| 摘要 |
PURPOSE:To achieve accurate measurement of a speed to ground without irregular switching of a high frequency attenuator due to variance in car speed, by giving a threshold value to a switching speed of the high frequency attenuator in advance and giving hysteresis characteristics to a switching speed for increase and decrease in the car speed. CONSTITUTION:Electromagnetic waves from a microwave oscillator 3 pass through a circulator 2 and are radiated from an antenna 1 to an objective car A, the reflected waves from the A are again received at an antenna 1, applied to a mixer 4 through the circulator 2 and relative doppler signal is picked up from the mixer 4 and amplified at an amplifier 5. This signal is inputted to a high frequency attenuator 7 or 8 switchingly, but since the switching speed of an attenuator switcher 6 is provided with a hysteresis characteristic depending on the increase or decrease in the car speed through a threshold value 13, irregular switching of the high frequency attenuator due to the variance in the car speed around the switching speed can not be caused. |
