhood. As you get closer to the source of the noise, it will get louder and stronger. You may even be able to pinpoint it to a specific power pole. Write down the power pole number from the power company label fastened to it.

Another common source of power-line noise is loose, cracked insulator or oxidized clamp, defective fuse and even a damaged lightning arrestor. These can all produce arcing across or within them that results in a very high HF noise level.

Not all power-line noise is limited to HF frequencies though this is where they are most common. It is rare to have power-line noise bother 2 meters or higher yet it does occur.  Think about it, power-lines are very long, transformers are big and even the high voltage insulators can be massive. These things tend to generate noise at lower frequencies.

If you experience this type of interference, do yourself and favor, and the power company one as well and try to isolate the source as close as possible. Write down as much information specific to the time and conditions of the noise as you can. Don't omit what may seem like an insignificant detail since that one small piece of the puzzle might potentially lead the power company technician to the actual source of the problem. But you do need to help yourself and go out and do some nosing around. Just NEVER, EVER, try climbing a power pole to get a "closer look." It is not worth the risk. Leave that to the professionals. If you can narrow the noise source down to something like that pole or behind that fence, let the power company take it from there. You also need to be aware of any potential tresspassing. The power company has right-of-way in all locations where they have equipment, you don't.

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