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Author Topic: Help identify periodic QRM  (Read 2130 times)
CHRISDX
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Posts: 244




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« on: November 20, 2012, 12:06:26 AM »

Hey, I have a new problem. Its an "AC buzz" type sound coming through. It starts about every 2 minutes and lasts almost exactly 23 seconds. It starts gradually (comes up over about 2 or 3 seconds) but stops suddenly.

I have a G5RV and hear this on several radios across HF (My Icom 7000 Noise Blanker clears it up).

As a test, while it was buzzing I turned off each circuit breaker one by one, to no avail.

Anyone had this isssue or know how I can hunt it down? The houses are close together here. I'm thinking a power line (transformer?) issue or some equipment in a house but no idea what, or how to track it down...

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KA4POL
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Posts: 1856




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« Reply #1 on: November 20, 2012, 01:23:27 AM »

That looks like some machine being switched on regularly for a constant period.
You already excluded your home. Does it occur 24/7 or can you see some daily pattern?
You need to use some direction finding equipment. An old AM radio would do fine.
May be it's time to get into the DIY business: http://www.handi-finder.com/
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CHRISDX
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Posts: 244




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« Reply #2 on: November 20, 2012, 09:58:38 AM »

Well I just got up (I work nights and listen on my nights off), and no there is no QRM at the moment that I can recieve.

Thanks for the DF tip, my handheld wasnt much help last night as I dont know ehere to point it, although it has a ferrite bar inside so I guess that means the null is off each end? (Degen 1103)

I hope I can find this!   Smiley
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KA4POL
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« Reply #3 on: November 20, 2012, 10:30:52 AM »

You need to find a pattern for this QRM. Just a sample, a photovoltaic array will not work during night times.
Yes, the null is where the ferrite rod ends point. So you either can use the maximum or the minimum to locate a direction. Try it outside, perhaps half a mile away, as well.
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K8AXW
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« Reply #4 on: November 20, 2012, 11:51:53 AM »

CHRISDX:  The symptoms you describe might possibly be a bad doorbell transformer.  I had the same problem several years ago. 

When a doorbell transformer goes bad, quite often they will arc inside the windings and the cycle is similar to what you describe.  Most of the time the doorbell will continue to operate as if there isn't a problem.

After shutting off the main breaker and finding I still had the problem I notified the power company.  They sent out a truck and crew and proceeded to cut power to each house that was fed from the same dropping transformer. 

When they found the house that had the problem, they notified the residents and mentioned that they had a bad doorbell transformer and suggested they get it replaced. 

Fortunately, they promptly did and all was once again peaceful in the valley.

Oh, I would play the "illegal interference card" only if necessary.  The will be smarting a bit from having their power abruptly cut and there isn't any point in agitating them more..... until later.
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WX7G
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« Reply #5 on: November 20, 2012, 12:15:34 PM »

It sounds like how someone described battery charger QRN (not QRM) he found.
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K5LXP
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« Reply #6 on: November 20, 2012, 01:43:55 PM »

Echo KA4POL, this same kind of noise was a bad streetlight a quarter mile from my QTH.  I DF'd it with a MW receiver that had a loopstick.  Got a few bearings, then went driving around and soon was able to pick it up on the car radio.  That got me within a block of it, from there I could see the streetlight blink on and off in sync with the noise.  A call to the local utility with the pole number and a few days later it was resolved.

Mark K5LXP
Albuquerque, NM
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N4NYY
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« Reply #7 on: November 20, 2012, 02:24:04 PM »

Chris,

You make need the help of a local radio club and foxhunt it down.
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CHRISDX
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Posts: 244




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« Reply #8 on: November 20, 2012, 03:56:33 PM »

OK it was not active during the day today, but now at 7pm I turned on the radio, and it's back. Interesting!
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K8AXW
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« Reply #9 on: November 20, 2012, 07:50:26 PM »

Off daytime - On nighttime......probably street light sensor.
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CHRISDX
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Posts: 244




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« Reply #10 on: November 20, 2012, 07:53:22 PM »

Found it.    We have no radio club nearby that I know of but my colleague at work KO1H is president of the semi-active RI wire antenna club and very active ham, and he suggested that street lights will cycle like that. BINGO.

I set my car AM radio to a nonstation and was driving around to establish a perimeter. I got the North-South done (about 2000' total span) and headed to the next street over and the house behind mine had a flickering street light on the pole. I parked under it and sure enough when it cycled the radio went crazy for about half a minute until it gave up trying to start.

Time to call the power company...

what a relief!
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KA4POL
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« Reply #11 on: November 20, 2012, 10:13:43 PM »

Good to hear that. By the way, some of these street lights do have photo cell switches which can be activated by a laser pointer...  Wink
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CHRISDX
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Posts: 244




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« Reply #12 on: November 20, 2012, 10:23:12 PM »

is there no way to edit my original post?  I wanted to add [SOLVED] to the title and cant do it...
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KA4POL
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« Reply #13 on: November 20, 2012, 10:26:28 PM »

I once made a typing mistake, no chance. The only way is through the moderator. Just leave it and it goes down into the archives.
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N4NYY
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« Reply #14 on: November 21, 2012, 04:47:17 AM »

Chris,

Put pressure on them. The FCC is usually pretty good against power companies, if they do not fix the problem.
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