The digital nonsecure voice terminal (DNVT) is an alldigital four-wire telephone set used for noncryptographic communication over digital channels. It operates at 16 or 32 kbits/s. In this paper we describe the physical and electrical implementation of the telephone. The circuits are described to the block diagram level. The various states or phases of the signaling system, signal recognition codes, protocols, interfaces, etc., are discussed.

Shuttle voice processing uses a Variable Slope Delta Modulation scheme which is a variant of the ABATE algorithm. This paper summarizes the ground terminal subsystem which processes the multiplexed voice and telemetry data digital sequence in the downlink processing and digitizes the voice signal in the uplink processing. The Delta Modulation System (DMS) performance characteristics are given in terms of an intelligibility test score and in terms of time and frequency responses measured on a production system developed for NASA Goddard Space Flight Center. Implementation details of the encoder and decoder algorithms are given in terms of the circuit logic used to implement them.