RFI at W9RE from electric fence.

Below is an audio analysis using Audacity software of the RFI popping noise that W9RE was experiencing that turned out to be from an electric fence 0.8 miles NE of his location. The pulses measure 1 milli-second or less in duration, and they occur approximately every 1.08 seconds. A recording of the audio can be heard on youtube at the following URL: http://www.youtube.com/watch?v=M99kyixyLnc&feature=youtu.be

Tracking Details

It was approximately 25 deg F today (Dec 8, 2016), and the recent drop in temperatures caused massive amounts of power line RFI which made direction finding using portable direction finding equipment almost useless. It was hard to detect nulls and peaks of the 1 hertz popping signal we (W9RE & WD8DSB) were tracking due to the power line noise in certain directions overriding the signal we were tracking. Therefore we had to resort to the more crude approach of driving around looking for peak signal strength of the 1 hertz popping noise.

The day before Mike (W9RE) tried driving around using his cars AM radio in his vehicle, but he was not able to hear the popping noise. Therefore today we used my car which has a very old AM radio (20 years old), and it does an excellent job hearing transient noise such as power line arcing (it apparently has little or no built in noise blanking circuitry). We were quickly able to locate an area where the popping noise was reasonably strong (approximately 0.8 miles from Mike's house), but when we got out on foot and tried using our portable DF equipment we were not able to get a good heading on either 160 or 80 meters (due to power line noise). We also tried using a portable 4 element Yagi with AM radio on 136 MHz at a distance of 0.1 miles from what turned out to be the eventual location of the RFI source and we did not detect the popping noise.

We then decided we needed to use an HF radio that could provide signal strength measurements (the popping noise was so short in duration that it did not register on the simple 5 digit LED signal strength meter that's on our DF receiver), so we put Mikes K3 in his vehicle using an 80 meter hustler antenna and set back out to the area where we had found the strongest sounding signal. We went outward from where the signal was the strongest to confirm that the S meter reading did indeed drop off as we moved outward from this location. We then went back and narrowed in where the signal was the strongest, and it was between a street in a residential neighborhood that backed up to a more rural property and the rural property itself, and a quick check with our DF gear tended to agree that the signal was in line with our current location in the residential neighborhood and the rural property.

We then decided to go to the rural property and knock on the door to ask permission to walk back onto their land toward the residential neighborhood. One of the younger members of the family gave us permission to walk back onto the property. We immediately noticed this rural property had an electric fence, and each time the electric fence discharged we could hear it on our portable DF radio and they were in sync. Don (WD8DSB) used a blade of grass to touch the electric fence, which allowed him to safely feel the discharge each time it happened. We tried clearing obvious brush that was touching the fence but had no luck eliminating the RFI (there were some areas of the fence we did not feel comfortable walking (from a privacy standpoint) and therefore we did not walk the entire fence line).

We then went back and talked with the adult homeowner, and after telling her our story she was convinced it was her fence causing the interference, and she even mentioned that there is an area of her electric fence where she can actually hear the fence discharge at a rate similar to what we described (she said it's not a problem with brush, but rather a problem of arcing between two wires on some kind of ribbon wire that's part of the system). She said she would definitely work on the fence, and she was extremely cooperative to say the least.

Later in the day Mike put his station back together, and noticed the 1 hertz popping noise which had been present for the past month is now gone (don't know if the home owner fixed the fence or turned it off).

Additional Details From Mike (W9RE)

Noise started about 1 month ago, periodic popping noise, at approximately 1 second intervals. I heard it on 160 and 80 (later determined it was basically from 1.4 MHz to 6 MHz) I pinned the direction to NE using my EFBS 8 direction 160 and 80 short vertical receiving arrays. I could detect it on my rotatable 80 meter yagi but it was not as loud on that antenna. On my 160 transmit antenna it was peaking at 30db over S9 albeit ambient band noise level was S9. I do not use AGC on CW and this was where it was the most noticeable. On LSB with AGC it was almost not noticeable, popping still there but the AGC took most of it out. It was almost like noise generated by flipping a 120VAC light switch if your radio would not dampen the spike down. I say this because on my 7800 with the NB off flipping a light switch cause a similar pop although the duration of the pop was not as long. So wide filters and no agc either on AM or CW made the popping stand out.

The area to my NE is a mixture of UG fed subdivisions and 10 acre homesteads (horses, chickens, etc). I drove the area yesterday (Dec 7, 2016) trying to see if I got close using my car radio turned to 1610 KHz if I could hear the noise but I could not. My car radio AGC masked the popping because I drove right past the source and did not hear it.

System we (W9RE and WD8DSB) used on Dec 8, 2016 in the car to track the signal down using S meter readings was a K3 with AGC turned off, RF at 12 o’clock, AF gain at 3 o’clock, AM mode and filter 4 kHz (wide). Antenna was a Hustler RM-75. Radio separate battery powered (SLA battery). S meter was sitting at about 10db over S9 (when we got close to the RFI the S meter would register 20 dB over S9 when the popping noise occurred).

Map below showing location of the Electric Fence relative to W9RE

(website created and maintained by Don Kirk (wd8dsb), December 8, 2016)