I will be spending some time in MO and I notice that the State Police use duplex low band channels. Is there a freq I can punch in that I can hear both sides of the broadcast?
Unforunately no, you will need the frequencies for the car to dispatch and dispatch to car. You will also need to be relatively close to hear the troopers communicate with dispatch. Depending on the setup you have it will be anywhere from 10 miles(with an awesome mobile setup) or about a mile with a handheld scanner and rubber duck antenna.
You might also make certain that you have the local county dispatch frequencies programmed. I know that here in SW Missouri, a lot of troopers will deal with the county dispatch on their local freqs as well.
Don't forget to program the uhf frequencies as well. There is quite a bit of activity on the M.H.P. 460s. May make it easier to hear both sides of the conversation at times. Have a good trip!