Copper Oxide Modulators in Carrier Telephone Systems

A T least as early as 1927, copper oxide rectifiers were being tried as ·L modulators for the speech channels of carrier telephone systems In this country. At this time only a rather large type of rectifier was available, better adapted for power use rather than in modulating the few milliwatts of a speech signal. Largely because of instabilities these early units were found to be unsatisfactory for modulator use. Further developments in copper oxide rectifiers made in various laboratories extended the variety and improved the quality of the product available, so that by about 1931 they began to be promising as serious competitors for vacuum tubes in modulators. Since 1931 continued improvements in copper oxide rectifiers have rapidly increased their field of application until now they are employed in practically all modulators of the latest types of carrier telephone systems. In the new systems a copper oxide modulator is used instead of the previous push-pull arrangement of two vacuum tubes. In cable,1 * Presented at W i n t e r Convention of A . I . E . E . , New Y o r k , N. Y . , J a n u a r y 23-27, 1939. 1 The general features of carrier telephone terminals have been described in a paper " C a b l e Carrier Telephone T e r m i n a l s " b y R . W . Chesnut, L . M . Ilgenfritz and A. Kenner, Electrical Engineering, J a n u a r y 1938. 315