Patent GB-753069-A (GB)
Title: Improvements in or relating to speed measuring devices employed in railroad car retarder control systems
IPC: G01S13/58
Filed: 1954-05-13
Abstract: 753,069. Radar; aerials. GENERAL RAILWAY SIGNAL CO. May 13, 1954 [June 2, 1953], No. 14036/54. Class 40 (7). The invention relates to an arrangement for determining the speed of moving railway vehicles, particularly during bump shunting, and for automatically controlling track retarders in accordance therewith. It is intended for use in a system such as is described in Specification 746,443, [Group XXXIV]. In accordance with the invention a radio signal is directed towards each vehicle as it approaches the retarder and an output signal derived dependent on the frequency difference between this signal and that reflected back from the vehicle. A plurality of electromagnetic relays are selectively actuated by the output signal in accordance with the vehicle speed. Fig. 1 shows a transmitting and receiving aerial 10 placed towards the outlet end of a vehicle retarder. It is fed with a continuous signal from oscillator 11 and its receiving element feeds the received doppler shifted signal reflected by the vehicle (if one is approaching) and a proportion of the transmitted signal to crystal mixer 12 from which a doppler shift beat frequency signal is obtained. This is fed through pre-amplifier 13 to amplifier and pulse former 14 whose output is a series of pulses at the input signal repetition frequency. These pulses are fed to each of relay control circuits 15, 16, 17 and 18. These control circuits operate their respective relays at varying pulse repetition rates to control the operation of the retardation selecting circuits 20 controlling the retarder. Control 15 may operate for a rate corresponding to half a mile an hour speed of vehicle travel and serve to give an indication of vehicle approach while controls 16, 17 and 18 operate for high, medium and lower speed vehicle approaches respectively. The circuits 20 may be modified in accordance with the weight of the approaching vehicle if a weight detector is placed as shown a short distance before the retarder. The actual speeds at which the relays associated with 16, 17 and 18 operate may also be modified by a manual control 23 in accordance with such features as the curvature of the track over which the vehicle is to travel. The beat frequency signal from pre-amplifier 13 is also fed to relay control 19, the relay of which picks up when the amplitude of the signal indicates a vehicle is in close proximity and drops away when the vehicle has passed over the aerial horn 10 to allow the resetting of the retardation controls. The circuit of the arrangement is described with reference to Figs. 2A, 2B and 6 (all not shown). Aerials.-The aerial 10 comprises a transmitting element 32 and a receiving element 33 situated in line at the focus of a parabolic cheese reflector 31 which provides a beam 10 degrees wide horizontally and 30 degrees wide vertically directed along the track. The transmitting element 61, 62 is a folded unipole having an attached ground plane 58. The central element 61 is extended -through sleeve 59 to form a probe inserted an adjustable length into cavity resonator 24 attached to the outside of the reflector for feeding energy to the element. The receiving aerial 33 is also a unipole with the upper surface of the horn as its counterpoise. The aerial element 157 is mounted on a holder containing a crystal rectifier 161 so that the beat frequency signal is fed out at 158 directly to the preamplifier 13 (Fig. 1).