Patent GB-550131-A (GB)
Title: Improvements in or relating to radio direction finders
IPC: G01S3/42
Filed: 1940-06-20
Abstract: 550,131. Automatic control systems. LEAR AVIA, Inc. June 20, 1940, No. 10644. Convention date, July 27, 1939. [Class 38 (iv)] [Also in Groups XL and XXIV] In a system in which a loop aerial, operating in conjunction with a non-directional aerial on an airplane, is automatically rotated to its null position with respect to received radiation, a clutch is provided to prevent over-running or hunting. The direction of the transmitting station is shown on an indicator 64, Fig. 1, in the cockpit, or the movement of the aerial may effect automatic pilotage. The system may also be used for ordinary wireless reception, when the loop can be oriented manually. The loop-orienting motor 30 is controlled by an electron-tube relay system 45, which receives audio-frequency oscillations from a generator 31 by a direct path through amplifier 43 and also by a path, extending from a modulator 32 to an amplifier 40, wherein it is modified in accordance with the yield of the aerials. Automatic orientation of aerial.-Oscillations picked up by the loop aerial 10, Fig. 2, pass through amplifier 47 to modulator 32, where they are combined with audio-frequency oscillations at 102.5 c/sec. from the generator 31. The conditions are such that valve 86 of the modulator is active for one half-period of the audio frequency, while valve 86<SP>1</SP> is active for the other half. By transformer 24 and amplifier 80 the modulated loop signals are combined with the signals from the non-directional aerial 20, the output from which has its maximum amplitude in the first or the second half of the audiofrequency cycle according as the loop 10 is oriented to the right or to the left of the null signal position. Hence, when the combined signals are demodulated by a mixer valve 120 and audio-frequency detector 140, the phase of the demodulated signal depends on the orientation of the loop aerial. The demodulated signal passes by way of audio-frequency amplifiers (including a final amplifier 190) and a phase-shifter 162 to a relay control system 45, which also receives audio-frequency oscillations direct from generator 31 through amplifier 43. The demodulated signals are applied to starter anodes 330,3301, Fig. 4, of valves T, T<SP>1</SP> (which may be thyratrons or, preferably, cold-cathode glow-discharge tubes with starter anodes) of relay system 45, while the unmodified audio-frequency oscillations arriving through amplifier 43 are applied to the anodes 332, 332<SP>1</SP> of these valves. The bias is such that one valve or the other becomes active according as the demodulated voltage applied to the starter anodes (which are in phase with one another) agrees in phase with the voltage applied to one or other of the anodes 332, 3321, and according, therefore, as the loop aerial errs to the right or to the left of its null position. Solenoid S or S<SP>1</SP> is energized accordingly, and a circuit is closed to run motor 30 in one direction or the other, so as to turn the loop 10 towards its null position by the shorter path. The position of the aerial is telegraphed to the cockpit by means of a resultant-field system (Fig. 10, not shown) after mechanical correction for quadrantal error. The loop is prevented from overshooting its null position by the use of a high ratio in the reduction gear which drives it, and by being declutched from the motor shaft at the requisite moment by a magnetic clutch operated by the current which drives the motor. Further, the tube T, Fig. 4, or T<SP>1</SP>, as the case may be, which acts to reverse the direction in which the loop has been rotating may have its sensitivity increased by alteration of its bias through the movement of armatures 58 or 53, so that overshooting is promptly reversed. Alternatively the relays S, S<SP>1</SP> may have additional contacts which vibrate so as to interrupt the circuit of the active tube T or T<SP>1</SP> at a low frequency, Fig. 5 (not shown), or the battery supply of the motor may be similarly interrupted by an automatic electrical vibrator, Fig. 6 (not shown). Delayed automatic volume-control of the modulated signals is governed by a biased rectifier 210, Fig. 2, which is fed with an intermediate frequency signal from amplifier 134, so that the outputs of all stages up to the first audio-frequency stage 150 are raised to a constant level. Manual alternative gaincontrol is provided at 220, 222. In the relay system, Fig. 4, and in the oscillator 31 and amplifier 43, the B voltage derived from the point 320 is held constant at point 315 by a voltage-regulator 200, which may comprise a coldcathode glow-discharge tube. The motor 30 may drive the loop aerial 10 directly through a clutch and a bevel gear, Fig. 1, or through a reversible friction gear, Fig. 11, in which case the motor runs continuously and the leads 361, 3611, instead of feeding the motor, feed two solenoids 515, 5151 which operate the gear. Facilities additional to automatic directionindication.-Audio-frequency modulation of signals received by the aerials is dealt with at the same time as the locally produced oscillation of 102.5 c/sec., and both audio-frequencies are heard by the pilot in the telephone receivers 175, Fig. 2. Alternatively he can, by turning switch 100 to its top position in Fig. 2, connect the loop aerial alone for receiving messages, the local audio-frequency oscillator 31 being then disabled by disconnection from earth at a, while the biasing of modulator 32 is so altered that only one, 86, of its valves is in action, and this acts as an amplifier. The loop 10 can then be rotated manually, or automatic loop-rotation can be temporarily set up by closing the earthing-switch 95. Continuous-wave reception can be brought in by means of switch 225 if desired. A mile-meter 240 comprises a milliammeter fed by the current of the automatic volume-control governed by the rectifier 210. The readings of the mile-meter correspond to the strength of the received signals and therefore to the distance of a given transmitter : it thus resolves ambiguity when the loop aerial is used alone for direction-finding, and indicates passage over a transmitter. When the switch 100 is in its middle position the non- directional aerial 20 alone is in operation, so that the apparatus may be used for receiving messages or beacon-range signals ; oscillator 31 is cut off from earth at c, and modulator 32 is disabled by the cutting in of the over-biasing resistance 91. The loop aerial may be rotated manually as well as automatically ; gears suitable for this purpose are described with reference to Figs. 7, 8 and 9 (not shown). Instead of controlling the loop-orientating motor, the leads 361, 3611 may control an automatic pilot, Fig. 12 (not shown), whereby the plane is steered in the direction for which the loop has been set. Friction gearing.-In order that the continuously running motor 30, Fig. 11, may be enabled to rotate the loop aerial 10 in either direction, or to be disengaged from it the loop is mounted on a ring 502 having a frictional surface 506 which engages one or other or neither of two cones 503, 504 on a motor-driven shaft 505, according as the shaft is moved to the right or the left, or disengaged, under the control of the solenoids 515, 5151. Specification 523,953 is referred to.