VHF Interference

I have been lucky that I have had little so called "power line" interference in the years I have been in ham radio. As a little back ground all buzzing type of interference is assumed to be powerline related by most hams. The truth is most of the time it is a customer owned device and not power line hardware. I learned this when I worked for the power company. Some devices most lay people would never think could cause interference. This makes it difficult to explain to someone that their fish tank heater, doorbell transformer, or butter keeper is causing interference.

As a teenage ham I had my first experience with "power line" interference. I would get an intermittent buzz on HF from time to time. I never knew the power company would even look at such a problem but they will.....Sooner or latter.....Maybe never. But anyway, I never investigated the problem. It was not that bad so I lived with it. It would go away after a few hours and would not be heard for days or months on end. I found out latter that what I was hearing was not from the power lines but more likely from a doorbell transformer. In the 60's and it was common to put the transformer in the attic. A door bell transformer has a bi-metal strip that is a circuit breaker. When it get hot the strip will open up and cut the current. Unfortunately, on a hot summer day the temperature in the attic can get very high. The strip opens just a little. I suppose some corrosion on the contacts does not help the situation. You now get some arching. Add to this the power lines connected to the device and you have a nice HF antenna. These things will transmit a buzz for blocks.

Anyway lately I have heard a buzz on 2-meters SSB. It peaks when my antenna is pointed south. Until tonight the noise has not been too bad. Tonight it was almost S9 and wiped out the band.

I have an MFJ power line interference receiver I got at Hamvention a few years ago. I figured I would need it some day. This was the day. This little device is a simple VHF AM receiver with a simple dipole antenna. There is a null off the end of the dipole. The null is a nice way to "df" the noise. It is not fool proof because standing waves, houses, power lines, etc can fool you on the direction and intensity. With multiple observations from different locations you can identify the source if patient.

The MFJ receiver confirmed the southern direction. I walked south across the yard and got a peak in front of the house behind me. I walked 90-degrees to the null to see if I could confirm the direction. It still pointed south and not to either house behind me. I suspected the peak in the street was a standing wave or some other interference pattern but I was not near the actual source.

With this I installed my VHF loop antenna to the top of the van and listed on 144.200 in AM mode. I drove in the neighborhood behind me looking for a peak in noise. I would then get out of the van and use the MFJ receiver to determine direction. It was not long I found it: a nightguard light on a utility pole. There were three lights in the area. Two were in a park. I walked up to the ones in the park but the signal did not confirm I had found the problem. I then noticed the third lamp behind houses next to the park. I realized this was the light I DF'ed on the other street. I did not want to walk in someone's backyard so I stayed in the street. Near the lamp I was too close and could not get a direction on the noise. Walking a 100 feet down the street I could get a good direction off of the null. The direction was confirmed on both sides of the lamp. I am sure I have found the problem. I need to confirm this by being there at sunrise and see if the noise goes away when the light goes off. These lights are installed and serviced by the utility company. I don't know how eager DP&L will be in fixing the problem. I will do more monitoring of the situation to make sure I am right before contacting them. I will use this form to document the results of my observations.

So for tonight:

1. Noise heard: After dark, continuous with some variation. Monitored between 20:00 and 22:00. Did not listen outside of this time frame.
2. Weather: clear, dry, temperature 55-degrees, no wind
3. Noise level peak at home on FT-817, AM, antenna 220 degrees: S8
4. Peak noise on Tyronda Street on mobile FT-100D, halo antenna, AM mode: S5/6
5. Level on MFJ in front of driveway at 5524 Tyronda: 80