| 摘要 |
A vehicle identification system includes a doppler radar producing a doppler frequency signal having noise components and having a value fD corresponding to the speed of the vehicle to be identified and a doppler frequency having a value XxfD corresponding to the speed of the vehicle propelling means, each doppler frequency being modulated by signals corresponding to the movements made by individual elements of the vehicle propelling means. The doppler signal is passed through first and second adjustable filters adjusted to pass fD and xxfD respectively and sidebands relating to the modulating signal. Amplitude detectors coupled to the outputs of the two filters remove the doppler frequencies leaving the modulating signals relating to the movement of the vehicle elements. The modulating signals are applied to an adjustable commutating filter adjusted to frequency by a signal corresponding to frequency fD. The output signal from the commutating filter represents sounds made by the vehicle individual elements by which one can identify the vehicle as to type.
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