A Frequency-Differential Phase-Shift Keyed Digital Data Modem for Operation at 4800, 2400 1200, and 600 Bits Per Second over Long-Range HF Paths

摘要

The ANDEFT/SC-320 is a variable rate (4800, 2400, 1200 or 600 bits/second) digital data modem prototype specifically designed for reliable communication over long-range high-frequency radio circuits. This modem employs such advanced and proven techniques as frequency-differential phase-shift keying, correlation detection, extended symbol length, guard time, segmented AGC, and dual-mode precision synchronization to combat HF anomalies such as multipath delay spread, frequency selective fading, high intensity atmospheric noise and man-made interference. The modem has provision for dual signal source diversity operation to capitalize on available space, frequency, or polarization diversity facilities, and in addition, can be operated with in-band frequency diversity. The prototype is built in two separate cabinets (modulator and demodulator) to enable field testing and to allow for easy expansion to an ultimate data capacity of 9600 bits/second. This report presents the principles of operation of the modem and the results of tests to determine the back-to-back performance in additive white Gaussian noise. (Author)