Patent GB-1485827-A (GB)
Title: Communication system for guideway operated vehicles
IPC: G08G1/00
Filed: 1974-08-19
Abstract: 1485827 Communication system for guideway vehicles TRANSPORTATION TECHNOLOGY Inc 19 Aug 1974 [20 Aug 1973] 36384/74 Headings H4U and H4L [Also in Division B7] A communication system for a vehicle moving along a predetermined path includes a transmission line 52<SP>1</SP> extending along the path and including at least three conductors 54, 56, 58 (Fig. 4) each having a wave configuration offset from the others such that they are relatively equally phase displaced. An inductor loop 50, Fig. 6, on the vehicle couples with the transmission line and is energized with a continuous wave signal, so that signals whose envelopes vary in amplitude as a function of displacement along the path are induced in the conductors. A receiver coupled with the line detects the signals and from their envelope frequency and phase sequence provides outputs indicating the speed and direction of the vehicle. Furthermore, the system enables data and voice communication between the vehicle and a base station to take place. Fig. 4 also indicates the configuration of the return conductor 72 relative to the three offset conductors. At the base station (Fig. 9) a carrier f is  derived from an oscillator 178, passes synthesizer 176 and is applied to the line via adder 200 and amplifier 220. It may be mixed at 200 with a modulated voice signal from channel 210 and/or modulated data from channel 202. The signal from the amplifier 220 is applied to the three phase line via coupling circuitry (Fig. 5, not shown). Signals from the 3 phases of the line are derived from the same coupling circuitry and applied to, e.g. A, B, C inputs 130, 132, 134. Two sets of inputs are provided, to allow for the fact that signals may be coming from lines to either side of the vehicle, depending on the route that this is taking through junctions and the position of the arm on the vehicle which carries the transmitting/receiving coils. Presence or absence of a signal on the A line is detected, after filtering and amplification, at 164 to indicate which line is in use: signals from the alternative B and C lines are summed at 156, 158 and the resultant filtered, amplified and applied to respective squaring circuit 157. The squares are summed at 162 to provide a signal which is phase independent of the particular conductor. This signal is applied as feedback via amplifier 184 to the conductor amplifiers and is passed on to detectors 188, 194 where any data or speech modulated signals carried by it can be demodulated using carrier references developed from the frequency synthesizer 176. By measuring the envelope frequency of signals received from a particular conductor at 166 the vehicle speed can be ascertained and by counting the zero crossings the position of the vehicle in the system can be recorded. By noting A, B, C phase sequence at 168 the direction of motion can be determined. At the vehicle, there are two pick-up coils in figure eight configuration 110, 112 (Figs. 4 and 6) displaced relative to each other by 90 degrees by reference to the conductor patterns in the track lines. These coils are surrounded by the transmitter coil 50. The signals V 1 , V 2  picked up from the two coils are filtered, amplified, squared and then added at 230 to provide a signal independent of phase position. After filtering this signal is used to provide feedback via amplifier 244 and a reference for the modulating and demodulating frequencies produced in the vehicle circuitry by frequency synthesizer 248. The frequencies generated by this are used to demodulate the received signal at 242, 254, 256 to produce voice and data information at the vehicle and also to modulate, at 286, 294, 290, voice and data information to be transmitted by the vehicle to the base station.