GB587502A - Improvements in direction finders - Google Patents

Abstract

587,502. Radio direction finding ; artificial lines. STANDARD TELEPHONES & CABLES. Ltd., and ARMSTRONG, L. J. HEATON-. Nov. 28, 1944, No. 23751. [Classes 40 (iii) and 40 (v)] Relates to D.F. systems comprising one or more pairs of spaced aerials, the aerials being connected to a receiver by transmission lines of equal given lengths, and a non-directional aerial coupled to the receiver by a transmission line of length different from the given lengths. According to the invention, means are inserted either in the transmission lines connected to the spaced aerials or in the transmission line connected to the non-directional aerial for maintaining the relative phase of the signals at the receiver constant over a broad band of frequencies. The invention is described as applied to an Adcock aerial as used in the D.F. system disclosed in Specification 490,940 in which the signals from each opposed pair of aerials 1, 2 and 3, 4 are combined in opposition due to the transpositions in the coupling lines 6, 7 and the resultant signals are fed over lines 9 and 10 to the receiver where they are modulated with different frequencies, the resultant modulation products being combined with a signal from the omni-directional aerial 5 and fed to a cathode-ray tube indicator. In such a system, the resultant signal from a pair of spaced aerials 1, 2 may be brought into phase with the signal from the omni-directional aerial 5 by making the length of the line 6<1> from each aerial to the line 9 equal to A/4, i.e. total length of line 6 equals #/2, the length of the line from aerial 5 being then made equal to line 9 ; such an arrangement only holds for a single frequency and in order to obtain correct phasing over a broad band of frequencies, e.g. 30- 100 Mc/s., the length of line 61 is made less than #/4 and a phase advance network 16 is inserted in the line from aerial 5 such that the sum of the phase lag in line 61 and the phase advance in network 16 is equal to 90 degrees for all frequencies within the band. The equivalent # network 15 for a line 6<1> of electrical length 0 degrees is shown in Fig. 5 and if tho inverted form of this, Fig. 6, is used as the phase advance network 16, the necessary conditions are met since the phase lag of line 6<1> increases with frequency and the phase advance of network 16 decreases with frequency. Alternatively, the phase-advance network could be inserted in the lines from the dipole pairs.