OK, you asked.
Had a police dept whose radio system would get knocked off regularly. Couldn't receive any mobile traffic that was more than a half mile away. In like 30 second spans, the mobiles were 'gone'. Then OK for a while, then bam, gone again. Well, put the receiver into carrier squelch mode, and there it was. Could hear a local paging transmission, quite distorted, along with something we couldn't recognize. Pulled out the spectrum analyzer and sure as s&&*^, there was an interfering signal. Further monitoring determined the second signal was coming from a transmitter we had no access to.
So, it's not the receiver, as the spectrum analyzer picked it up and had tried another receiver board. So it must be one of the transmitters. We changed out the paging TX with another and asked the other service to do the same to isolate the source.
Changing out both transmitters resulted in no change in the situation.
So we called in the experts. They ran tests on the transmitters, found no spurious transmissions, no intermodulation occurring, everything better than spec. (can't remember if they got clearance to do the same with the other transmitter) Any way, they also did some sniffing in the general area of the PD base station, saw the interference, but couldn't determine where it was coming from. They tried for a couple of days. Gave up. Said it could be anything from a rusty fire escape to ??? anything, but it WAS something in like an 8 block area.
Ended up moving the base station out of the area.
But they still had problems, mobile units in the area would now get 'deaf' from the interference as their transmitter was now about 4 miles removed.
Upgrading to multiple voting receivers, and 2 transmitters at remote sites pretty much took care of the problem.
Is that particular situation still there?? Most likely not, the paging transmitter is no longer located there. And the PD is migrated to 800Mhz trunking.
