GB1403879A - Buoy position checking - Google Patents

Abstract

1403879 Radar STANDARD TELEPHONES & CABLES Ltd 9 May 1974 20441/74 Heading H4D In a position checking arrangement a control station A, Fig. 1, transmits a radio pulse of frequency f 1 at time t 0 . This is received at a transponder B and causes it to transmit a radio pulse of frequency f 2 at time t 1 . This is received at the station A and ranging equipment there determines the distance AB from the time interval since transmission of the pulse of frequency f 1 . The pulse from the transponder B is also received at the transponder C and causes it to transmit a pulse of frequency f 2 at time t 2 . This is received at the station A, and the distance BC+AC is determined. Each transponder comprises control means for causing it to transmit a pulse of frequency f 2 either in response to the reception of a pulse of frequency f 1 or in response to the reception of a pulse of frequency f 2 . The roles of the two transponders are now exchanged by means of their respective control means, and a pulse of frequency f 1 from the station A causes the transponder C to transmit a pulse of frequency f 2 . The distance AC is thereby determined, and since BC + AC is already known, the distance BC is also determined. The arrangement has particular utility for checking from a shore station the positions of the buoys marking a safe navigation channel. In such a case, one transponder may be provided ashore at a known location (Z), Fig. 3 (not shown). Transponder circuitry, Fig. 2.-A common transmit/receive aerial 20 is fed via a circulator 21, which connects it via a PIN diode switch 22 with the mixer stage 23 of a receiver. The mixer 23 receives from a varactor controlled local oscillator 24 a signal whose frequency is either (f 1 +i.f.) or (f 2 +i.f.), where i.f. is an intermediate frequency, depending upon a control signal from a master clock 25. The mixer 23 feeds an i.f. amplifier 26, the output from which goes to a detector stage 27. The detector output forms a trigger signal for a pulse modulator 28, which is driven by a power supply 29. The pulse output of the modulator 28 opens the switch 22 and causes a transmitter 30 to transmit a pulse of frequency f 2 via the circulator 21 to the aerial 20. The clock 25 is responsible for setting the transponder to one of three states, designated 0, 1, and 2. In state 0 the power supply 29 and the oscillator 24 are switched off. In state 1, the power supply 29 is switched on, and the oscillator 24 is operative at the frequency (f 1 +i.f.). In state 2, the power supply 29 is switched on, and the oscillator 24 is operative at the frequency (f 2 +i.f.). In the arrangement shown in Fig. 1, initially the transponders B, C would be at state 0. At a predetermined time the master clocks would set the transponder B to state 1 and the transponder C to state 2. After a suitable period B would be set to state 2, and C to state 1. The cycle would be completed by both transponders being reset to state 0.