US1991443A - Direction finder - Google Patents

Description

Feb. 19, 1935.

H. l. BECKER DIRECTION FINDER v FLEXIBLE CABLE.

2 Sheets-Sheet 1 Inventor":

Howard LBecker,

H is Attorney Feb. 19, 1935. LBECKER I 1,991,443

DIRECTION FINDER Filed Oct. 26, 1932 2 Sheets-S heet 2 r A Fig. 2. B HIHHHIH "nnnnnnn HIHHHH JUUUUUUL uuuuup' DESTINATION Inventor: Howard I. Becker,

H is Attorneg.

Patented Feb. 19, 1935 UNITED "ST TES 1,991,443 DIRECTION rmnnn Howard I. Becker, Schenectady,- N. Y., asaignor to General Electric Company, a corporation of New. York Application October 26,

1932, Serial 1%.639576 My invention relates to direction-finding systems and more particularly to improved directionfinding means foruse on mobile craft, such as ships, airplanes, etc., whereby a response in accordance with a route to be followed may be obtained.

My invention has for one of its objects to provide an improved direction finder which will provide both substantially constant angular sensitivity and symmetrical angular indication.

- Another object of my invention is to provide a radio direction finder utilizing a substantially instantaneously responsive non-linear resistor, and which will produce symmetrical angular indications.

A further object of my invention is to provide means for insuring symmetrical angular indication in a direction finder.

In my copending application, Serial No. 556,605, filed August 12, 1931, entitled Automatic steering system, and which is assigned to the same assignee as my present application, I have disclosed a system in which the course to be traveled by a mobile craft with respect to a. stationary point, such as the destination of the craft, is predetermined by adjustment of the equipment on the craft itself and which avoids the necessity for marking out the course as by means of aradio beacon system. .1

A further object of my invention is to provide a simplified direction-finding receiver for operation with such a system of automatic steering.

The novel features which I believe to be characteristic of my invention are set forth with particularity in the appended claims. My invention itself, however, both as to its organization and method of operation together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawings in which Fig. 1 represents an embodiment of my invention and Figs, 2 and 3 illustrate certain characteristics of its operation.

. Referring to Fig. 1, I have shown the directionfinding equipment at the lower portion of the fig ure. The equipment is provided with a directive antenna 1 which I have shown in the form of a loop, and a non-directive antenna 2. The directive antenna 1 is provided with the step-up transformer 3, located in close-proximity to the loop structure, which serves to transfer the oscillations received by the loop antenna to the input circuit of the?receiving discharge device 4.

The primary winding of the transformer 3, which is connected .to the loop antenna 1, is arranged in the form of a coil concentrically mounted about the shaft which supports the antenna,

audit is rotatable with the antenna. The secondary winding of the transformerti, which is connected to the input circuit of the'discharge 5 device ,4, is stationary and is arranged concentrically with'respect to the primary'winding. This arrangement permits transfer of energy from the loop antenna 1 to the input circuit of the discharge device 4 with great selectivity and sensi- 10 tivity; and without any of the disadvantages incurred by the use of a slip-ring and contact arrangement. The non-directive antenna is 'connected to the gridof an electron discharge device 5. The anodes of both discharge devices 4 l5 and 5 are connected in parallel andarranged to supply amplified oscillations to the input circuit of a suitable demodulator 6. The demodulator is provided with an automatic volume control for maintaining constant the sensitivity of indi 20 cation of the angular position of the loop antenna.

A variable capacitor 7 is arranged to tune the secondary winding ofthe transformer 3 to pro vide eflicicnt directive reception. The grid circuit ofthe electron discharge device 4 also includes 25 a coupling device 8 wherebylow frequency oscillations generated by the electron discharge device '9 are impressed to vary the bias upon the grid and therefore the amplification of the discharge device 4. By connecting a resistor 10 in the grid circuit of the electron discharge device 4 and by properly adjusting the grid bias upon discharge devices 4 and 9, the low frequency modulation impressed upon the oscillations received by antenna 1 is an' 35 asymmetrical fiat topped and peaked bottom wave. Obviously, of course, any other form of circuit which will provide modulation which is asymmetrical may be used, or the oscillator may be arranged to supply an asymmetricalwave to the 0 modulator. The purpose of obtaining this distorted wave form will become apparent during the explanation of the operation of the direction finder. Thus, the electron discharge device 4 cperates as a-modulator of the oscillations received v 4 to any other spect to the direction of the propagation of the received waves. The combined oscillations are transmitted to the demodulator 6 where demodulation currents are obtained and transmitted to an output circuit. The demodulator 6 and the variable capacitor 7 are simultaneously tuned and controlled by means of a remote control unit operating through a fiexible cable.

