Patent GB-600073-A (GB)
Title: Radio identifying system
IPC: G01S13/78
Filed: 1945-03-16
Abstract: 600,073. Radiolocation ; radio signalling. STANDARD TELEPHONES & CABLES, Ltd. March 16, 1945, No. 6744. Convention date, March 18, 1944. [Classes 40 (v) and 40 (vii)] In a system for identifying a number of radio pulse responder stations, the interrogator transmits successively a number of pulse trains of different recurrence frequency and each responder or group of responders of the same category is responsive to a particular recurrence frequency, means being provided at the interrogator for indicating and identifying the received pulse train. The responses may be indicated on a cathoderay tube or they may be applied to light indicator lamps. The system is suitable for a ground station interrogating aircraft. As shown in Fig. 1, pulses are radiated from the interrogator transmitter 36 which is controlled by the pulse generator 34 the recurrence frequency of which is successively varied by the switch 46. The output from the interrogator receiver 42, which is blocked during transmission of the pulse by means of the circuit 40, is applied to the cathode-ray tubes 60, 62, 64 provided with separate timebase circuits 50, 52, 54 which are successively synchronized with the different recurrence frequencies by means of the switch 46. Each responder, e.g. 12, comprises a continuously radiating squegging oscillator tuned to one of the recurrence frequencies and when that particular recurrence frequency is radiated by the interrogator the oscillator is locked so that a stationary response appears on the correponding cathode-ray tube indicating the range of the responder. If a number of responders of the same category are operated at the same recurrence frequency they may be distinguished by differing pulse widths. The outputs from the receiver and the time-base circuits are also fed through switched or variable filters 66 and 68 which select components of the same recurrence frequency and apply them in opposite phase to the coils of the relays 70, 72, 74 by means of the phase-reversing and mixing circuits 99 and 92. When a signal of the selected recurrence frequency is received the two components balance out and the relay coils are de-energised closing the contacts to light the lamp, e.g. 70, which is selected by the switch 76 but in the absence of a received signal of the selected recurrence frequency there is no output from the filter 66 and the output from filter 68 energizes the coils and opens the contacts in the lamp circuits. Switches 46, 58, 76 and the variable filter 68 are ganged together and either driven by the motor 84 or operated manually. In a modification, Fig. 2 (not shown), the responses are presented on a single cathoderay tube supplied by a single time-base circuit which is varied in synchronism with the changes in recurrence frequency. The responses due to responders operating at different recurrence frequencies are distinguished by applying to the cathode-ray tube brilliance pulses of a higher recurrence frequency than the recurrence frequency of the system the widths of the pulses varying with the changes in recurrence frequency to give full line, dotted or dashed responses. The receiver may also be adjustable to be responsive only to pulses of the selected recurrence frequency. The Specification as open to inspection under Sect. 91 also illustrates in Fig. 3 (Cancelled, not shown) a pulse radar system suitable for use as an airborne interrogator in which the receiver output is applied to trigger a circuit producing a series of square waves the leading edge being determined by the transmitted pulse and the trailing edge by the echo pulse so that the pulse duration is proportional to the range. The leading edge of the square wave initiates the production of a sawtooth wave and the' trailing edge cuts it off so that the amplitude of the sawtooth is proportional to the range and this is indicated by a peak voltmeter. For use in identifying responders, the receiver is adjustable to be responsive only to pulses of the recurrence frequency generated by the variable frequency pulse generator. This subject-matter does not appear in the Specification as accepted.