Application of Single-Sideband Technique to Frequency Shift Telegraph

Congestion of the 2 to 30 mc spectrum makes mandatory the reduction of bandwidths, on all types of transmissions, to the minimum technically required. This paper describes a method of economically utilizing the narrow-band plus high-stability techniques, normally associated with single-sideband systems, for frequency shift telegraph operation of one or more channels per transmitter. The frequency transposition type of fsk excitation is shown to have several advantages over present methods, whether for single channel operation with Class C transmitters or multichannel operation with linear transmitters. Tests made on a long-distance radio path indicate that frequency shifts as low as ± 30 cycles for single printer and ± 50 cycles for four-channel time-division multiplex are practicable, providing ultra-stable oscillators or afc is used.