| 摘要 |
An apparatus for detecting a vehicle ground speed, including a transmitter for transmitting a wave towards a ground surface, and a receiver for receiving a portion of the transmitted wave reflected by the ground surface. The apparatus produces an output indicative of the vehicle ground speed, according to a Doppler effect on the basis of the frequencies of the transmitted wave and the reflected wave, and further includes a device for changing the frequency of the transmitted wave so that the sensitivity of the receiver is held within a predetermined optimum range. The device is adapted to restrict or inhibit a change in the frequency of the transmitted wave due to deterioration of the condition of the ground surface which causes the receiver sensitivity to be lowered.
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