SINGLE-SIDEBAND TRANSCEIVER DESIGN.

An investigation of underground radio communication showed the need for a transceiver operating at around 1 MHz and with an r. f. power capablility of 1 w. The requirements of such a transceiver are considered and certain circuit details discussed. For underground use, a suppressed carrier modulation system must be used to obtain maximum usable transmitter power, and a double-sideband suppressed carrier transmitter is simple to design, adjust and manufacture. Reception of d. s. b. s. c. signals with fairly simple detectors, however, presents a problem. Use of a single sideband, on the other hand, does not require such complication in the receiver but does require a more complex transmitter. Of three commonly used s. s. b. generation systems, only the filter method does not require careful circuit adjustment. Because filter-type s. s. b. generators are expensive it was necessary to examine other possibilities, particularly in view of the environment. The transceiver was required for operation in deep gold mines, shielded from surface noise by a mass of rock impervious to electromagnetic propagation. There is no channel congestion in this environment, and this makes it possible to accept transmitter characteristics which would be non-ideal elsewhere. Most important of these is the generation of an s. s. b. signal by the filter method which is of sufficient quality to simplify the receiving circuitry, but does not require excessive rejection of the unwanted sideband. Acceptance of this immediately simplifies the requirements of the sideband filter.