Between the radio and the GPS receiver will be some system to monitor the radio receiver to decide whether it is safe to transmit or not, as well as take in the NEMA strings from the GPS receiver. In this case a TinyTraker3Plus also provides power to the GPS receiver. It's primary mission in life though is to convert the information it gets from the GPS receiver into an APRS packet, convert that into audo signals, and if it decides it is safe to transmit, does so according to whatever other rules are in place for doing so.