Patent GB-644061-A (GB)
Title: Vehicle communication and location indicating system
IPC: B61L3/22
Filed: 1947-08-08
Abstract: 644,061. Indicating movements and position of trains. STANDARD TELEPHONES & CABLES, Ltd. Aug. 8, 1947, No. 21931. Convention date, Jan. 16, 1946. [Class 105] [Also in Group XL (c)] A communication or location indicating system for a vehicle following a fixed route comprises a transmitting and receiving terminal, a non-radiating transmission line extending from the terminal along said route, a plurality of decouplers connected to the line at spaced intervals each carrying radiating means extending along the route, and signal translating means on the vehicle having an antenna radio coupled with the nearest adjacent radiating means. As shown, multiplex pulse communication and marker (synchronizing) pulses on a frequency f 1 are transmitted from a West terminal rail station along a coaxial line 3 between it and an East terminal, including at intervals repeaters R and decouplers D, similar communication pulses from trains and marker pulses from the East terminal synchronizing the train transmitters being transmitted Westwards on a frequency f2. Twin wire transmission lines 9, 10, radiating horizontally polarized frequencies f1, f2 respectively, or carriers on which f1, f2 are modulated, mounted on poles on the same or opposite sides of the track and terminating in high impedances 13, extend along the track between decouplers and from the West terminal and are radio coupled with antennas 11, 12 on the trains. The decouplers, Fig. 3, comprise filters and amplifiers for the frequencies f1, f2, feeding back to the line 3, and feeding f1 or a carrier on which it is modulated to twin lines 9, for reception by train-receiving aerials 11. Each decoupler also extracts, by a pulse width selector 30, synchronizing marker pulses eM modulated by the East terminal on frequency f2, feeding them on a frequency f2, or a higher frequency, if necessary, to the radiation lines 10 for reception by train aerials 12, and synchronization of train transmitters using the same aerials 12 for transmission, and includes a receiver 32, blocked during operation of the marker pulse transmitter 31, passing signals from the trains on the lines 10 to the coaxial line 3 on a frequency f2. Communication between trains takes place via a West terminal switchboard. Separate coaxial cables may be used for each radio frequency. If a decoupler is disabled only that adjacent portion of the track is rendered inoperative for communication purposes. Every 25th marker pulse WM transmitted by the West terminal may be a wide " radar " pulse WR producing on trains or at the terminals a visible spot on an expanded circular time base of a cathode-ray tube mounted on the trains and at the terminals indicative of the position of the West terminal. The pulse repetition rate of pulses WR also synchronize the time bases. Each pulse WR received by trains and East terminal (on frequency f1), after reshaping to narrower pulses t<1>, t<11> .. TE, which may be given a code flicker indicative of the train t<1>, t<11>... concerned or of the East terminal, is then retransmitted as an echo pulse on a frequency f2, and after reception at West terminal retransmitted on frequency f1, the only frequency the trains and East terminal can receive on lines 9. The position of all trains and of the terminals is thus proportionately indicated on the tubes and the train speeds may be estimated. The marker pulses eM or WM each comprise a pair of closely spaced pulses, the second being an echo produced by a delay line. The marker pulse selectors similarly comprise a delay line superimposing the pulses so that they exceed in amplitude and are extracted from the communication pulses by a biassed clipper. The train transmitted location pulses t<1>, t<11> and East terminal location pulse TE are wider than the communication pulses but only about one-half the width of the complete marker pulse and so not selected by the marker pulse selectors. They are selected by a pulse width selector on other trains and at terminals with a tuned anode circuit having a period twice the width of the pulses so that the leading and trailing edges of each pulse greater than a certain width (but not the double marker pulses), cause an oscillation exceeding in amplitude the threshold bias of a clipper valve which extracts the pulses. Alternatively they may be selected using a delay line and slipper as in the case of the marker pulses. At the West and East terminals multiplex timemodulated communication pulses are produced from a series of phase displaced sine waves of frequency 10 kc/s. derived from a delay line and modulated, and the channel repetition frequency made 10 kc/s. One channel may be used for automatic or other train control. On trains the pulse communication frequency is f2 and the transmitter 157 (Fig. 11, not shown) synchronized by marker pulses eM received on a frequency f2 by a receiver 158 from the East station, different channels being selectable using a delay line 161. This is passed to the coaxial line via the transmission lines, received at a West terminal switchboard and retransmitted if necessary to other trains or the East terminal on the frequency f1. Filters exclude the radar pulse repetition frequency of 400 c/s. and harmonics. At the East terminal the marker pulses eM are derived from West terminal marker pulses WM and the echo pulse TE slightly delayed so as to fall between each of the elements of the marker pulse pair eM. In a modification, instead of the location echo pulses being superimposed intermittently on one or other of the communication channels the location pulses are arranged to fall all within one particular channel. To this end the marker pulse repetition frequency on frequency f1 from West terminal and on frequency f2 from East terminal are independent and made 10 kc/s. and 11 kc/s. respectively, and the terminal and train equipment switched so that location pulses, which thus occur (11000-10000)/25 or 40 times per second, are only unblocked during that channel. Hum (400 c/s.) filters are not then required. In a further modification only the decoupler block location of a train is transmitted West, each decoupler giving a particular width to the location pulses from the trains which pulse width is selected at the West terminal and used to illuminate a corresponding lamp denoting a block occupied. The pulses may be produced from West terminal marker pulses WM or independently generated by trains and are given an identifying flicker. The location pulses may, as before, be arranged to fall within a particular channel. A pulse width selector circuit is described and also a marker pulse pair generator and selector employing reflection from one end of a delay line. The pulse modulators and demodulators may be as described in Specifications 592,584, [Group XL], 600,272 and 638,345, [both in Group XL (c)], or of cathode-ray tube type as described in Specifications 603,188, 603,614, and 635,482, [all in Group XL (c)].