GB1028294A - Improvements in or relating to electrical apparatus of the kind for detecting the existence of a predetermined timing relationship between two electric pulses - Google Patents

Abstract

1,028,294. Pulse radar. GENERAL ELECTRIC CO. Ltd., W. HADDOCK, R. H. KIRKNESS, and C. J. WAYMAN. Feb. 13, 1964 [Feb. 15, 1963], No. 6349/63. Heading H4D. [Also in Division G4] A pulse train received from an aircraft transponder includes two reference pulses which are spaced in time by a fixed interval T. The pulse train is supplied to a shift register 4, Fig. 1 (not shown), and to another shift register 6 after being delayed by T at 3. Clock pulses having a repetition frequency sixteen times that of the pulse train, are applied to the shift input 7 of the registers 4, 6. Normally, the delayed first reference pulse enters register 6 at the same time as the second reference pulse enters register 4, the two pulses are shifted through the registers in synchronism, gates 9, 11 are opened simultaneously as the pulses reach stage IV of the registers and gate 13 produces a coincidence signal indicating that the reference pulses are correctly spaced. A variation of plus or minus one clock pulse period is accepted by means of gates 8, 10 which enable gate 13 when stages III and V store a pulse. On receiving the coincidence signal from gate 13, counter 25, Fig. 2 (not shown), starts to count clock pulses, and supplies a pulse over lead 37 to step a counter 41, Fig. 4 (not shown), once every sixteen clock pulses, i.e. at the repetition rate of the received pulse train. Counter 41, by way of diode matrix 42, enables bi-stable circuits 45 in turn so that the pulse train taken from stage I of register 6 via a bi-stable circuit 28, which is enabled by sampling signals from gate 3, is staticized and may be supplied to a decoder. A second unit 19 and staticizer may be used for a pulse train received whilst unit 18 is being used. Garbling is detected by bi-stable circuits 31, 32, Fig. 2. Circuit 31 is enabled by gate 2 during the first half of each pulse period of the received train. If the first reference pulse of another train occurs during one of these intervals (called first-pulse garbling), circuit 31 is set by the coincidence signal from gate 13. If a pulse from another group is received when a pulse of the sampled group is expected (called main-garbling) the interfering pulse, on reaching stage III of register 6, enables circuit 32 when the sampling pulse from gate 3 occurs and circuit 32 is set. The setting of either of circuits 31, 32 causes counter 41 and staticizer circuits 45 to be reset.