I started getting some chatter on the GSP's mobile extender frequency. I slowed down and then saw the officer. The speaker on my camera sucks, so you might want to turn up your volume. This is pretty normal range with the stock antenna you usually get about a mile. And you don't have to even be able to make out what they are saying for this to be useful, any static or voices on this channel means they are close.
YouTube - GSP Mobile Extender Example