A Stabilized Narrow-Band Frequency-Modulation System for Duplex Working

A system is described whereby the two terminals of a duplex radiotelephone channel are stabilized against each other by the use of standard automatic-frequency-control circuits and the common use of an oscillator for both transmitting oscillator and superheterodyne high-frequency oscillator. The send and receive frequencies are separated from each other by an interval which is the frequency of the intermediate-frequency channel. The system can be designed to give adequate frequency stability for most applications without the use of crystal control.