GB776971A - Improvements in or relating to telephone systems - Google Patents

Abstract

776,971. Exchange systems. AUTOMATIC TELEPHONE & ELECTRIC CO., Ltd. Sept. 14, 1954 [Nov. 20, 1953], No. 32180/53. Class 40 (4). [Also in Group XL (b)] Waveguides are used for transmission and switching in an exchange. An electric selector comprises two Eo1-Ho1 transformers linked by a common circular waveguide LG so that one inlet consisting of a rectangular waveguide IG has access to a number of rectangular waveguide outlets OG. The outlets are controlled by electromagnetically controlled mechanical shutters SH, by gas discharge tubes in the guides or by gyrators. If the switching elements are omitted, the transformers provide multiple connections. A number of shuttered guides may be provided at each end of a common guide to provide a line finder/final selector link. An exchange comprises subscribers SUB1, SUB2, Fig. 10, multipled by elements M and compensating elements CE to line under/final selector links LF1/FS1 and LF2/FS2. There are separate channels for sending and receiving and each line circuit LC1, LC2 includes a hybrid transformer. The system may be made bothway by simple time division of the carrier. Signals are transmitted by amplitude modulation or by pulse repetition frequency modulation. The shutter pattern for routing a call is set up by an electronic common control not described. A distributer which can be used as a selector in a system using frequency selection, comprises a waveguide LG, Fig. 11, and a series of junctions each consisting of a resonant slot and a reflecting ring, the slots RCS1, RCS2, RCS3 and the rings RR1, RR2, RR3 being respectively tuned to carriers f1, f2, f3. An outlet is selected by selecting one of the carriers which is accepted only by its own tuned outlet. The arrangement is shown symbolically in Fig. 12. A reflex klystron is used to generate the carrier, the frequency being determined by the reflex cathode voltage. Signals are transmitted by frequency modulation. Two switching stages in a frequency selection system are shown in Fig. 13. The carrier f1 characteristic of selector D1 is demodulated at BD1 and in a manner not described, causes another carrier f2 dependent upon the route to be set up, to be transmitted and modulated at AD1. At the same time DD1 returns carrier f1 to the previous stage. The carrier f2 is demodulated by DD2 in selector D2 and, as before, another carrier is transmitted forward and modulated by AD2. Carrier f2, modulated with the backward signals received by CD2 is returned by DD2 to CD1 in selector D1. The signals are repeated by DD1 on carrier f1. A subscriber may be multipled to a number of line finders and to a number of final selectors. The waveguides may be printed or may be dielectric waveguides in which case metal may be eliminated from the speech path. Reference has been directed by the Comptroller to Specification 733,486, [Group XL (b)].