Patent GB-929359-A (GB)
Title: Distance measuring system
IPC: G01S13/36
Filed: 1961-04-17
Abstract: 929,359. Radar; transponder apparatus. BENDIX CORPORATION. April 17, 1961 [May 12, 1960], No. 13827/61. Addition to 862,485. Classes 40 (5) and 40 (7). Relates to a modification of the amplitudemodulated CW secondary radar system disclosed in the parent Specification for determining the distance between the interrogator and responder at the interrogator by phase comparison of the transmitted and received modulation signals and in which the interrogator and responder transmit at the same carrier frequency during sequential periods, e.g. each of duration 0.1 sec. approximately, the modulation signal at the interrogator is derived from a tuning fork oscillator 26, Fig. 2, the modulation signal received at the responder drives a tuning fork oscillator 58, Fig. 3, which modulates the reply signal and the modulation component of the reply signal received at the interrogator is compared with an output from the tuning fork oscillator 26. According to the present invention the tuning fork oscillator 26 at the interrogator, Fig. 2, includes a normally closed positive feed-back path 27 which is opened by a switch 3K1 for a 0.5 sec. period SS 22, Fig. 4A, commencing with the interrogation transmission period SS 18 and the tuning fork oscillator 58 at the responder, Fig. 3, includes a negative feed-back path with a normally open switch 3K1 which is closed for a 0.5 sec. period 68, Fig. 4B, on completion of the reply transmission period 65 so that the tuning fork resonators at the interrogator and responder operate as freely oscillating structures during the periods in which signal information is applied thereto or extracted therefrom, the amplitude of the interrogator tuning fork oscillations being built up before the interrogation transmission period SS 18 by positive feed-back and the responder tuning fork oscillator 58 being damped by negative feed-back before reception of the interrogating signal. A single interrogation transmission period may be initiated by a push-button 14, Fig. 2, or such periods may be initiated cyclically by a multivibrator 17. Interrogator, Fig. 2. The output from the tuning fork oscillator 26 is applied via a switch 2K2 to the transmitter which is keyed by a switch 2K1, the switches 2K1, 2K2 being actuated by a relay 2K controlled by the output SS 18, Fig. 4A, from a monostable circuit 18 triggered by the leading edge of the output SS 20 from a monostable circuit 20 triggered by the input trigger pulse from the push-button 14 or multivibrator 17 which also triggers the monostable circuit 22 giving an output SS 22, Fig. 4A, which operates relay 3K to open the switch 3K1 in the positive feed-back circuit 27 of the tuning fork oscillator 26. The modulation component of the reply signal from the receiver is applied at 13 through a gate 31 (closed during the interrogation period by the output SS 20, Fig. 4A, from the monostable circuit 20), filter 32, pulse shaping network 44 and gate 37 together with the pulse shaped output from the oscillator 26 to a pulse phase comparator 38, 41, 42, 46, 45 similar to that disclosed in Specification 862,485, the gate 37 being opened (period SS 37, Fig. 4A), by the output 35, Fig. 4A, from a bi-stable circuit 35 which is triggered on in response to the coincidence of received signals and locally generated tuning fork signals in a gate 33. The phase comparator is rendered operative during a " read " period SS 36, Fig. 4A, by a switch 1K1 actuated by a relay 1K operated by a monostable circuit 36 triggered by the trailing edge of the output SS 19 from a monostable circuit 19 triggered by the trailing edge of the output SS 18 from the monostable circuit 18. During the interrogation period SS 18 any previous distance reading on the meter 45 is erased by a voltage produced by closure of a switch 2K3 by the relay 2K. Responder, Fig. 3. The modulation component of the interrogating signal is applied at 51 through a gate 55 and filter 56 to drive the tuning fork oscillator 58 and outputs from the filter 56 and oscillator 58 are applied to a coincidence gate 62 to trigger a bi-stable circuit 64 giving an output 64, Fig. 4B, whose trailing edge triggers a monostable circuit 60 whose output 60, Fig. 4B, blocks the gate 55 during the reply transmission period 65, Fig. 4B, which is determined by the output 65 from a monostable circuit 65, Fig. 3, triggered by the leading edge of the blocking waveform 60. The output 65 operates a relay 2K to close switches 2K1 and 2K2 thereby keying the transmitter and applying an output from the oscillator 58 thereto and the trailing edge of the output 65 triggers a monostable circuit 68 which operates a relay 3K to close the switch 3K1 in the negative feed-back path of the oscillator 58. Fig. 5 (not shown) illustrates an apparatus comprising a single tuning fork oscillator which may be used selectively as an interrogator or responder according to the setting of a plurality of switches.