| 摘要 |
PCT No. PCT/CA95/00325 Sec. 371 Date Feb. 5, 1997 Sec. 102(e) Date Feb. 5, 1997 PCT Filed May 31, 1995 PCT Pub. No. WO95/33215 PCT Pub. Date Dec. 7, 1995A radio range finding system includes a radio range finder and a plurality of remote mobile transponders. The radio range finder transmits a signal modulated with an address code identifying a particular mobile transponder. When a mobile transponder receives the modulated signal Ms transmitted by the radio range finder and the modulated signal has been modulated with an address code that corresponds to the address assigned to that mobile transponder, the mobile transponder transponds a return signal Rs to the radio range finder. A receiver in the radio range finder conveys the received signal to a mixer which also receives an internal carrier signal identical to the modulated signal output by transmitter. The output of the mixer is then filtered and demodulated to yield an output signal proportional to the distance between the mobile transponder and the radio range finder.
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