Months ago in a topic I posted this:
The noise source in my area is centred on 156.4Mzh, and extends out, with two peaks - but there is nothing detectable on any narrow band radio - which in marine is of course still 25KHz - but even sweeping a 12.5KHz spaced radio from 156 to 156.8 reveal no detectable discrete channel usage of any kind, just an elevated noise floor - which of course conceals any weak normal transmissions at the lower end if the band. In addition, the noise seems to simply appear and remain, so is not linked to a normal TX/RX cycle that would come from a 2-way radio.
I was in my office today to get some orders out and turned on the analyser I use to keep and eye on marine band - and suddenly realised the hump of noise that starts at about 156.2 and goes up to 156.6 was missing - just a flat noise floor. As I came into the office the railway crossing barriers were down, the warning beepers going and there were some orange jacketed people - but I noticed I’d not heard any actual trains? I went out and wandered over - probably 50m or so, and spoke to the technical people. They’d had some issues with the crossing so yesterday night had removed all the technical kit in the small hut and replaced it. He asked when I noticed the interference had gone? I told him this morning. It was there on Friday but not today. They looked at each other - they were wondering if the random faults they’d been having for the past six months could have been also causing the interference. I guess we’ll never know, but with all the cabling going along - it’s not difficult to imagine the interference being distributed by the long cables - as my attempts to find the source with an RF explored had failed - the noise was just everywhere, but didn’t go up or down much?
I sort of feel I eventually found the source, but a dodgy rail crossing processor wasn’t my first thought!