SSB Receiving and Transmitting Equipment for Point-to-Point Service on HF Radio Circuits

The single-sideband receiving equipment, described in this paper, operates in the frequency range from 2.8 to 28 megacycles. The receiver provides for dual space-diversity reception of single sideband, independent sideband, double sideband, amplitude modulation, or phase modulation signals. The first heterodyne oscillator and the second heterodyne oscillator are common to both receiver circuits. The first heterodyne oscillator is a highly stabilized oscillator of the "captive" type. Diversified carrier from the two receivers is used in a comparator-type afc system. A noise-operated squelch disables the afc during poor-signal intervals. The agc voltage may be supplied from a choice of the signal carrier, the aggregate energy of either sideband, or (in the case of phone reception) from a combination of carrier and sideband energy. A diversity combiner is provided for the reception of phone signals. The telegraph diversity combiner uses a relatively simple limiter-combiner system. The receiver has a noise figure of 6 db and a minimum image ratio of 100 db. The companion transmitter is comprised of single-sideband modulating equipment, heterodyne frequency converters, and a linear amplifier system having a peak power output of 20 kw. The amplifier features continuous tuning throughout the operating range of 4 to 30 mc. The entire transmitter is designed to meet modem requirements of low distortion and low spurious radiation. It is intended to meet telephone, multichannel telegraph, and facsimile service requirements.