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RFI on 2 meters every ~300 kHz

Aug 5th 2014, 01:09


Joined: Nov 5th 2012, 10:56
Total Topics: 0
Total Posts: 0
I'm curious if anybody recognizes this "signature". I've had what sounded like digital intermod on certain 2 meter frequencies for almost two years. I've been more concerned with getting my power line noise fixed (they're down to the last 4 poles to fix) and in the process I found the location of my "intermod", which isn't.

I won't have a spectrum anlayzer until later this week, but just from my base station the noise appears to be about 30 kHz wide about every 300 kHz. Typical frequencies are 144.49, 144.85, 145.7, etc. I don't know yet how far above and below the 2 meter band the noise goes.

I've narrowed it down to about 3 poles and/or 3 houses. The source is about 900 ft from my base, no houses between me and it. It's definitely at that location and is NOT within my house (confirmed with radio taken to that location). On my horizontal beam at my house, the noise varies from about S5 to S9+20.

After a heavy rain we had, the noise went away for about a week. This noise runs 24/7 from what I've noticed.

The area is served by Time Warner Cable and AT&T U-Verse. I don't know of any other broadband provider. I didn't find any references to this type of noise from these providers. But that isn't conclusive either way in my book.

I've found nothing in the literature/forums about this type of noise at this frequency, especaially this strong.

Has anybody ran into a similar situation?

Aug 5th 2014, 22:57


Joined: Apr 4th 1998, 00:00
Total Topics: 0
Total Posts: 0
You'll have to employ some RDF (Radio Direction Finding) techniques to isolate the source as best you can to a single structure, tower, or pole. Document your efforts! Forget your preconceived notions as they will most likely be wrong (got that tee-shirt).

The quieting of the RFI after a rain leads me to think in terms of grounding. Moisture will enhance a ground rod's performance. Years back the transformer pole behind this house was generating a corona that was giving me problems on 2m packet and the local repeaters. I noticed the rain would quiet it for a few days so when it would act up during a summer dry spell I would run water next to the pole! The local electric cooperative did come out and I had to demonstrate the RFI as it was not bothering the AM broadcast radio in their truck which is what they used for their method of detection back then. A lineman did climb the pole and tighten and reposition the ground wire which helped a lot. My point is that it could well be something you won't think of although in your case I suspect some equipment with a faulty ground given the somewhat narrow spectrum the RFI occupies.

Good luck!

73, Nate

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