Patent GB-627550-A (GB)
Title: Arrangement for determining the direction of motion of moving bodies according to the reflected wave principle
IPC: G01S13/58
Filed: 1945-06-12
Abstract: 627,550. Radiolocation; adjusting radio apparatus. PATELHOLD PATENTVERWERTUNGS- & ELEKTRO-HOLDING AKT.-GES. June 12, 1945, No. 14891. Convention date, June 1, 1944. [Classes 40 (v) and 40 (vii)] In a radiolocation system wherein the exploring waves are frequency modulated by a symmetrical triangular wave-form, and beat frequencies indicative of range are obtained by mixing reflected waves with those then being transmitted, the radial velocity of a reflecting object is determined by heterodyning the beat frequencies with an auxiliary variable-frequency oscillation or oscillations in such a manner as to determine the difference, due to the Doppler effect, between the beat frequency obtained when the exploring wave is increasing in frequency and that obtained when the exploring wave is decreasing in frequency. In Fig. 1, the heavy line indicates the frequency variation of the exploring wave while the dashed and chain lines indicate the frequency variation of reflections from an approaching and a receding object respectively. It will be seen that the beat frequency has alternately different values which may be. represented as (Fd+Fv) and (Fd-Fv), where Fd is proportional to the range and Fv is proportional to the radial velocity. In one embodiment, the beat frequency signals are passed through an amplifier whose gain is doubled during the periods of decreasing frequency and thence to a mixer circuit where the beats are heterodyned with a variable-frequency oscillation f2, the mixer output being applied to a frequency spectrograph comprising a plurality of resonant units and a cathode-ray tube. When f2 is made equal to Fv, two of the side-bands produced coalesce to produce an indication of increased amplitude, at the frequencies Fd, Figs. 2 and 3. Thus the range and radial velocity are determined and the direction of the motion may be determined by noting the relative amplitudes of the displayed signals. Thus in Fig. 2 it is seen that the object is receding and in Fig. 3 that it is approaching. In a further embodiment two auxiliary frequencies are used alternately, one being applied when the transmitted frequency is increasing and the other as it is decreasing. These auxiliary frequencies differ equally by a variable amount in opposite directions from a fixed frequency so that if the summation frequencies are selected and then made equal, the summation frequency obtained will be a measure of range and the difference between the auxiliary frequencies will be a measure of velocity. In a modification of this last embodiment both the difference between the auxiliary frequencies and their mean value may be varied. The summation frequencies are arranged so that they both equal a predetermined value whereby the difference between the auxiliary frequencies is a measure of velocity and their mean is a measure of range. The beat frequencies may be applied to a common channel to which the two auxiliary frequencies are alternately applied, or they may be switched to separate channels to both of which a separate auxiliary frequency is applied continuously. If separate frequency spectrographs are used in the last arrangement means may be provided for damping the resonant units during the half cycle when no signal is being displayed. Conjoint control of auxiliary oscillators. To produce auxiliary oscillations whose mean frequency and difference frequency may be adjusted independently, the apparatus shown in Fig. 4a is used. As shown, the oscillators G1, G2 are operated by the shaft q<1> to cause their frequencies to vary together in the same direction ; by releasing the coupling q<1> and engaging the coupling q<2> the frequencies may be made to vary equally in opposite directions.