Patent GB-1219424-A (GB)
Title: Improvements in or relating to inductive signalling systems for vehicles
IPC: B61L3/22
Filed: 1968-01-10
Abstract: 1,219,424. Inductive signalling; radio signalling; aerials; measuring speed by radio waves. SUMITOMO ELECTRIC INDUSTRIES Ltd. 10 Jan., 1968 [12 Jan., 1967; 16 Feb., 1967; 20 March, 1967 (4); 18 June, 1967], No. 1390/68. Headings H4A, H4D, H4L and H4U. In a signalling system for communicating with vehicles, e.g. railway trains, a transmission line comprising a pair of conductors 5, 6, Fig. 5, wound around a cylinder 4 of insulating material at an equal and constant pitch and separated by half the winding pitch extends along the space between the rails 1 and cooperates with a pair of antennas 7, 8 on the train. The signal to be transmitted is supplied to the conductors 5, 6 and the resulting magnetic field is reversed at points separated by half the winding pitch so that the radiation field tends to cancel and becomes effectively zero, similar considerations applying to incoming interference signals. The antennas 7, 8 are arranged so that when the received signal in one is a maximum it is a minimum in the other, and the output of one is phase shifted and the two signals combined to recover the transmitted signals. Alternatively the two antennas may be spaced on the vehicle at points which are one quarter of the winding pitch apart, Fig. 9 (not shown), or with two antenna pairs, one half of the winding pitch apart, Fig. 10 (not shown). Transmission may be in either direction. The transmission line may consist of 3 or more conductors wound around a cylinder as previously described, each conductor being supplied with the signal phase-shifted by 2#/n from the signal in the adjacent conductor where n is the number of conductors. Various methods of constructing and supporting the transmission line are described, Fig. 17, A to I, and Fig. 18 (not shown). An antenna for a vehicle, Fig. 19, comprises two pairs of conductors 34, 36, each pair being short-circuited by wires 32, 33, respectively, and the wires being wound as described for the transmission line. Signals from the transmission line received by the antenna differ in phase by #/2 in the two pairs 34, 36 and are phase-shifted and combined at 30. Measuring speed.-It is stated that the received frequency changes in proportion to the train speed divided by the winding pitch of the transmission line and this may be used to measure the train speed. In one arrangement, Fig. 27 (not shown) the received signal is compared with a reference frequency on the train identical to the frequency applied to the transmission line. In a further arrangement, Fig. 28, the signal #o is supplied to a pair of transmission lines 64 1 , 64 2  of left and right hand winding respectively. The signals received by antennas 65 1 , 65 2  have frequency deviations in opposite directions and after combination at 67 the frequency deviation is derived and hence the speed. In a modification, Fig. 29 (not shown), the signal #o is fed to a single transmission line but one antenna feeds a phase-shifting circuit providing oppositely changing output signals which may be combined as before. In another embodiment, Fig. 30, frequency #o is supplied from the fixed station 63 to the transmission line 64, received by the antenna 65, amplified at 68 and returned via the antenna 65 and transmission line 64 to the station 63 where it is compared at 67 with the frequency #o to derive the frequency deviation.