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1-6 of 6 messages
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Diagnosing Power Line Noise
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by AA6CJ on October 13, 2009
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To all:
S5-7 noise level from 80-10m. Well, that's the big problem. I've tried eliminating power to my house and that didn't fix it, though I've found many little noise sources within the house...none are so big as to fix the main noise problem.
How can I determine for sure that its Power Line Noise? What is the procedure for isolating the noise, and how far away from my home should I be investigating?
Lastly, is there something I can buy that is effective against power line noise (like MFJ 1026 or ANC-4)?
73,
Fred
AA6CJ
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RE: Diagnosing Power Line Noise
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by WB5JEO on October 14, 2009
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It's likely not very far away. A common problem is a broken ground lead at a transformer. Another is simply a defective transformer. I had an intermittent problem once caused by build-up of lint from a nearby cotton gin. In high humidity, it would create a poorly conducting path to ground. Went away when it dried up and after a rain hard enough to wash it off. It was mostly seasonal at ginning time. The defective transformer was pretty easy to locate, since the beam clearly indicated direction. If there is only one transformer in the area, it's a good suspect. The trick is convincing the power company that it's there. It's not that they're opposed to fixing it. In fact, most will deal with it, because it suggests that the transformer may fail, and a broken ground lead is something they want to fix. Any sort of reasonably accurate direction finding or a clearly stronger signal on a portable when near the pole should be enough to get them to check. It helps if you can be there to demonstrate it for the tech. They may also have one or more means of testing for faults. Some analyze gasses generated in the transformer fluid. Others do other analysis on the fluid or work off features of the current. If the transformer serves only your house, they may even take it out of line to see if the noise stops. No processing is going to do much with that kind of noise, not in any way that you'd want to live with.
In an urban commercial environment, neon sign transformers may be offenders. They just have to be run down by D-F or the portable receiver. If anyone happens to have a well-designed HF receiving loop, it's a great help locating any of this sort of thing.
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RE: Diagnosing Power Line Noise
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by WX7G on October 14, 2009
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Shutting off the AC power to your house is the experiment that reveals that the noise is not conducted to you via the AC outlet. Line filters on your radio will not help.
You can look for the noise source using an AM radio.
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RE: Diagnosing Power Line Noise
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by WX7G on October 14, 2009
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Take a look a the eham reviews of the MFJ-1026. It appears to be quite effective.
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RE: Diagnosing Power Line Noise
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by AA4PB on October 14, 2009
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ARRL has a great book "AC POWER INTERFERENCE HANDBOOK" that can answer all your questions.
Most of the time the problem is caused by defective insulators and connections up on the poles.
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RE: Diagnosing Power Line Noise
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by W5DC on October 14, 2009
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One thing you can do to be a bit more sure that it's power line noise, although other line synced noises will still show this, is to put you ham receiver on am and look at the output on a spectrum analyzer of some sort. If you don't see a harmonic series of line frequency or 2x line frequency, then it's not power line or line synced. This can also be a good way to adjust noise blankers.
73, Dunc, W5DC
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