Patent GB-790360-A (GB)
Title: Phase comparison radio direction finding systems
IPC: G01S3/46
Filed: 1946-02-15
Abstract: 790,360. Radio direction-finders. STANDARD TELEPHONES & CABLES, Ltd. Feb. 15, 1946 [Feb. 17, 1945; Feb. 19, 1945], Nos. 4827/46 and 4828/46. Class 40 (7). In a phase comparison radio direction-finder wherein the outputs from two spaced aerials are applied through respective continuously varying phase-shifting devices to a receiver which indicates equality of phase of the received signals, the two separate outputs from the phase-shifting devices are so coupled together that substantially no current is taken by the receiver when equality of phase is achieved. The aerials 1, 2 are connected to earth through separate transmission lines which include artificial line portions 7 and 8 respectively and resistive terminations 11 and 12. The lines 7 and 8 are coupled to the receiver 18 by the variable tapping points 13 and 14 which are caused to execute a simple harmonic motion over a length of line equivalent to the spacing between the aerials by means of the crank 27 on the continuously rotating wheel 24, driven by motor 22 which also drives the deflecting coil 21 about the cathode-ray tube 19. The output from the receiver 18 wherein the signals taken from the tapping points 13 and 14 are combined differentially is used to modulate the radial deflection on the cathode-ray. tube so that a predetermined deflection is obtained twice per revolution of the disc 24 at the null points, where the phases of the signals applied to the receiver are equal. The signals taken from the tapping points 13, 14 are coupled together by coils 29 and 30 and so inject voltages into each other that substantially no current is taken by the receiver at the null points, and thus prevents the production of standing waves on lines 7 and 8 which would otherwise cause errors in the null position. Alternative phase shifting means not involving the use of sliding contacts may be used, Fig. 2 (not shown). Fig. 6 illustrates a further embodiment of the invention similar to that illustrated in Fig. 1. The two transmission lines comprise outer conductors 67 separated by insulating material from the inner conductors 68 and are here shown in transverse section. These lines are arcuate and subtend approximately 90 degrees at the axis 84 in a plane perpendicular to that axis, Fig. 4 (not shown). Plates 80, 81 which mesh with the inner conductors 68 to become capacitively coupled therewith are rotated about the axis 84 in synchronism with the rotation of the deflecting coil of the cathode-ray tube display unit. The axis 84 provides a conductive connection between the arms 82 and 83 but it is situated a quarter wavelength away from the plates 80, 81 at the operating frequency so that it behaves as an open circuit at the tapping points. The tapping points are coupled together by a device 86, illustrated in greater detail in Fig. 7, which converts the balanced transmission line feed to a coaxial line feed. The output from the device 86 is taken by means of the coaxial transmission line through the plug 54 to the receiver. It will be seen that the converting device takes no current when the voltages applied thereto are equal in amplitude and phase and that therefore at the null points no standing waves are set up on the lines 67, 68. Specification 685,990 is referred to.