All data comes through the control channel and your scanner decodes it. You can put more than one control channel in one system. When you are out of range from one it will pick up the next one in the list. When your scanner is set up for conventional it has no idea what to do with control channel data, only when setup correctly will it decode properly. There is many frequencies they might use on the system for voice but if your scanner has control channel only mode these are not neccesary.