Patent GB-987081-A (GB)
Title: Delay compensation in telemetering systems
IPC: G01S13/66
Filed: 1961-07-21
Abstract: 987,081. Electric selective signalling systems. STANDARD TELEPHONES & CABLES Ltd. July 21, 1961 [July 22, 1960], No. 26593/61. Heading G4H. [Also in Division H4] In a system for telemetering to a beacon the range of a craft as measured by the latter, and in which a transmitter at the beacon interrogates a transponder on the craft to trigger a single pulse telemeter signal therefrom, the range indication at the beacon will be in error due to finite transit wave propagation times between the beacon and the craft. In order to obviate this error, the beacon comprises means 5 Fig. 3 to generate a signal at a first frequency F, means 6 to generate a signal at a frequency S < F and synchronized to signal frequency F, and a counter 7 running from means 6 and stopped by the reply signal from the craft. The apparatus on the craft comprises a signal source 13 providing F pulses/sec. triggered by the beacon transmission and feeding a counter 14 which is stopped by a signal from a known rangemeasuring system 15 (e.g. a "TANCAN" distancemeasuring system) and which issues a pulse for transmission to the beacon. The embodiments employ radio but soundwaves may be used. The principle of the invention is described with reference to Figs. 1A, 1B and 2 (none shown). In a typical radio embodiment frequencies F and S are 200/sec. and 199/sec. respectively, and the maximum range of the system is 403 miles. Range display device 8 may be neon lights to indicate binary numbers, or a digital voltmeter presenting decimal numbers, or an illuminated decimal number display. Telemetering of second independent variable, Figs. 4, 5. To telemeter a second variable, e.g. temperature, utilizing the same pulse as for range, each range interval is divided into B (e.g. 360) subdivisions. At the transponder Fig. 5 pulses at frequency F issue from unit 36 after receipt of the pulse from the beacon and start range counter 39; when the range counter stops a signal is sent to AND gate 46 and a unit 40 producing B pulses for each range interval is started at the beginning of each range interval. Counter 43 is stopped at the sub-division corresponding to the measured value of the second variable and a pulse is fed from the counter to AND gate 46 for transmission to the beacon. At the latter Fig. 4 sub-division generator 36 is synchronized with range counter 31 so that for each one count of the latter the B pulses issue from unit 29. The transponder pulse received at the beacon stops range counter 31 and temperature counter 33 simultaneously. Telemetering from plurality of craft, Fig. 8. The transponders on the craft are each as in Fig. 3 or Fig. 5; the beacon apparatus is as illustrated in Fig. 8 for transponders as in Fig. 3. At the instant of beacon transmission pulses at frequency S from unit 6 cause all counters 7, 50, 51 to operate. When the return pulse from the nearest craft is received, counter 7 is stopped and a memory unit 54 prepares an AND gate 56 to receive the pulse from the next nearest craft and stop counter 50; similarly counter 3 registers the range of the third craft. The apparatus of Fig. 8 is also applied to the two-variable embodiment of Fig. 4. The beacon may be stationary or on a ship or on another aircraft.