Using the "tried and true" AM radio trick (thx Cutty), I waved the radio around the controller and cables.
There was significant AM band noise (~530KHz) especially on the Ethernet cable.
I had a 7 ft. STP (Shielded Twisted Pair) CAT5 cable and decided to give it a try. I also placed 2 "low frequency ferrite" clamp-on filters near the controller box. (Intermark RFC-8MA)
This seemed to make a significant reduction as heard on the radio.
I was running 5x5x40 (1000) and 8x2x40 (640) gain with 240/200mV thresholds respectively. This would just keep it out of interference mode during "normal" times, not the Big Ugly Noise that I get from time to time.
With the STP for the Ethernet cable and 2x of the Intermark ferrites, I was able to set the gain to 8x5x40 (1600) with a threshold voltage of 220mV. It was actually not entering "interference mode" with 10x5x40 (2000) gain but the one amplifier was constantly incrementing the counts and it looked like it was on the verge of entering it.
I also tried wrapping the entire enclosure in aluminum foil, but it didn't seem like a worthwhile improvement for the detector performance. It did knock down the noise emanating from the STM Discovery board on the AM radio.
Update: A noise source returned and I had to lower the gain again.
Greg H.
