Patent GB-556759-A (GB)
Title: Improvements in or relating to radio direction finding systems
IPC: G01S1/02
Filed: 1942-04-17
Abstract: 556,759. Wireless direction-finding apparatus. STANDARD TELEPHONES & CABLES, Ltd. (International Standard Electric Corporation). April 17, 1942, No. 5119. [Class 40 (v)] In a radio direction finder of the kind in which the incoming signals are modulated by a rotatable directional wave-collecting system, from the output of which waves in phase quadrature are obtained and applied to the deflecting means of a cathode-ray oscillograph or like indicator, the waves in phase quadrature are obtained from the two fixed coils of a goniometer the movable coil of which is rotated in synchronism with, and supplied with signals derived from the rotating wavecollecting system. In order that the outputs from the fixed coils of the goniometer shall, after rectification, be sinusoidal, and not in the form of half-waves, means are provided either for adding to the outputs from the fixed coils a proportion of the waves supplied to the rotatable coil, or for adding a proportion of the unmodulated incoming waves to the output of the rotating wavecollecting system. In the system shown in Fig. 2, the incoming signals are modulated by a rotating aerial or radio-goniometer system F, and after rectification in a receiver RR (giving unidirectional half-waves as shown in Fig. 3), are fed to a modulator MOD where they modulate a carrier wave of, for example, 100 to 200 kilocycles supplied from a generator G. The output from the modulator is applied through a transformer T3 to the terminals 7, 8 of the rotatable coil of a radiogoniometer GC, which is rotated synchronously with the system F. The terminals 1, 2 and 3, 4 of the two fixed goniometer coils are connected through transmission lines L1, L2, or directly, to detectors D1, D2 the outputs of which are applied to the pairs of deflecting plates of a cathode-ray indicator K. A proportion of the output of the modulator MOD is added to the outputs from the fixed goniometer coils by transformers T1, T2, thus ensuring that the modulated carrier supplied to L1 and L2 has a value always greater than zero, the envelope being of sine wave form as shown in Fig. 8. The resulting indication on the screen of the oscillograph is of needle-shape, similar to that obtained in the known apparatus employing a rotating resistance potentiometer to supply the waves in phase-quadrature to the oscillograph. In a modification, Fig. 4 (not shown) a single valve generates and modulates the carrier wave, which is then applied to a transformer having one secondary winding connected to the rotating coil of the goniometer and another which supplies the extra series voltages to the outputs from the fixed coils. In a further modification, Fig. 5 (not shown) balanced inputs are provided for the deflecting plates of the oscillograph by the use of double-diode rectifier valves connected to both ends of the fixed goniometer coils, the midpoints of which are connected to the respective ends of the winding of a transformer supplying the extra series voltages to the outputs from the fixed coils. In another arrangement, Fig. 6 (not shown) the extra series voltages are separately transmitted by three-wire transmission lines to a distant indicator point or to more than one, before being combined by means of transformers with the modulated waves. The system shown in Fig. 7 gives an indication free from sense ambiguity. A receiver comprising a diode V4 and amplifying valve V5 is fed, through transformers T15, T16 having their secondaries in series, with unmodulated signals from an aerial A and modulated signals from the wave-collector F, the voltage of the former being preferably large compared with the latter. The resulting wave is applied to the terminals 7, 8 of the goniometer GC, and is a uni-directional sinusoidal voltage which produces a maximum only once during the revolution of the beam of the oscillograph. By suitably biasing the valve V5 the beam may remain undeflected from its central position except in the immediate neighbourhood of the maximum position, so giving a narrow indicating curve.