GB1475416A - Arrangement for recognising and blanking out spurious signals in the receiving branch of an interrogator - Google Patents

Abstract

1475416 Interrogator-responder systems SIEMENS AG 14 June 1974 [26 June 1973] 26583/74 Heading H4L An arrangement for blanking out spurious signals is provided in the interrogator of an interrogator-responder system of the type in which a swept band of frequencies is transmitted to the responder; from which a predetermined number of response frequencies is returned. The interrogator incorporates arrangements for identifying miscoded received response frequencies and for identifying dissimilar successively received sets of response frequencies which should be the same. These arrangements, however, will not necessarily detect errors caused by a single frequency source of interference within the sweep range. To provide for this, the receiving channel of the interrogator incorporates a mixer 82, I.F. filter 83 and amplifier 84, whose output is applied to two parallel channels 9, 11, the first including a band pass filter 91, reactifier-amplifier 92 and impulse former 93. The second similarly includes a band pass filter 111 rectifier-amplifier 112 and impulse former 113, which is followed by a counter 12 which is reset when a monostable 121 returns to its normal condition. The monostable is set to its stable condition each time a pulse output from 113 is applied to the counter, thus if pulses appear more rapidly than the delay of the monostable, the counter will keep counting. When a particular count is reached (e.g. 3), indicating the presence of spurious signals a pulse is applied to the gate 14 to prevent the pulses from the first channel (which may be delayed at 15 to allow time for the counting operation) passing to the interrogator output. It is explained that a steady interference source will produce a number of interference pulses at the output of channel 2, much closer together than coded responder pulses, since the interference is received continuously and beats with the sweep frequency (mixer 82) to produce a variable frequency ringing.