Patent GB-522574-A (GB)
Title: Arrangements for determining distance by means of radiated electro-magnetic waves
IPC: G01S13/36
Filed: 1938-12-09
Abstract: 522,574. Indicating proximity of earth or other bodies. STANDARD TELEPHONES & CABLES. Ltd. Dec. 9. 1938, No. 35969. Convention date, Dec. 10, 1937. [Class 37] [Also in Group XL] A radio altimeter or range finder comprises means for generating ultra-short wave oscillations modulated at a high adjustable modulation frequency, transmitting modulated oscillations from the generator with a negligible or constant delav to a detector and also from the generator to the ground or other reflecting surface and thence by reflection to a second detector, and comparing the phases of the detected oscillations. An oscillation generator 101 produces an ultra-short wave carrier whose frequency is higher than the modulating frequency. The waves for modulating the carrier are supplied by an oscillation generator 102 of variable frequency. The outputs from the generators 101, 102 are applied to a modulator 103, and thence to an amplifier 104 and antenna 105. From the amplifier 104 a portion of the waves are transmitted through a loss device 106 to a line 150 to serve as a standard against which waves transmitted from the antenna 105, reflected from the ground 110, and received on an antenna 109, can be compared. From the antenna 109 the received energy passes through an amplifier 120 to a line 160. The lines 150, 160 are connected to detectors 151, 161 which detect the modulated ultra-short waves so as to yield waves corresponding to their envelopes of modulation. These lower-frequency waves are applied to a phase comparison device 170. For neutralizing direct radiation between the antennae 105, 109, a small neutralizing component is led from the amplifier 104 through a phase and amplitude adjusting network 107 to the receiving antenna 109. The modulation frequency generator 102 has a dial for indicating the frequency generated and may be calibrated to indicate the length in feet corresponding to a quarter of the generated wave length. The modulation generator 102 is adjusted from its lowest frequency to the first point at which the device 170 indicates phase opposition, the dial then indicating the height directly. The comparison device 170 may alternatively indicate phase coincidence, the generator 102 then being calibrated to indicate a distance corresponding to half the generated wave length. In the phase comparison device 170 the alternating current components of the outputs of the detectors 151, 161, which are proportional to the envelope amplitudes, are vectorially added and compared with the direct-current components of the output of at least one of the detectors, the direct current components being proportional to the carrier amplitude at the input side of the detector. Each of the antennae 105, 109 consists of a horizontal radiating wire onequarter of a wave-length long, fed by concentric air-insulated lines 306, 310, Fig. 3. The antennae are grounded by vertical wires 305, 309, the central conductor of each transmission line being connected to a selected point along the L-shaped loop. The wings of the aeroplane are of metal or metal covered, the transmission lines 306, 310, being carried within the wings.