Abstract: A digital radio transceiver uses a differential 4-ary frequency shift keying (D4FSK) modulation scheme to achieve a radio that is low cost, miniaturizable, low in power consumption, and high in spectral efficiency. An adaptive digital "slicer" looks at a digitized FM video signal produced in the receiver to determine if the data sent is a 00, 01, 10 or 11. The digitized FM video signal is first processed by a differential decoder, the output of which is input to a peak detector. The peak detector outputs a signal upon the occurrence of a three-step transition, i.e., a peak-to-peak voltage value. Two-step and three-step transitions are separately detected and used to perform digital clock recovery. A carrier detect circuit uses a digital bit filter to produce a carrier detect signal that is reliable and glitch-free. The digital radio transceiver uses frequency hopping spread spectrum transmission.