, In order to provide symmetrical angular indication, that is, equal indications for equal angular rotation of the directive antenna from the null position, an adjustable potentiometer 11 is provided. This potentiometer is connected between the cathode of electron discharge device 5 and the source of filament potential. The movable contact of the potentiometer is connected to the grid circuit return lead of the discharge device to which the vertical antenna 2 is connected. The adjustment of the potentiometer, which varies the bias on the grid of electron discharge device 5, controls the relation of the oscillations received by the vertical antenna 2 with respect to the oscillations received by the directive antenna 1 so that symmetrical indication is obtained. This arrangement prevents the energy from either antenna from predominating over the other, thereby insuring symmetrical indication.

The output circuit of the demodulator 6 is provided with a transformer 12 so that messages may be received by means of a pair of headphones. A zero center direct current meter 13 serves to provide directional indication in response to the demodulation currents present in the output circuit. A filter circuit 14 is connected between the meter 13 and the output circuit to exclude all frequencies except the demodulation frequency corresponding to the frequency generated by the electron discharge device 9. This filter circuit prevents the meter 13 from responding modulation currents, thus. stabilizing its operation. The demodulation currents are passed through this filter circuit and a nonlinear resistor 15 to the meter. This non-linear resistor 15 is preferably of the type described in United States Patent No. 1,822,742 issued September 8, 1931 to K. B. McEachron. The resistance and current relationship of such non-linear resistor material can be expressed in the form of a simple hyperbolic equation: R=C' where R is the resistance, I is the current, and C and a are constants. The exponent a is less than unity and the constant 0 preferably ranges between, and 600. This material has the peculiar property of reacting substantially instantaneously to asymmetrical wave shapes so that a direct current fiows in the circuit, but when symmetrical waves are passed through it, no direct current fiow occurs. This direct current fiow may be in either direction dependent upon whether the positive or negative values of the asymmetrical wave shape are greater. The resultant direct current fiow actuates the meter 13 to give directional or right and left indication. In other words, the meter indicates the direction which the loop antenna 1 must be rotated to place it in a null position. A by-pass capacitor 16 serves to shunt the alternating currents around the meter 13.

If the loop antenna 1 is at right angles to the direction of the propagation of the received waves, then no received oscillations are impressed upon the grid of the discharge device 4, and accordingly the only oscillations supplied to the demodulator 6 are those received from the whereas if the loop is moved in the vertical antenna 2 and amplified by amplifier 5. If the loop antenna is moved in one direction, however, from the null position, oscillations are received upn the grid of device 4 which may com bine with the oscillations received from the nondirective. antenna in opposed phase relation, whereas if the loop antenna is moved in the opposite direction, these oscillations will combine with oscillations received from the non-directive antenna in like phase relation. Thus, the oscillations which are supplied to the demodulator 6 from the non-directive antenna 2 are increased or decreased, dependent upon the position of the loop antenna 1. If the oscillations received from the two antennae combine in phase, then the oscillations supplied to the demodulator 6 are of maximum value when the amplification of the discharge device 4 is at a maximum, and similarly, the oscillations supplied to the demodulator 6 are minimum when the amplification of the discharge device 4 is minimum. If the loop antenna 1, however, is in such position that the two oscillations combine in opposed phase relation, then the oscillations supplied to the demodulator 6 are maximum when the amplification of the discharge device 4 is minimum, and vice versa. Thus, as a result of the demodulation of the oscillations supplied to the demodulator 6, currents having a frequency of the source 9 are reproduced and supplied to the output circuit. These currents are of asymmetrical wave shape which are inverted when the antenna currents are combined in opposed phase relation. If the loop is at right angles to the direction of wave propagation, no oscillations are received from the loop antenna 1 and accordingly, no oscillations having the frequency generated by the discharge device 9 appear in the output circuit. If the loop is moved to one position from the null position, oscillations appear in the output circuit having a certain distorted wave form,

opposite direction from the null position, oscillations appear in the output circuit which are of an inverted distorted wave form.

