[Phlogiston]

I was messing with things last night and found that if I plugged my transmitter into a different outlet (different circuit) that the hum was a lot less. This is with all breakers on. If I plugged it back into the bench outlet, the hum was louder. I also found when I touched the plug from my CD player to the input jack, the hum increases. It used a 5v USB charger. I thought it may be the problem, so I plugged back into the bench, unplugged the charger and the hum is still louder regardless of the charger. So, whatever is on that line will come in on either the transmitter line or the CD charger line (same circuit). So, I have some hunting to do. In thinking back, this is the same circuit that my brother would have used back years ago for his ham equipment. Huh … I also experimented with intentionally laying the antenna right next to the extension cord to the transmitter with no change. Ed, now that you mention it, I do have hum issues in certain areas of the AM dial, which come and go. I have found our TV interferes, and our refrigerator (of all things) also puts out some kind of weird interference.

The TV has a switching power supply and the fridg might have an inverter. They want to run the compressors on HVAC at 400hz rather than 60 for efficiency OR, like on my well pump, they run the motor at a variable rate. Any of these switching devices might cause some RF interference - though on the 3 devices that I have, I have not noticed any. The switching supply on the laptop on my bench is another story altogether. It generates interference at a high level on the broadcast band and what looks like "dead" carriers on VHF.