The design of transmitter drives and receivers for single-sideband systems

Abstract

Many of the long-distance short-wave radio links between Great Britain and overseas countries are being converted from double-sideband (d.s.b.) to single-sideband (s.s.b.) operation because of the improved performance so obtained; this has necessitated new designs of s.s.b. generating equipment and radio receivers suitable for commercial operation. The type of s.s.b. transmission used incorporates two channels, each 6 kc/s wide, on either side of a reduced level pilot carrier which is nominally 26 db below the peak level of the sidebands. The function of the pilot carrier is to provide automatic gain-control (a.g.c.) and automatic frequency-control (a.f.c.) in the receiver.The equipment described includes:—(a) A drive equipment for generating a low-power two-channel reduced-carrier s.s.b. signal for subsequent amplification in the highpower stages of a radio transmitter.(b) A monitor receiver which is associated with the drive equipment and transmitter, and which enables either channel of the radio frequency (r.f.) signal at various stages in the transmitter to be demodulated to audio frequency (a.f.) for aural or electrical tests of quality and distortion.(c) Single-sideband receivers suitable for the reception of twochannel reduced-carrier transmissions, for use at the receiving station of a radio link. Receivers for single-aerial operation and triple-diversity spaced aerial operation are described.The performance requirements are stated, and the design, layout and performance of typical equipments are discussed.