GB389917A - Improvements in or relating to apparatus for generating electric waves - Google Patents

Abstract

389,917. Valve circuits. GENERAL ELECTRIC CO., Ltd., Magnet House, Kingsway, London, and ESPLEY, D. C., c/o General Electric Co., Wembley, Middlesex. Dec. 3, 1931, No. 33510. [Class 40 (v).] In tone-frequency multiplex telegraphy, harmonics are extracted from a square, triangular or other wave-form comprising odd harmonics only, and their amplitudes are equalized by means of condensers or inductances. Thus from a fundamental of 60 #, signalling frequencies of 420, 540, 660 .., 2460 # may be obtained. In the arrangement shown, square waves, comprising harmonics whose amplitudes are inversely as their frequencies, are fed to a valve 13 from a commutator, a vibrating relay, a tuning-fork contact-breaker, or a photoelectric cell 11 intermittently illuminated through an interrupting disc 10 driven by a phonic motor 9 under the control of a tuning-fork 1. The condenser 16 and resistances 14, 17 are so proportioned that the harmonics applied to the grid of valve 18 are differentially attenuated so as to be of equal amplitude within the range required for signalling. The impedances 19, 20, 21 are so chosen that the signalling frequencies are amplified to substantially the same extent while lower frequencies are attenuated. The output of the system is passed to signalling channels such as 26, 27 containing keys 25 followed by filters 28, 30, and preceded, if desired, by filters such as 29. In a modification, Fig. 2 (not shown), the resistances 14, 19 are replaced by inductances so dimensioned as to produce the desired result. In a further modification a triangular wave-form may be applied to the input valve 13. The input amplitudes of the harmonics are then inversely proportional to the squares of their frequencies instead of to the first powers of these, and the output amplitudes are equalized by the use of two equalizing stages 14, 16, 17.