| 摘要 |
<p>PURPOSE:To measure directly a ground speed, by converting a Doppler history by an isolated reflection body to a pulse train, and measuring the number of this pulse, and the start point and end point time of the pulse. CONSTITUTION:A coherent radio wave of a transmitter 1 is irradiated from the diagonal upper direction to the surface of a track 8 from an antenna 3, a reflected signal from a crosstie 6 is led to a mixer 9, and it is mixed with a part of transmitting electric power. When the antenna 3 moves by a constant speed (v), a variation output of the expression S is obtained in the output terminal of the mixer 9 (in the expression, (a), lambda, (v), T0 and gamma0 denote a proportional constant, wavelength, a vehicle speed, time when the antenna passes through just above the crosstie, and length of a perpendicular line put down to the crosstie on the track, respectively). When a signal exceeding a threshold level obtained in the beam irradiation width is amplified by a pulse generating circuit 10 which is capable of obtaining a Doppler history by putting a vehicle running distance vt to a horizontal axis, and is converted to a pulse train, the running distance can be represented by the number of pulses. Accordingly, when the necessary time extending from the start point of the first pulse to the end point of the n-th pulse is measured by a counter 11, a speed can be calculated by an operating circuit 12, and acceleration is obtained by measuring a variation rate of said time.</p> |
