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Author Topic: Need help identifying RFI source  (Read 1928 times)
K2MK
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Posts: 467




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« on: July 03, 2007, 05:08:41 AM »

I have this recurring noise on my home FM radios and to a lesser extent on AM and TV. I don't hear it on the ham bands. I can easily live with it but I suppose my neighbors have it too and when I put up a more noticeable antenna in the next few months I don't want to get blamed for the noise. If it can't be eliminated I at least want to be able to tell them where the noise is actually coming from.

It can be heard here:
http://mhkravitz.googlepages.com/home

It's interesting in that it usually occurs around 8:30 PM and 6:30 AM. It does occur at other times as well and it also skips some days completely. There is always one burst of noise followed about 4 seconds later by a second burst. The noise always has the same pattern.

I heard it in my previous home for about the last 10 years and it followed me to my new home which is in the same town about 4 miles away.

The recording is of a local FM station at 101.1 MHz.

Any help identifying the noise source would be appreciated.
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WW5AA
Member

Posts: 2086




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« Reply #1 on: July 03, 2007, 07:49:18 AM »

Mike,

You may want to listen to the BPL files on ARRL's web sight. Hate to even mention it, but it sure sounds like broadband over power lines noise. I would also check with your power provider and see if they are running a test operation.

73, de Lindy
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WB2WIK
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Posts: 21757




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« Reply #2 on: July 03, 2007, 01:36:17 PM »

If it's been around for ten years, it can't be BPL, since that's only been deployed very recently.

If the noise "followed you," it's very likely you are generating that noise with something in your own home.  Most noise interference, other than that caused by lightning or the sun, can't propagate 4 miles.  Most of it won't propagate much more than 4 blocks.

I'd listen on a battery powered radio or TV and pull the MAIN circuit breaker to my home, completely disconnecting everything in the house from AC power.  See if that makes the noise go away.  If so, you're generating the noise, yourself and the next job is to find out which circuit the noise generator is on.  You can do that by turning OFF all the circuit breakers in the house, turn the MAINS back "on," and then turn on circuit breakers, one by one, until the noise occurs.

Now you'll know it's something on that circuit, so you can go look for what it is.

WB2WIK/6

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AA4PB
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Posts: 14384




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« Reply #3 on: July 03, 2007, 06:05:35 PM »

It sounds like a digital cell phone registering with the tower.
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Bob  AA4PB
Garrisonville, VA
K2MK
Member

Posts: 467




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« Reply #4 on: July 04, 2007, 03:40:13 AM »

AA4PB:

Bingo. You solved the mystery of the ages. The radio that always responded the most is on a night table right next to the cell phone charger. My wife charges her cell phone at about 8PM and removes it about 7AM. She doesn't plug it in every night. She's had this same phone for many years. Probably not 10 years but I was only guessing at that figure.

To prove the point. I turned off her cell phone and then turned it back on. As soon as it powered up the noise was heard on the radio. Obviously it was letting the tower know that it was alive.

Thanks again to everyone for their help.  Mystery solved.

73,
Mike K2MK
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WW5AA
Member

Posts: 2086




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« Reply #5 on: July 04, 2007, 06:25:19 AM »

Sorry Steve, BPL has been around for over 20 years! The systems are used in homes and businesses all over the world. Most people think of them as the plug-in to run DSL to a room that does not have a phone line. We have a large hotel in town that has runs its own BPL system to rooms and to monitor utility use for over 15 years. I replaced the one I was using with a hard line several years ago because it created HF noise just like K2MK's file.

73, de Lindy
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