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Abstract

Method and apparatus for measurement of the velocity of a moving target (20) in radio frequencies. From the measurement station (10) and from the target station (20), radio signals (S.sub.1,S.sub.2) are transmitted that are in different frequency ranges, as compared with each other, so that the receivers at the measurement station (10) and at the target station (20) are not subjected to interference. The radio signals (S.sub.1,S.sub.2) are received at stations (20,10) opposite to their transmission stations (10,20). The oscillator of the target station (20) is locked with the frequency transmitted by the measurement station (10) by means of a phase-locked loop (PLL). The frequency of said oscillator is passed to the transmitter part of the target station (20). The signal (S.sub.2) transmitted by the target station (20) is received at the measurement station (10). The Doppler shift (fd) of the frequency of the signal (S.sub.1) transmitted from the measurement station (10) and of the signal received at the measurement station is measured, and the velocity (v) of the moving target to be measured is determined on the basis of the Doppler shift.

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