These currents appearing in the output circuit are passed through the non-linear resistor 15 and dependent upon the wave shape, produce direct current flowing in one of two directions which in turn, actuates the meter 13 to give a directional indication. Thus, for instance when the directive antenna is rotated in one direction, the resulting demodulation currents may be such as to cause a direct current flow through'the meter 13 in one direction, whereas if the antenna is rotated in the opposite direction, the demodulation currents will be such that a direct current will flowv through the meter 13 in the opposite direction.

For a better understanding of the operation described above, reference may behad to Fig. 2.

The wave form A shows a carrier wave such as is received by the non-directive antenna 2 and impressed upon the demodulator 6 by means of the electron discharge device 5. A similar wave of lesser amplitude is received by the directive antenna 1 when the loop antenna is rotated at anangle to the null position. The carrier wave received by antenna 1, however, may or may not and the grid bias potential on the electron discharge devices 9 and 4, these oscillations shown in wave form B are distorted when modulated upon the oscillations received by loop antenna 1. The distorted modulated oscillations present 'in the output circuit of electron discharge device 4 are combined with those present in the output circuit of the electron discharge device 5. In one position of the directive antenna 1, these currents will be in like phase relation and will combine to produce a wave of the form illustrated at C. The oscillations shown in wave form C when passed through the demodulator 6 produce'in the output circuit distorted low frequency currents having a wave form shown at'D. If the loop antenna 1 be rotated in the opposite direction from the null position, the oscillations present in the output circuits of the electron discharge devices 4 and 5 will be in opposed phase relation and then the combined oscillations will be in the form of the wave shown at E. This wave when passed through the demodulator 6 produces an output current such as is illustrated at curve F. These output currents D or F are then passed through the non-linear resistance 15 which has the peculiar property of causinga direct current to flow when asymmetrical wave shapes are passed through it. The wave at D will produce a direct current in one direction whereas the wave shown at F will produce a direct current in the opposite direction. This current passes through the zero center meter 13 to give an indication that the loop antenna has been turned either to the right or left of the null position. As the demodulator 6 is equipped with an automatic volume control which operates primarily in response to the oscillations received by the nondirective antenna 2, the amplitude of the wave forms C and E supplied to the demodulator 2 are of equal amplitude so as to produce low frequency currents such as D and F of equal amplitude, thereby providing symmetrical indication of the angular rotation of the directive antenna 1 It is to be understood, however, that the demodulator 6 may comprise any suitable receiving circuit equipped with automatic volume control, and including radio and audio frequency amplifiers. A switch 1? serves to incapacitate the oscillator 9 so that the demodulator 6 may be readily tuned, and that communication may be received by use of the antenna. 1 It is also obvious that the arrangement described above may be used as a direction finder without any relation to the remainder of the automatic steering equipment disclosed in Fig; 1. Such a direction finder is suitable for operation on all-types of mobile craft.

Referring again to Fig. 1- of the drawings, a magnetic compass is provided which may be of any suitable construction and which in the form shown comprises a pair of pole'pieces 18 and an armature 19," the latter of which is rotatedby means, not shown, in the field established "by the pole pieces 18. when the pole pieces 18 are at right angles to the direction of the earths mag netic field, no voltage is set up across the armature 19. When, however, the craft turns either to the right or to the left, then voltage is induced in the armature winding having a polarity dependent upon the direction of turn of the craft. Means'are provided whereby the compass tends automatically to maintain itself in such a position directly across the armature of the compass and which is arranged through electron discharge devices 21 and 22 and magnetic clutching mechranged on the shaft with a gear 26 which in turn meshes with a gear 27. The gear 27 is arranged on a common shaft with worm 28 which cooperates with a worm wheel 29 and thereby causes rotation of the worm wheel 29 in one direction or the other, dependent upon the voltage induced across the armature 19. This worm wheel is connected directly with the pole pieces of the magnetic compass whereby in response to any voltage set up across the armature the pole pieces are revolved in such a direction that this voltage is reduced to zero.

