I was using my little handheld transceiver, an ICOM IC-91AD, to talk on one of the local repeaters and I started getting some odd noise that was starting to annoy the hell out of me. I was only able to use the radio in my office; anywhere else in the house had the noise problem.
After a while of this I started getting more annoyed.
Let’s go over some data points first:
- I was getting interference on the W8OKE repeater on 147.015
- More generally, it was using the FM mode on the 2m band (144-148mHz)
- Sometimes the noise would “move” around on the band
- The noise was only happening around my house
- Sometimes it was worse than other times
- The FM detect was always on when the noise was happening
Going by the book (quite literally, the ARRL book) we started to walk around the house to see if any part of the house was any worse than any other part. The answer was a disappointing “not really.” The next step is to go down to the breaker box and start switching off breakers to see when the problem goes away.
One by one I started to flip the breakers while Ennie listened to the noise. Eventually we narrowed it down to one one circuit. It’s the circuit I had hung the TED-5000 off of. That’s the problem, right?
The backstory behind the TED is that it’s a device to monitor the overall electrical usage of my house. It has two current-sense loops that clip on the main feed into the house and a couple of small leads to get power from both hot sides. The way the box communicates to the outside is by injecting a bit of data on the 0V crossing of the power. (It’s very similar to how X-10 does things) The data “noise” is then received by another box outside the breaker panel and that then talks ethernet to the rest of the house.
Now that bit of noise on the power line was my first guess at the cause. The power lines are an unshielded, unbalanced system that would act like an antenna for this. Problem solved. Right?
Nope. Even after unwiring the TED I still get noise.
Unplug it and the noise goes away.
Maybe it’s an old power supply and something went awry in it. I have a spare from an older shaver. Switching power supplies (which this thing is) use high frequency switching to convert the input 120V to the required 12V. If something died there it’s conceivable that it could radiate some noise.
Swap and the noise went away.
For a few minutes. Damn.
Then I noticed that the shaver was in a test mode and a blue LED was pulsing in sync with the noise. Ah-ha!
It’s the shaver itself!
Now I just charge it and unplug it. No more problems. Though I wouldn’t mind getting a newer one that I don’t have to babysit.
You can listen to the noise on the video below: