Patent GB-576555-A (GB)
Title: Improvements in wireless direction finding receivers
IPC: G01S1/02
Filed: 1938-03-19
Abstract: 576,555. Directive wireless systems. HECHT, N. F. S. March 19, 1938, Nos. 8531 and 19289. [Class 40 (v)] A wireless direction-finding system comprises an azimuth phase aerial, the output of which is of constant amplitude but of phase dependent upon the direction of incoming signals, and a constant phase aerial. The mixed output of the aerials, which has an amplitude modulation depending upon the relative phases, is rectified and fed together with a steady current via a rotor coil associated with two stator coils to the deflector plates of a cathode-ray oscillograph, so that the polar diagram traced due to rotation of the aerial system and rotor coil is an inverse pseudo-cardioid with the maximum peak sharply defined. The azimuth phase aerial system 1 comprises crossed loops connected to isolating devices 2, 3 which also so tune the loops that their outputs are in quadrature. The resultant output of the loops and the output from a constant phase aerial 5 are fed via coupling coils 4 and 6 to coil 7. The combined output, the amplitude of which varies sinusoidally as the aerial 1 is rotated is amplified and rectified at 12 and fed to the rotor coil 13 which is coupled to the stator coils 14 and 15 feeding the deflector plates 16, 17, 18, 19 of the cathode-ray oscillograph, and is rotated with the aerial 1. In order that the diagram traced on the oscillograph should be an inverse cardioid, a continuous current obtained by separate amplification and rectification at 20 of the output from aerial 5 is applied in series to the rotor 13. The steady current component may be of arbitrary value and obtained from any source and may be adjustable to cause the peak of the inverse cardioid to coincide with a circular scale for ease of reading. As an alternative to rotation of the crossed loops of aerial 1, which may be replaced by an Adcock system, the aerials may be coupled to the field coils of a goniometer, the search coil of which comprises two loops at right angles and arranged to produce currents in quadrature. In a further modification, Fig. 2 (not shown), a potentiometer is substituted for the rotor 13 and fixed coils 14 and 15. A plate of resistance material has a voltage applied across it corresponding to the current in coil 13, while four brushes connected to the cathode-ray tube deflector plates are rotated over the resistance plate so that two potentials in quadrature varying sinusoidally with the rotation of the brushes are fed to the opposite pairs of plates. It is stated that a three deflector plate cathoderay tube may be employed in conjunction with a potentiometer provided with three equallyspaced brushes. An alternative aerial arrangement which is free from polarisation errors, comprises four pairs of crossed loops spaced at the corners of a square, the circuits of each pair being arranged to provide output currents in quadrature. Diagonally opposed pairs of loops are combined in opposition, the loops in parallel planes being connected in opposition and the differential effects of such combination being added vectorially and fed to one stator coil of a goniometer, the rotor of which consists of two coils at right angles. The other diagonally opposed pairs of loops are similarly connected to the second stator coil. With this arrangement employed for the azimuth phase aerial, the constant phase aerial is replaced by a centrally positioned pair of crossed loops also quadrature tuned, the combined output of which changes in phase by #/2 for a change of azimuth of #/2 whereas the phase of the combined. dual search coil currents varies by # for the azimuth change of #/2.