I've had these laying around here for a few years and thought I would take a peek inside. These are old crystal controlled business radios. I see a spot at the bottom of the radio for the second set of crystals. What do you have to do to set a second channel in these old radios ? There is a spot for tx and one for rx . What is the pairing for crystals ? The factory setting is 154.600 for one channel. Would I be correct in thinking that I need 4 total crystals for both radios ,all the same for another freq or two sets of two paired up for tx and rx? Thanks and please excuse my ignorance on these.