GB993105A - Decoder-encoder for beacon system utilizing a single delay line - Google Patents

Abstract

993,105. Transponder apparatus. BENDIX CORPORATION. Jan. 27, 1964 [Feb. 8, 19631. No. 3405/64. Heading H4L. A transponder is provided with a single tapped delay line which decodes a group of interrogating pulses of one polarity and also provides a different coded group of reply pulses of the opposite polarity. As shown in Fig. 2, in an air traffic control system, the interrogating pulses 31, 32 after detection in the transponder are supplied via a video amplifier 16 to a delay line driver 33 which provides an additional negative pulse 35 derived from the output of the tapped delay line 34 when an interrogating signal is recognized. The output of device 33 is also supplied to a coincidence gate 37 and when the correct interrogating signal as determined by the setting of a selector switch 38 is received the pulses 31, 32 coincide at gate 37 and a pulse is supplied via a delay 41 to a trigger a pulse generator 43 and supply the negative pulse 35. Application of the negative pulse 35 to the delay line 34 provides coded negative output pulses in accordance with the setting of reply code selector switch 44, the two output circuits of the delay line being isolated from each other by oppositely poled diodes, and the coded pulses are supplied via a limiter 45 to a coincidence gate 47. Pulse 35 also triggers a generator 29 to operate an oscillator 46 which generates shaped pulses which are passed by the gate 47 to a modulator in accordance with the reply code. The generator 29 also supplies a signal blocking the amplifier 16 when the reply signal is being transmitted. Provision may be made, Fig. 3 (not shown), for automatically switching the reply from an identification signal to a p.c.m. signal representing the altitude of the aircraft in accordance with the type of interrogation signal received.