GB525180A - Improvements in visual indicators for use in wireless direction finding and like systems - Google Patents

Abstract

525.180. Phase-difference measurements. STANDARD TELEPHONES & CABLES, Ltd., SCAIFE, F. N., and EARP, C. W. Feb. 17, 1939, No. 5322. [Class 37] [Also in Group.XL] In a system for the determination of direction, distance, altitude, or courses by electromagnetic radiation, of the kind in which a visual indication is given by indicating the resultant of two or more electrical vector quantities, the indicating instrument comprises a plurality of fixed field coils R1, R2, and a.moving system consisting of a rod or shaft R of magnetic material on which are mounted a plurality of angularly displaced magnetic vanes V1, V2, the rod or shaft R being encircled by one or more fixed coils E and the vanes being rotatable in the magnetic field of the fixed coils. The field coils R1, R2 are wound on flat spools and the vanes move in narrow slots therein. The coils R1, R2 are arranged with their axes at right-angles to avoid magnetic coupling. The moving system is damped by an eddy current disc T and magnets M and carries a pointer P which moves over a scale D1 marked in degrees and a further adjustable outer verge ring scale D2. A plate L shields the coil assembly from the magnets M. Fig. 1 shows the application to the radio compass described in Specification 490,940, [Group XL]. An aerial system LA1 has optimum sensitivity for east-west signals and its pick-up is modulated in a modulator M1 by an oscillator M01. A second aerial system LA2 has optimum sensitivity for north-south signals and is connected to a modulator M2 in which the signals are modulated by a different wave form from an oscillator M02. The oscillators MO1, M02 are connected to the field coils R1, R2 of the indicator. The outputs from the modulators M1, M2 are combined in an amplifier A with the pick-up from a non- directional aerial VA and after detection in a detector D the resultant modulation envelope is applied to the coil E of the instrument. The coils R1, R2 are energized at different frequencies and the coil E is energized by a combination of the same frequencies in varying amplitude and phase. The moving system takes up a position depending on the relative amounts of the frequency components and on the phase difference between the fixed and moving systems, and thereby indicates the bearing of the transmitting station. The indicator may be employed in the compass described in Specification 452,102, [Group XL], using a mechanically rotated aerial. In a modification for determining distance or altitude the phase of a transmitted wave form is compared with the wave form re-radiated or reflected by the distant object or terrain, the indicating instrument being of the type described. Such instrument may also be used in a course finder of the double tone type. Specification 162,471, [Class 37], also is referred to.