Patent GB-564572-A (GB)
Title: Improvements in or relating to directional radio receiving systems
IPC: G01S3/42
Filed: 1942-07-03
Abstract: 564,572. Automatic control systems. SPERRY GYROSCOPE CO., Inc. July 3, 1942, No. 9260. Convention date, July 3, 1941. [Class 38 (iv)] [Also in Groups XXXVII and XL] Relates to direction-finders comprising a directional and a non-directional aerial or, in a modification, two directional aerials movable together in which the pick-up from one aerial 1 is modulated at low frequency f<SP>1</SP> in a balanced modulator 18, the resulting side bands being combined with the pick-up from the other aerial 26 and then rectified to give an output lowfrequency current, the amplitude and phase of which depend upon the orientation of the directive aerial, as in Specification 523,953. According to the invention, an A.V.C. voltage derived from a harmonic of the modulation frequency is applied to the pick-up from the directive aerial so as to regulate the ratio of the two signals and maintain the output substantially constant except when the directive aerial is substantially in the null position. The combined output from the amplifier 23 passes through the converter and I.F. amplifier 31 to a valve 33 which functions as a dual amplifier and rectifier. The signal of intermediate frequency is amplified and fed back through transformer 34 to diode electrode 35, thereby producing a low-frequency current f<SP>1</SP> in filter 38 and resistance 39. The voltage across 39 is applied through condenser 41 to the grid of valve 33, so that the low-frequency current is amplified, the voltage drops across resistance 42 passing through amplifier 43 to the telephones 44. The L.F. voltage across resistance 39 is also used to supply A.V.C. voltage to valve 13 by selecting a harmonic of the fundamental frequency by the filter 61. The selected frequency is amplified and rectified by valve 64, an increase of D.C. voltage across 66 being used to reduce the gain of valve 13, thereby preventing the signal from the directive aerial from rising above a certain level, determined by the optimum ratio of the pick-ups of the two aerials. The gain of the valve 23 and converter 31 is controlled by the potential across a resistance 74 in circuit with a second diode electrode 72 and resistances 75, 76, so chosen that no output appears across 74 until the peak voltage applied to 72 exceeds the bias voltage across 75, 76, thus producing delayed A.V.C. on valves 23, 31. The L.F. voltage across resistance 39 is also used to control the twophase (split-phase) motor 3 driving the aerial 1. To this end, the L.F. voltage is applied through filter 46, and amplifier 47 in push-pull to the grids of gas-valves 49, 50. The local modulating current from source 21 is also applied in phase to the grids, thus producing an output determined by the magnitude and phase of the input, as in Specification 417,995, [Group XXXVIII]. This output is applied to the motor 3, which rotates in a direction determined by the phase of the voltage across resistance 39, which in turn is determined by whether the directive aerial requires movement to left or right to bring it into the null position. To prevent hunting; an auxiliary generator 53 furnishes an auxiliary control voltage proportional to the speed of the motor, as described in Specification 446,665, [Group XXXVIII]. Aerials. The non-directive aerial may be replaced by a second loop, at right angles to the first, but functioning in much the same way as the non-directive aerial in Fig. 1A. The two loops may be mounted at right angles on the same shaft, connections being made by slip rings, Fig. 3 (not shown). The Specification as open to inspection under Sect. 91 also states that the A.V.C. voltage applied to valve 13 may be derived from the fundamental frequency f<SP>1</SP>. This subject-matter does not appear in the Specification as accepted.