Patent GB-523953-A (GB)
Title: Improvements in radio compass apparatus
IPC: G01S3/42
Filed: 1938-10-20
Abstract: 523,953. Automatic control systems. SPERRY GYROSCOPE CO., Inc. Oct. 20, 1938, No. 30371. Convention date, Oct. 22, 1937. [Class 38 (iv)] [Also in Group XL] Alignment; steering.-Radio compass or direction finding apparatus has a non-directional antenna and a directional antenna rotatable by a servomotor to maintain a null reception position and a controlling signal for the servomotor includes as a component a combination of signals from both antennµ and is applied to the motor or to a relay controlling it in such a way that the motor is immediately operated to drive a loop antenna to its null position. Antihunting means is provided to ensure dead beat operation. A centre-tapped electrostatically shielded directional aerial 2, Fig. 2, tuned by a knob 18 and condenser 32 to the wave-length of a transmitting station, is automatically maintadned in a null reception position by a servomotor 3 and selectively operated relays 17, 58, adapted to receive the output of triodes 53, 13<SP>1</SP> which respond to phase and amplitude of low frequency modulation power amplifier and detector stages 41, 48 the input to which is derived from a balanced modulator comprising a double rectifier valve 37. The output of loop 2 is fed through the valve 37 and a resistor 47 which also receives a non-directional radio signal from an antenna 9. An oscillator 43 supplies a low frequency of relatively large amplitude to the plates of the valve 37, which is merely caused to operate as an electronic switch and balanced modulator to feed a modulated R.F. signal to tube 41 the sign of which reverses in accordance with movements of the loop 2 about its null position. The input circuit of the valves 53, 53' includes resistances 69, 69' through which a current proportional to the speed of the servomotor 3 passes to prevent hunting. By means of a four-position switch 12<SP>1</SP>, 12<SP>11</SP> the output of valves 53, 53<SP>1</SP> may be directed ,alternatively from position A, in which the automatically orientated antenna serves as a radio compass, to positions B, C, D, in which the antenna remains stationary. In B a "rightleft indicator 27 is energized whereby the pilot may steer a " homing course. In C the output selectively energizes solenoids 77<SP>1</SP>, 77<SP>11</SP> controlling a fluid pressure operated gyro-pilot. In D a relay 36 is energized whereby the non- directional antenna 9 is disconnected and the loop 2 is connected across a transformer feeding into the resistance 47 giving a loop circuit shielded from electrostatic signals and facilitating oral reception by earphone 97. Manual control of the setting of the loop 2 ds obtained by a switch 73 operating on auxiliary coils of the relays 57, 58. Fig. 1 shows the arrangement of the controls which comprise in addition to the tuning knob 18 and selector switch 12, a knob 26'operating switch 73, Fig. 2 whereby the indicator needle 14 and loop 2 may be displaced, e.g., to enable a wind drift allowance to be made during pilot or gyro control, the " rightleft indicator 27, and a radio compass indicator 14 operating over compass scale 15 and actuated by flexible connection 17 from the loop orientating servomotor 3 ; a scale 23 turned by a repeater motor to show the reading of the craft's compass or directional gyro and may be turned by a knob in relation to zero so that with the aid of the pointer 14 the direct or reversed magnetic bearings of the transmitting station may be obtained. A modified drive for the loop 2 is described using a reversing induction motor the reversing fields of which are connected to the output circuits 107, 108, Fig. 3, of a double-triode amplifier 103. The output of the amplifier-detector 48 of Fig. 2 which varies in amplitude and phase according to the duration of the loop from its null position, is fed to a tube 101 serving as amplifier and phase detector. Resistances 106, 106<SP>1</SP> and inductances 105 in its output circuit develop voltages proportional respectively to the angular displacement and rate of turning of the loop and the sum of these is applied to condensers 102, 102' whereby the grids of the tube 103 experience surge voltages corresponding to the first and second derivatives of loop displacement with respect to time and hunting is prevented. In another form of motor control circuit using a two-phase motor one phase of which receives the phase detected output from the amplifier 48, an induction generator coupled to the motor injects into the control circuit a voltage proportional to its speed, to prevent hunting. A modification of the switching arrangements provided by the switch 12<SP>1</SP>, 12" of Fig. 2 is described. A dynamo-electro converting machine may supply A.C. for the low frequency modulating voltage and D.C. for the plate circuits of the valves. A two-phase motor is also described in place of the solenoids 77', 77" of the gyro-pilot. Specifications 480,766, 482,270, 482,333, [all in Group XXIX], and 500,468, [Group XXXVIII], are referred to.