316 BELL SYSTEM TECHNICAL JOURNAL 



open wire and coaxial carrier systems, from twenty-six to twenty- 

 eight of these modulators are needed in each direction for translating 

 each twelve-channel group of speech bands from voice to carrier and 

 back again. These copper oxide modulators have no power costs, 

 tube replacements or possibilities of power failures. In Fig. 1 the 

 four 3/16 inch diameter copper oxide discs generally used in a carrier 

 telephone modulator are shown individually, assembled with con- 

 nections, and potted in a can. 



The carrier terminals have tended to become increasingly complex 

 as it became their function to place more and more channels on a 

 single pair of wires. The extreme simplicity and reliability of copper 

 oxide modulators have been of great value in helping to overcome this 

 tendency. Copper oxide modulators have been used from zero fre- 



Fig. 1 — Four disc copper oxide modulator. 



quency to nearly four million cycles. Certain modulators for coaxial 

 carrier systems have been designed to modulate simultaneously as 

 many as sixty speech channels spaced over a 240,000-cycle band of 

 frequencies. 



Copper oxide modulators probably differ most from tube modulators 

 because the simplicity of the rectifier elements allows a much greater 

 variety of circuit arrangements to be used. Although the underlying 

 principles of operation are not new, it has become necessary to investi- 

 gate numerous transmission effects that could be neglected in tube 

 modulators. This has resulted not only from the newer circuit arrange- 

 ments with their smaller losses, but also from higher transmission 

 standards for the overall system along with the greatly increased 

 numbers of modulators in long circuits. Copper oxide modulators, 

 unlike tube modulators, transmit signals equally well in either direc- 

 tion. While this is a simplification in allowing a modulator also to 



