I know they are generally known for cheap crap, but I've been using an old NADY 201 true diversity system on and off for over 20 years. It doesn't pick up police radio calls, or air traffic controllers, etc. It doesn't seem to change my tone, and it has always worked. I know there are much better systems out there, but this old NADY has never given me any problems and you can find them on Ebay quite often for relatively little $. YMMV.
Bill, tgo