Patent GB-585871-A (GB)
Title: Improvements in and relating to directional antennae
IPC: H01Q3/08
Filed: 1944-05-09
Abstract: 585,871. Control of motors. BRITISH THOMSON-HOUSTON CO., Ltd. (General Electric Co.). May 9, 1944, No. 8848. [Class 38 (iii)] [Also in Groups XXXV and XL] Travelling between predetermined limits; continuous reversals.-A rotatable directional antenna having a reversible drive for rotating it comprises means for producing a voltage proportional to the displacement of a directive axis of the antennas from a predetermined position and means responsive to a predetermined value of the voltage for reversing the drive. The antenna comprises a radiator 4 connected to a transmission line 3 and a parabolic reflector 5 mounted in trunnions 6 carried by supports 7 mounted on a rotatable carriage 1 and adjustable in elevation by a toothed sector 43 secured to the reflector. The turntable 1 is driven by a motor 8 through reduction gearing 9 and crown gear 11 which also drives the rotor 19 of a selsyn 18. The stator 17 of the selsyn 18 is connected to the stator 16 of a selsyn 12 having its rotor 13 preset by a handle 15 to a position corresponding to the mean position of the horizontal scan. Voltages corresponding to the displacement of the turntable from the mean position are induced in the rotor 13 and fed to a transformer 22 through an adjustable tapping point 23 on resistance 24. The centre point of coils 33, 34 in the anode circuits of a valve 27 is connected to the mid-point of a resistance 30 shunting the secondary winding of the transformer 22. When the phase of the voltage applied to the grid 25 and that applied to the anode 31 are both positive, current flows in the coil 33 which is to operate a relay 35 at a predetermined value, the displacement necessary, the required grid voltage and resulting anode current being controlled by the adjustable tapping point 23. The operation of 35 by the coil 33 opens contacts 37 at which relay 38 is deenergized and at contacts 39 reverses the supply to the motor 8. The elevational motion is controlled by a motor 40 driving the toothed sector 43 and rotating the stator 46 of a selsyn 47 so that the position of the stator corresponds to the elevation of the directive axis of the antenna. The stator 46 is journalled in a housing 49 fixed to a U-shaped frame bolted to the turntable 1. Rotatably mounted in the frame 50 is a frame 51 having a shaft 52 fixed to the rotor 53 of the selsyn 47. The frame 51 is held horizontal in a plane parallel to the vertical plane including the directive axis of the antenna by a gyroscope which is carried by a frame 54 pivoted to the frame 51 on a horizontal axis parallel to the directive axis of the antenna and which includes a stator fixed to the frame 54 and a rotor 55 surrounding the stator and provided at its lower end with a hemispherical damper 56 associated with a permanent magnet 57 supported for universal motion from the frame 54. The magnet has a short period of oscillation, and if the axis of the rotor 55 deviates from the vertical, the drag due to the eddy current in the damper 56 causes the gyroscope to precess towards the vertical thus bringing the frame to the horizontal position. The elevation of the antenna is controlled by a selsyn 59 having its stator 60 connected to the stator 46 and having its rotor 61 adjusted by a handle 62 so that any phase displacement of the rotor 53 relative to its stator 46 as compared with the pre-set selsyn 59 generates a voltage which is amplified and rectified at 63 and supplied to the fields 64 of the generator 45 to produce a control voltage for the motor 40 to rotate the stator 46 and to move the antenna to decrease the displacement. The employment of the gyroscope enables the apparatus to be used on a ship and the selsyn controls may be disposed at a distance from the antenna.