GB384747A - Improvements in or relating to electric telecommunication systems - Google Patents

Abstract

384,747. Superposed telephony and telegraphy. LIGNES TELEGRAPHIQUES ET TELEPHONIQUES, 26, Rue de la PÚpiniÞre, Paris. Oct. 20, 1931, No. 29138. Convention date, Nov. 8, 1930. [Class 40 (iv).] In a two-way circuit balanced for frequencies used in telephony, fi 1 t e r s and/or amplifiers are provided passing a different frequency band in each direction, the different bands having a common band used for telephony and individual bands each used for another unidirectional communication. The circuit extending from A to B is balanced by networks 3. Signals in the direction A, B pass through network 5 and amplifier 1, which pass a frequency band of 300-3000 cycles per second, whilst signals from B to A are limited to the frequency band 100-2200 cycles per second by network 4 and amplifier 2. The band 300-2200 cycles is used for telephony, the system being balanced for this frequency range. Telegraphic signals pass from A to B using the frequency band 2200-3000 cycles whilst the band 100-300 cycles serves for telegraphic transmission from B to A. If telegraphic transmission from A to B only is required, a single network 4 with a cut-off at 2200 cycles is necessary, the band 2200-3000 cycles being used for the telegraphic transmission. The networks 4, 5 may be filters or resonant circuits tuned to the mean frequency to be passed, or the input transformers to the amplifiers may be arranged to provide the necessary frequency cut-off, in which case the filters are not provided. Although, as described, the two transmissions are telephony and telegraphy, either or both may be replaced by any other similar transmission.