I've found over the years that the main culprit is usually FM broadcast radio stations for most users.
They don't need to be close either figuring many stations emit 100,000 watts of power.
Then the number two offender is paging transmitters in the VHF hi band (150 MHz) area. Paging junk runs a few hundred watts ERP usually and some run a near 100% duty cycle so they are rarely off the air. Paging is also wideband and then some if you look at the signals from some of those transmitters with a service monitor.
Both the above signal sources can and often do desense the heck out of GRE designed radios. Remember that GRE designed radios were sold under the GRE name, the RadioShack name and now the Whistler name.
They all use the same basic front end design including those sold by Whistler. The WS-1095 is really nothing more than a GRE PSR-800.
I've also experienced desense from a county PD precinct transmitter that is only a mile or two away from me. That one was not that bad though as they don't talk constantly
I've personally not had many problems from other strong signals in other bands.
Some speculate that the GRE radios have no or poor filtering in the VHF Hi band.
I actually think this may be true from some of the testing I've done.
I've not had much trouble from other high power stations like TV for example but VHF Hi and FM broadcast get in and can wipe out all bands in the GRE design.
We had a 5KW highway patrol transmitter on 42 MHz that was on the air very often. I live only a mile or two away. That transmitter never caused any noticeable desense in any of my GRE radios in any band. I also have 21 or 27 cell towers within a mile or less of my location and those never caused any issues. Some of those cell towers were really the old Nextel iDen network on the towers. Those signals also never caused me any real issues though.
So basically, almost all the crud getting in and desensing the GRE front ends is originating from signals between about 80 MHz up to about 160 MHz.
I first built stub filters for the FM Broadcast band. They helped but I was still being hit by something else. I watched the bands with a spectrum analyzer and found my desense occurred mostly when the paging transmitters in either the 152 MHz or 158 MHz paging bands went live on the air.
I built stub filters for those bands and my problem was mostly gone.
Stub filters are pretty wideband though so they knocked out signals that I wanted.
The stub filters were just a test that helped me ID the culprit(s) at nearly zero cost. Due to the wide notch width of a stub filter, I replaced them all with notch filters from PAR Electronics when I had all the offenders figured out.
PAR filters have a narrow notch width (a tight skirt) so you don't lose much above and below the filters center frequency.
I also messed with the old FM Traps that RadioShack sold but found many of them were centered way out of the actual FM band. They were a cheap way to test though as you could return them. I took the back off of many of those RadioShack traps and realigned them so they were centered in the middle of the FM Broadcast band. It was easy and usually just required opening or closing the spacing of some of the air wound coils.
A little hot glue fixed them so they would not go off frequency if they were dropped.
I later purchased a PAR FM Trap even though my main culprits were paging transmitters in the 152 MHz paging band and to a lesser extent, the 158 MHz paging band.
NOAA WX transmitters are also suspect for many. They run 24x7 and often emit 1,000 watts. I did purchase a 162 MHz notch filter from PAR but I mainly used it to get rid of the mixing products that affected my old crystal scanners and any radio that did not have triple conversion IF stages.
Lookup "stub filters" and you will see how easy they are to build. They can help you determine the culprits causing desense or intermodulation issues in GRE designed radio's or any radio made before they came out with triple conversion designs.
I don't recommend leaving a stub filter in place as they also have multiple harmonics and may be killing signals that you want.
Figure out the culprits and then purchase quality notch filters such as those sold by PAR.
The correct filter(s) can make a useless scanner work fantastic.
My nearest FM Broadcast station is at least 10+ miles away from me but it still wiped out the front end in my GRE radios or caused intermodulation distortion from mixing with other transmitters as they came and went on/off the air. The PAR FM filter took care of those problems easily.
All in all, the GRE designed front ends work well if given proper filtering at the antenna input.
I am curious if Whistler will improve things in this area if they ever produce a radio of their own design.
All in all, those that have desense or overload issues with a GRE design can usually fix the problem.
One thing to keep in mind, especially for those that live in high RF level areas, is that your problem is very likely caused by more than one source. So multiple filters are often needed.
The majority of 1095 user I have talked too on the side are external antenna users and none have mentioned overload front end issues. Also Doug (K4DPS) is using a serious external antenna setup and his 1095 is performing like a champ and pulling in some nice signals.
