This is a continuation of the repeater interference issue we started to have last October. Maybe with a few new pieces of data, it'll spur some new thoughts.
Background: Last October, our repeater (146.850 MHz) started experiencing pager interference. The interference can be clearly heard on the input from various diverse locations around town. Most of the time, the interference seems to drift across the receiver passband (you can hear it coming and going as it drifts through), although this year it seems pretty much stuck in the repeater input (don't hear the drifting anymore). Last year, the interference was also heard on a couple of other area repeaters, 145.43 in Macon (15 or so air miles away) and 145.11 in Cochran (20 air miles away), so you can see that whatever this is covering a pretty large portion of the spectrum. I've also been told that it's been heard on public-service frequencies as well, although I don't know what those frequencies are (exactly) and have never witnessed it myself. Yesterday, the interference moved from the input of 146.85 to the input of 145.11 in a very rapid manner. a period of 5 minutes or so, and then reversed itself a couple of hours later. We know that the paging interference is coming from 462.775 MHz. The paging company owner is a ham and has been very helpful. The interference can come from any one of three different sites, one locally, one in Macon and one in Roberta (about 25 air miles away), all on the same frequency. He has set up a phone number that I can call and leave a voice page on the local system, which help us with the tracking immensely. I believe he's going to do the same for the other two systems. I've sat very near his system locally and heard NOTHING on the repeater input while the interference event is occurring. I've also checked all the likely mixing products as well as frequencies in his multiplier chain and heard nothing. We feel certain that it's got to be a mixing issue, (it's not likely he has three transmitters with the same garbage on the output) but given the way it behaves it's hard to locate the source. The large, rapid frequency excursions are a bit baffling. If you just consider 462.775 and 146.25, it puts you very near the audio carrier of CATV Channel 39, but seeing it move to the input of 145.11 and 145.43 puts the possible mix frequency somewhere between Channel 39 and Channel 40. The issue disappeared over the winter months. If it's a hot, sunny day you can be sure the problem will be present. A hot, cloudy day is also a fairly good bet. Also, a cooler, sunny day will bring it out. Cool and cloudy or cold and sunny do not allow the problem to manifest. The issue has been present during and after several days of rain, so that seems to eliminate the 'rusty bolt' syndrome. I tend to believe it's an amplifier mounted on a pole or tower someplace that's going spurious with heat, but that is just a theory. Beam headings tend to point to the paging transmitters rather than the possible mixing source, which is baffling me as well. I feel like I must be missing something obvious here, but all the back and forth ideas we've all been working on never seem to answer all of the questions. What do you guys think? 73, Mike WM4B
