Patent GB-592596-A (GB)
Title: Improvements in and relating to radio location systems
IPC: G01S13/34
Filed: 1945-01-16
Abstract: 592,596. Radiolocation. PATELHOLD PATENTVERWERTUNGS & ELEKTROHOLDING AKT.-GES. Jan. 16, 1945. No. 1310. Convention date, Jan. 18, 1944. [Class 40 (v)] [Also in Group XXXVI] In order to indicate simultaneously the ranges of objects located at different distances in a frequency-modulated radiolocation system in which the beat frequency obtained by heterodyning the direct and reflected radiations is a measure of the range of the reflecting object, the beat-frequency output is applied in parallel to a number of narrow band-pass filters and means are provided for indicating the relative magnitudes of the filter outputs. In one embodiment, Fig. 1 (not shown), the beatfrequency output is analysed by means of a number of narrow-band-pass filters with the pass bands distributed evenly over the beat frequency range, the outputs from the filters being rectified and applied to separate indicating instruments. Alternatively the rectified or unrectified outputs are applied to separate radially-deflecting electrodes in a cathode-ray tube with a circular trace, Fig. 2 (not shown), or the rectified outputs are arranged to charge up small condensers of suitable time constant which are successively connected to the Y plate of a conventional cathode-ray tube by means of a rotary switch synchronized with the linear time base, Fig. 3 (not shown) ; to eliminate undesirable fluctuations in the indicated beat amplitude, the time bases are synchronized with the transmitter frequency variations. In a further modification, Fig. 4, the filters E1-En feeding the rotary switch U and cathode-ray tube KO are tuned to the same frequency and the beat frequency output from the receiver E is heterodyned in the modulators M1-Mn with the frequencies ul-un from the generators G1-Gn. The frequency variation from u1 to un is the same as the beat frequency range so that any beat frequency is shifted to the pass frequency of the filter by means of a particular modulator. In another embodiment the beat frequency is analysed by applying it to a tuned-reed frequency meter, Fig. 5 (not shown), with separating plates between the individual reeds to avoid coupling by the vibrating air. The movement of the reeds may be magnified optically or the reeds may be arranged to close contacts to electrically operated indicators. The beat frequency is subject to phase variations when the direction of variation of the transmitter frequency is changed and in order to prevent this causing fluctuations in the indicator the electrically or mechanically resonant portions of the indicator are damped in the neighbourhood of the extremities of the transmitter frequency. The Specification as open to inspection under Sect. 91 describes an embodiment in which the beat frequency is shifted by heterodyning it with an auxiliary frequency in order to suit the frequency range of the indicator, the indicator range being changed by switching the auxiliary frequency in fixed steps, Fig. 6 (Cancelled, not shown). A more precise indication is obtained by adding a further frequency changer with a variable-frequency beat oscillator which is adjusted to give zero deviation from a standard frequency as indicated by a discriminator circuit, Fig. 7 (Cancelled, not shown). Alternatively the frequency of the beat oscillator is continuously varied and the resultant beat output passed through a narrow band filter or discriminator to deflect or intensity-modulate the linear or circular trace of a cathode-ray tube the time base of which is synchronized with the beat oscillator variation. This subject-matter does not appear in the Specification as accepted.