Abstract: A range tone system for determining the range between a satellite or spacecraft and a ground station FM modulates one of a 3968 Hz, 283 Hz or 35 Hz range tone onto a 27.77 Khz range tone. Modulation is accomplished by simultaneously addressing a plurality of PROMs by related clocks. The PROMs are preprogrammed with data representing the 27.77 KHz tone frequency-modulated by another range tone. Narrow-band filtering recovers the 27.77 KHz range tone from the received signal, and frequency demodulation coupled with narrowband filtering recovers the lower-frequency tone. The two recovered tones are processed simultaneously to provide both high resolution range information together with ambiguity resolution.