Patent GB-1396821-A (GB)
Title: Ranging systems
IPC: G01S13/76
Filed: 1973-03-22
Abstract: 1396821 Pulse radar ELLIOTT BROS (LONDON) Ltd 30 Jan 1974 [22 March 1973] 13765/73 Heading H4D A two-way ranging system comprises means at a first station (e.g. an airborne station) for transmitting an interrogating signal to a second station (e.g. a ground station), means at the first station for decoding its own transmission and recording the time of so doing as a first point C, Fig. 1, in time, means at the second station for receiving the interrogating signal, decoding it and recording the time of so doing as a second point E, transmitting a response signal to the first station, sampling its own transmission to produce a test signal which is applied to the R.F. input circuit of its own receiver for decoding and recording the time of so doing as a third point H, and means at the first station for receiving the response signal, decoding it and recording the time of so doing as a fourth point K. The time interval P between the points C, K is indicative of the distance separating the two stations. In order to compensate for variable delays in the second station due to temperature changes, ageing &c., the time interval M between the point E, H is made equal to a predetermined value by adjusting the time of triggering of its transmitter (point F). This is done by measuring the interval FH, which is made up of Tg, the time between the triggering of the ground station transmitter and the commencement of transmission from its aerial, and Rgg, the further time until the ground station decodes its own transmission, and thereafter making m (i.e. E.F) equal to M- (Tg+Rgg). As described, airborne equipment (Fig. 2, not shown), comprises a transmitter which is triggered via a control circuit by a clock and which transmits a pair of appropriately spaced interrogating pulses to a selected ground station. The transmitter is connected to the aerial via a circulator and a first coupler, and a sample of the interrogating signal is fed from said coupler via a sample mixer and a second coupler to a receiver. Output from the receiver is decoded in a decoding circuit and is applied to a range computing circuit, which also receives clock signals, and which provides output signals to a utilization terminal. Response signals from the ground station which are received by the aerial are coupled by the first coupler to the circulator, which is connected to a further input of the second coupler. Said response signals are processed by the receiver &c. as were the interrogation signal samples. In a ground station, interrogating signals received on an aerial 13, Fig. 3, are applied via a first coupler 19, a circulator 14, and a second coupler 21 to a receiver 15. If recognized by a decoding circuit 16 as intended for the station, a control and delay circuit 17 triggers a transmitter 18, which is connected to the aerial 13 via the circulator 14 and the coupler 19, and which transmits a two-pulse response signal, the time interva between said pulses serving to identify the station. The coupler 19 samples the response signal, and said sample passes via a sample mixer 20, the coupler 21, the receiver 15, and the decoding circuit 16 to the control and delay circuit 17, where it is utilized as described above for adjusting the triggering of the transmitter 18.