GB149858A - Improvements in electric signalling systems, especially applicable to combined telegraph and telephone systems - Google Patents

Abstract

149,858. Western Electric Co., (Western Electric Co.). Oct. 3, 1919. Simultaneous telegraphy and telephony; repeating and amplifying systems.-On a line used for simultaneous telegraphy and telephony, a single amplifying-set is designed to repeat both classes of signal. This involves the use of transformers capable of dealing with widely different frequencies, and generally two separate transformers are used for the telegraphic and telephonic currents. Associated with the transformers on the input side of the repeater are devices for attenuating low frequencies more than high, so as to compensate for the opposite ettect which occurs in the line, thereby equalizing the total attenuation for all frequencies. The amplifying-set is also suitable for repeating intermediate frequencies, such as the current of 133 cycles sometimes used for telephone calls. In the one-way repeater shown in Fig. 1, the input side of the thermionic amplifier 16 is connected to line 1 through transformers 3, 4 designed respectively for telephone and telegraph currents, and its output side is connected to line 2 through corresponding transformers 17, 18. The windings of the telephone transformers are halved and the telegraph transformers are connected between them, or vice versa, and the telegraph windings are shunted by condensers through which the telephone currents pass. A composite circuit 7 between the two halves of the primary of the transformer 3 equalizes the attenuation of the different frequencies of the telephone currents, and a circuit 8 in the primary of the transformer 4 does the same for the different frequencies (of a lower order) of which the telegraph currents may be supposed to consist, or the equalizing-circuits 7, 8 may both be in series with the primaries of both transformers. Direct current can pass from line 1 to line 2 through impedances 21. Circuits are described in which the same principles are applied to a twoway repeater.