A Long Range Digital Communicaton System

With the arrival of digital data-processing techniques, it becomes necessary both to increase the speed of communication between the data-processing and automatic control equipments and to increase the reliability with which the data are transmittedparticularly over comparatively long ranges. With the immense number of systems that must be developed to provide the everincreasing amount of data processing required by modern technology and modern business, a reliable digital data transmission technique for use over long ranges becomes critically important. This paper describes a high-frequency, digital data communication system using the quantized frequency-modulation (QFM) technique and the quantized phase-modulation (QPM) technique. QFM is a synchronous frequency shifting technique that can provide a predetermined amount of gap protection between successively transmitted pulses on the same subchannel frequency. The combination of these two techniques (defined below) provides a system with the capability of combating propagation anomalies found in the HF spectrum. The design of the system provides for a basic bit rate of 1000 bits/sec and is capable of expansion to 8000 bits/sec. System peripheral equipments provide digital inputs from facsimile and voice (Vocoder), as well as from multispeed teletype. Highly miniaturized modular construction is used throughout for all equipments and installations.