Hello Mike. The first clue is that the signal is moving up and down the 2 meter band. This would tell me that something not frequency controlled is causing the interference. Not frequency controlled would mean that the transmitter is not crystal or GPS locked to a specific frequency. Now, something that is frequency controlled may be involved with the IMD mix, but the signal that is free running is possibly causing an IMD mix to drift. I have seen this happen in a PA when it was NOT transmitting. We had a case of a paging transmitter PA that would go into self oscillation when it was not keyed by the exciter. The PA had power to it at all times and it would create interference when it was idle.
Some random thoughts: Your paging company signal may be mixing with it, but they may not be the culprit. 10AM can be busy time for a paging company, so the fact that it happens around that time would not be unusual. How do you know the data is from a specific paging company? Did you listen to their signal and the interference at the same time? Is it exactly the same? He says that he has remote control of the transmitters. What happens when he shuts them both off? As someone else pointed out, does he have a link frequency that he ties the sites together with? The link transmitter may be causing the interference, or be part of the RF mix. An IMD program will be useless to figure the IMD of a drifting transmitter that is part of a mix. You said 462.850 and 462.925 are also involved. What is on those frequencies? Who is on these frequencies and how are they involved? A lightning hit may have caused this all to happen. In my last job I troubleshooted lots of interference. You really need to take an antenna and directional find the source of the interference. It is time consuming, but will lead you to the physical source of the interference. Don't be fooled that it is positively the paging companies fault, as it may just be a mix in some other service PA. The last one I found was interference on a 53.85 Mhz repeater. At first, the culprit seemed to be the NOAA weather station on 162.55Mhz. NOAA weather audio was coming through the repeater crystal clear. It turned out to be a telemetry station PA that was mixing 4 X 53.85 - 162.55 = 52.85Mhz. The mix was exactly on the input! The telemetry station was owned by the water company that allowed us on the site, so we ended up moving the repeater to 53.71Mhz. We could have pushed the water company to fix their equipment, but probably would have been asked to leave the site. Sometimes diplomacy rules. I worked for paging companies for quite awhile and know that they get a bad rap, probably rightfully so for the most part. This sounds like the paging company is willing to work with you. My gut feeling is that you are going to find something else causing the problem. Again, diplomacy rules. 73, Joe, K1ike Mike wrote: > A couple of weeks ago, our repeater system started to experience interference > from a paging system. The repeater is on 146.850 (-600 KHz), with the > antenna system about 120 feet up a water tower. T
