Advances in Carrier Telegraph Transmission

N the comparatively short period which has elapsed since its commercial introduction in a practical form, the voice-frequency carrier method of operating telegraph has risen to a position of preeminence and is becoming the outstanding means for providing telegraph facilities over main toll routes. Since the original installation, improvements have been made in the carrier supply, level-compensating devices, maintenance facilities, and in numerous other specific physical parts of the system. Operating speeds have also gone up, and the number of telegraph channels per telephone circuit has been increased. Furthermore, this system, originally designed for cable circuits operating at voice frequencies, has been applied to open-wire lines and adapted by remodulation to o t h e r f r e q u e n c y ranges, i n p a r t i c u l a r t o t h o s e o c c u p i e d b y e x i s t i n g carrier-telephone systems. Some of the chief advances, however, have been of a more intangible nature, not the least of these being the clearer insight which experience and extended tests have given into the possibilities and limitations of carrier-telegraph systems with respect to interference and other causes of signal distortion. As a result of the success attained by the carrier-telegraph system for open-wire lines,1- 2 which had been in commercial service in the Bell System since 1918, this company's engineers turned their attention to the adaptation to cable circuits of the carrier method of transmission for telegraph purposes.