My bet is you are a victim of overload from FM Broadcast radio stations.
The system you are monitoring is a VHF system and the GRE type radios have no or very poor filtering of FM broadcast. Even stations 25 miles or further away can affect a GRE design. GRE designs are very well known for this design problem.
For starters, try cranking the squelch knob way up and see if the radio resumes scanning like it should.
Why the GRE designs still have the squelch circuit enabled for digital systems has always baffled me. A typical analog squelch circuit is not needed for digital systems.
You can also try turning the attenuator on while playing with the squelch control. I usually find the attenuator in the GRE designs to do more harm than good but if you are working with strong signals, it may help.
If the above seems to help, invest in an FM Broadcast Band Notch filter.
I can't speak for any but the one sold by PAR. PAR's FM filter does wonders. One other thing is VHF paging signals can also wreak havoc with a GRE design. I also must use both VHF paging band notch filters the PAR sells. One for the 152 and the 158 MHz bands.
My GRE's would be useless here without any of the above filters.
PAR's FM filter can be seen at:
VHF-FM Broadcast Filters | PAR Electronics | Filters for the commercial 2 way market, MATV, FM broadcast, laboratory, marine industry, amateur radio, scanner and short wave listening enthusiasts
And their various paging filters at:
PAR Electronics | Filters for the commercial 2 way market, MATV, FM broadcast, laboratory, marine industry, amateur radio, scanner and short wave listening enthusiasts
If the FM filter alone does not do the job, look at the two paging band filters for the 152 and 158 bands.
My bet it on FM broadcast though. Those stations often kick out 100 thousand watts and will destroy the front end in a GRE designed scanner.
And contrary to what some claim, the newer TRX 1 and 2 do not have improved front end filtering and are just as susceptible to overload from FM broadcast.
Overload from FM broadcast stations can wipe out reception on a GRE in both VHF bands and the UHF band. I've seen it also affect the 800 MHz band but that is rare, The UHF band is also not near as susceptible to overload from FM broadcast.
I also have high power UHF paging transmitters very near my location but they have never caused an overload problem with any of my tons od radios so I've ever needed a filter for those transmissions.
Depending on the GRE or Whistler model, the signal indicator may show a signal when there is none. Some will show full bars and some just show the S indicator. That is often an indicator the radio is being swamped by some signal not on the frequency tuned to or not even in the same band!
