| 摘要 |
An echo ranging system comprising a code generator, the output of the code generator is used to bi-phase modulate a carrier frequency signal. The modulated signal is then transmitted towards a target from a system antenna. A return echo signal is delayed with respect to the transmitted signal by the effective target range. Further, the output of the code generator is delayed so as to be phase aligned with the transmitter leakage or spillover signal at a mixer. The code on the leakage signal is then removed and the carrier is attenuated in a notch filter. The coded echo signal is not reconstituted since it is not in time synchronization and is coded a second time at the mixer. With a round trip range equivalent to a half word code period, the doubly coded echo will appear as if it were generated by an oscillator at twice the frequency. The twice frequency coded echo signal then passes through the notch filter virtually uneffected and is coupled to a second receiver demodulator. The second input to the demodulator is the code originally generated but at a frequency twice that of the original coder clock frequency. The higher frequency coded echo is then demodulated.
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