Patent GB-622349-A (GB)
Title: Improvements relating to communication systems for trackway vehicles
IPC: B61L15/00
Filed: 1947-03-14
Abstract: 622,349. Railway communicating systems. WESTINGHOUSE BRAKE & SIGNAL CO., Ltd., March 14, 1947, No. 7111. Convention date, June 25, 1946. [Class 105] [Also in Group XL (c)] Communication between stations and vehicles on a trackway is established by a pair of line wires L 1 , L 2  extending along the track inductively coupled with communication apparatus on the vehicles, both wires in parallel forming with their distributed impedance to ground a " longitudinal " circuit, and in series a metallic " transverse " circuit, and by repeater stations located at intervals along the track to transfer the signal currents in the lines from a transverse to a longitudinal circuit of the lines and vice versa alternately. In Fig. 1b (showing part of a railway division with terminal station E) low and high frequency carrier bands are used for communicating from stations to trains and from trains to stations respectively. Multiplex transmissions on different frequencies pass from the station E through a low-pass filter LDF and condensers 11, 12 to the transverse circuit of existing telegraphy pole lines L 1 , L 2 . The distant repeater point AE receives the transverse energy via filters 17, 19 and amplifier 18 and retransmits longitudinal energy to the lines through condensers 23, 24. This energy may be picked up by receivers RA on trains V 3  or V 4  with coils 10 inductively coupled with the lines. At a further repeater point BE the longitudinal energy is selected by filters 26, 28, amplified and passed as transverse energy beyond the point via leads 29, 30. The train transmitters TA first energize the track by feeders connected between pairs of front and rear wheels, the track then inductively energizing the lines L 1 , L 2  with longitudinal energy. This is translated to transverse energy by repeater e.g. AE, via condensers 23, 24, high pass filters 20, 22, amplifier 21 and leads 8, 9 station E receiving this energy via condensers 11, 12 and filter 46. The division is divided into three sections by filters LPF passing only D.C. or very low, e.g. speech frequency, currents but blocking carrier frequencies so that trains can intercommunicate with either station when on the centre section but only with the nearer station when on end sections. Condensers 11, 12 block very low signal frequencies from the receivers, and filter LPF and coils 61 prevent carrier frequencies passing beyond station E. The coils 61 are coupled to present only low impedance to transverse energy to enable communication beyond station E by further station apparatus. Chokes L 3 , L 1  prevent transmission of energy along other lines on the same pole. In Fig. 2 (not shown) different bands of carrier frequencies are used for transmission in different directions, e.g. east and west, along the lines. Low pass filters, as before, blocking carrier frequencies divide the system into three sections to prevent two repeaters simultaneously repeating the same energy. The terminal stations feed longitudinal energy to the lines and a transfer point CD in the centre section converts transverse energy therein into longitudinal without amplification. Trains in this case can communicate with each other and with either station at any time. U.S.A. Specification 2,064,642 is referred to.