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Author Topic: Close by switching p/s RFI difficult to pinpoint source  (Read 1340 times)
W2MV
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Posts: 233




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« on: June 26, 2017, 04:28:46 PM »

I walked around the neighborhood with a portable receiver and a National RF HFDF in order to locate the source of switching power supply RFI on 40 meters, which occurs in clusters about every 55 KHz (and lower amplitude in between.)

I can get a deep null rotating the loop. The problem is that if I walk to another spot say 20,30, or 50 feet away the null is now pointing to a different source. Sometimes I get a deep null where the RFI appears to be emanating from a house, but then if I walk several tens of feet the null then appears to be coming from someplace else such as a power pole or my neighbor's pool pump. Driving me crazy. Ambiguous multiple directions for the source location. The RFI  seems to be "all over the place" which it very well may be, being conducted along the power lines.

Any suggestions how to better determine the "real" source?

Thanks
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KC2MMI
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Posts: 802




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« Reply #1 on: June 26, 2017, 06:11:34 PM »

Is this suburbia where you can circle around street lamps to check them out? Or cable company drops to houses?
What's the layout there?

If you were in Manhattan it could just be multipath and impossible to resolve.
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W2MV
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Posts: 233




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« Reply #2 on: June 26, 2017, 06:38:42 PM »

Yes, suburbia. LED street lamps, which I believe is what's causing RFI on 15 M at night/different source.

And yes, cable drops, secondary Con Edison drops, etc. The RFI in question disappeared for about 4 days but came back Sad
Thought I might have lucked out. It was REALLY quiet on all bands for those 4 days.
There's also something on 14 MHz...a carrier surrounded by some junk, relatively narrowband which comes on around dawn and shuts off in the evening...hours after sunset. The main offender is the 40 meter /switching p/s noise.
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NK7Z
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« Reply #3 on: June 26, 2017, 07:53:33 PM »

Print out your area using Google Maps...  Then take 10 or 15 bearings on the RFI, and lay them out on the map you pointed out.  You should probably see a preponderance of crossings at the source.  If you do not, widen your base lines.  I have a series of blog comments at:

http://nk7z.net/category/info/rfi-mitigation/

If you review these there may be some info that may help you locate your source...
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Thanks,
Dave
For reviews and setups see: http://www.nk7z.net
KH6AQ
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Posts: 7520




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« Reply #4 on: June 27, 2017, 08:20:58 AM »

The RFI source, or "transmitter," may be in one house but its "antenna" my be all of the power drops common to the mains transformer it is powered off. If so, it will defy DFing.
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NK7Z
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« Reply #5 on: June 27, 2017, 08:33:58 AM »

I have had luck locating sources like that by doing a drive around, on all cross streets in my area, and recording the S meter values.  You will see a peak when you are close to the source.  Once in that area, use a VHF/UHF receiver in AM mode, and a three or so element beam.

See:

http://nk7z.net/i-have-rfi-now-what-locating-it/

for more information that may help...

Look particularly at the map at:

http://nk7z.net/wp-content/uploads/2015/12/Overview-of-RFI-083012-40-Meters1.jpg

The RFI was found in the red area...
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Thanks,
Dave
For reviews and setups see: http://www.nk7z.net
N8EKT
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Posts: 565




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« Reply #6 on: June 27, 2017, 03:42:21 PM »

Canvas the neighborhood for someone using an invisible pet fence
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N3QE
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Posts: 4669




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« Reply #7 on: June 28, 2017, 06:49:32 PM »

I walked around the neighborhood with a portable receiver and a National RF HFDF in order to locate the source of switching power supply RFI on 40 meters, which occurs in clusters about every 55 KHz (and lower amplitude in between.)

I can get a deep null rotating the loop. The problem is that if I walk to another spot say 20,30, or 50 feet away the null is now pointing to a different source. Sometimes I get a deep null where the RFI appears to be emanating from a house, but then if I walk several tens of feet the null then appears to be coming from someplace else such as a power pole or my neighbor's pool pump. Driving me crazy. Ambiguous multiple directions for the source location. The RFI  seems to be "all over the place" which it very well may be, being conducted along the power lines.

Can you walk along the power lines, listening with a receiver without a directional antenna? If the RFI disappears every half wavelength (every 20M for a 40M buzz) then you're hearing RFI conducted from its source via the power lines. This is a very common situation, that the source itself doesn't do much radiating, but the power lines do, and the directional antenna like you found is near useless because all you're doing is nulling out the complex pattern from the many hundreds of wavelength long power-line antenna.
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