Some developments in commercial point-to-point radiotelegraphy

Abstract

Developments in point-to-point radiotelegraphy have been concerned chiefly with the improvement of reliability to facilitate the introduction of time-division multiplex systems using direct-printing equipment, and to ensure continuous communication over difficult circuits such as those to the antipodes.Methods of reception using frequency-shift keying are discussed in relation to distortion, interference and multi-path effects; figures are given for the results of tests with this system compared with those of the on/off keying system. In one case, the lost capacity due to poor radio conditions was reduced by 39%.Radiotelegraph relays are described which cover interruption of direction communication, and charts are included to show the recovery of lost time. Owing to the introduction of radio relay stations at Barbados and Colombo, the periods when no communication is possible between this country and Australia have been reduced to negligible proportions. The effects of ionospheric disturbances on the London–Montreal route have also been greatly reduced by the use of radio relay stations at Ascension and Barbados; the station at Ascension has been in use since 1939.Equivalent phase modulation of short-wave transmitters is discussed or use with long-distance facsimile circuits.Concerning aerials, the development of horizontal-dipole receiving arrays to augment the vertical broadside-beam array, is dealt with; also a review of wideband coupling devices for coupling balanced aerials to coaxial feeders. Mention is made of the advantages of remotely controlled and unattended radio transmitters in reducing congestion on radio-station sites and in minimizing personnel.The paper also deals with telegraph printing systems; the doublecurrent cable-code system is described, and compared with 5-and 7-unit systems for undetectable errors and flexibility of operation.A frequency-modulated v.f. system for the control of radio stations is described.Finally, under the general heading of miscellaneous telegraph equipment, the paper contains a description of a high-speed photo-electric morse transmitter and an electronic keying device.