| 摘要 |
A radar interrogator (58, 100, 102) transmits an indefinite stream of radar pulses (108) to a transponder (56) at a fixed pulse repetition rate. An encoder in the transponder (56) selectively encodes a binary word representing information data (e.g.the angle subtended by two beacons (54, 56: fig.1, not shown)) to be transmitted some of the radar pulses. For example, alternate radar pulses may be inhibited (at 116) or not, to transmit the information, whilst the remaining radar pulses are retained for maintaining the distance measuring system operation. In other systems up to four successive pulses may be dedicated to a transmission of data. The same system may be used by the interrogator to transmit information. <IMAGE>
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