Patent GB-685990-A (GB)
Title: Radio direction finding system
IPC: G01S1/02
Filed: 1945-09-07
Abstract: 685,990. Directive radio systems. STANDARD TELEPHONES & CABLES, Ltd. Sept. 7, 1945 [Sept. 11, 1944], No. 23171/45. Class 40 (vii). A radio direction-finding system comprises two antennµ spaced apart and matched to an interconnecting transmission line including a delay network providing a time delay equivalent to the electrical spacing of the antennµ and continuously varying coupling means connecting a radio receiver to successive points on the delay network. Such a system normally gives an ambiguous bearing indication and two pairs of interconnected aerials, the systems being at right angles, may feed into a common receiver to provide a single indication. Two antennµ 1 and 2 spaced apart preferably less than half a wavelength are connected through matching devices 4 and 5 to line 3 which includes an artificial line 8 provided with movable contacts 9. Line 8 is made electrically equivalent to the spacing between the antennµ so that the null of the directive pattern is rotated linearly through 360 degrees as the contacts 9 are moved along the line 8 in simple harmonic motion by means of crank 20 on disc 17 driven by motor 15. Deflection coil 14 of the cathode-ray tube indicator is also rotated by motor 15 and the output of receiver 11 connected to contacts 9 is applied to the coil to produce a pattern, such as that shown, which indicates the bearing of the transmitter from which signals are being received on a circular scale marked round the screen. Instead of using a null to indicate bearing, the cross-connection 6 in the line 3 to aerial 2 may be dispensed with and maximum indications used instead. In a system, Fig. 4, having no ambiguity of indication, two mutually perpendicular antenna systems.1, 2 and 28, 29, connected respectively by lines 3 and 30 including artificial lines 8 and 31 with movable contacts 9 and 32 are used. Contacts 9 and 32 are synchronously moved along these lines by means of cam 20 on disc 17 driven by motor 39 and the signals therefrom are added out of phase to prevent spurious indications before application to receiver 11. The output from contacts 32 may be shifted approximately 180 degrees to bring it into opposition with energy from brush 9 to provide a null indication. In this embodiment a different form of indicator having deflection plates fed from two phase generator 40 driven by motor 39 is used and the output of the receiver is applied by means of coupling arrangements 37 and 38. The simple antennae shown may be replaced by arrays if desired and the contacts 9 and 32 capacitively rather than conductively coupled to the artificial lines. It is also possible to use linear movement of the contacts if either the rotation of the deflection system or the calibration is according to a sine wave function. Two variable artificial lines may be used for each pair of antennae, one connected to each antennµ and each presenting a constant impedance to the joint receiver if the lines are simultaneously adjusted so that the sum of their tune delays is equivalent to the electrical spacing of the antennµ. Specification 581,998 is referred to.