The gear 24 is arranged on a shaft which extends to bevel gears connected to the clutching mechanism 23 which carries two oppositely disposed discs 30 and 31 at the opposite ends thereof. These discs are arranged for rotation with a shaft connected to the motor 34 but are movable longitudinally thereof. These discs comprise friction clutching members each of which cooperates with an opposite clutching member 32, 33. These latter clutching membersare mounted loosely upon the shaft of the motor 34 and provide for the rotation of the bevel gear 24 in opposite directions by means of bevel gears attached to the clutch members 32, 33. This clutching mech-\ anism, however, may be of any suitable'construction, and may, for example, be of the type shown in United States Patent No. 1,169,937, issued February 1, 1916, to M. J. Dikeman.

The rotatable clutching members 32 ancl 33 have suitable coils woundthereon, each coil being connected in the anode circuit of one of the discharge devices 21 and 22 whereby these coils are selectively energized in response to operation of the relay 20. The grids of the discharge devices 21 and 22 are each connected to the cathode through a resistance and capacitance combination 35 and 36 respectively and a common source of bias potential 37. This source of bias potential is of such a value that normally no current flows in the anode circuit of the discharge devices. Each grid, however, is also connected through a suitable low resistance 38, 39 respectively, to the opposite contacts of the polarized relay 20, the movable contact of which is connected to the cathodes of the discharge'devices. Thus, upon movement of the armature of relay 20 in either direction the voltage upon the grids of the respective vacuum tubes is sufliciently diminished to cause current to flow in the anode circuit, therebyenergizing the respective clutching members 32, 33. The energized clutch member then attracts the cooperating clutch member 31, .32, which in turn causes rotation of the bevel gear 24 and hence actuation of the pole 5 pieces 18 in a direction such that the voltage across the armature is reduced and the relay 20. therefore, returns to its neutral position.

Thus, the magnetic compass tends to maintain itself in an east-west position; that is, at such an angle with reference to the lines of magnetic force that no voltage is produced across.

the armature. It will, of course, be understood that other means may be employed whereby the compass is adjusted to zero voltage when the pole pieces deviate from the east-west position, such. for example as means for shifting the brushes about the armature. 1

For the purpose of correcting certain errors which occur in the operation of the compass due to the effect of the vertical component of the earth's magnetic field upon turning of the craft,

5 a gyroscopic device 40, which I have indicated by a circle G, is provided and arranged to produce an electromotive force on resistance 41 connected in series with the armature, sufllcient to compensate for this error. Since this gyroscopic device is well known in the art, having been fully described by Dr.- J. D. Tear and E. J. Lawton in the General Electric Review for April, 1931, no description of it will be made here.

While the craft may be steered, by the means already described, along a course determined by a predetermined angle with reference to the direction of the earth's magnetic field, in accordance with my invention this equipment is combined with a radio direction-finding device whereby the craft is not only maintained on a course having a predetermined angle with the direction of the earths magneticfield, but is also maintained upon a course leading to its destination nothwithstanding any forces, such as that produced by wind, which tend to cause the craft to drift from its course.

Means are provided on the craft whereby the output currents passing through the meter 13 control the rotation of the rudder, dependent upon the flow of current through the meter.

This means comprises a resistor 42 and a polarized relay 43 connected in series with the meter 13. The rudder of the craft is indicated in the drawings at 44 and is arranged to be operated through a suitable magnetic clutch arrangement 45 similar to the clutch arrangement 23. This clutching mechanism is controlled by a pair of electron discharge devices 46 and 47 and the polarized relay 43, all in a manner which has previously been described in connection with vacuum tubes 21 and 22 and polarized relay 20.

As thus arranged, if the position of the loop 1 is such that the direction of current through the resistor 42 and the relay 43 is in a. certain direction, then the armature of relay 43 will be operated into engagement with one of its opposite contacts, thereby causing energization of the respective clutch magnet and operation of the rudder 44 in a corresponding direction. If the loop 1 is in such position that the direction of current through the resistor 42 and the relay 43 is reversed, then the armature of relay 43 is operated into engagement with its opposite contact, thereby energizing the opposite magnet of the clutch 45 and causing actuation of the rudder 44 in the opposite direction. The rudder 44 is operated by the clutch mechanism 45 through a pair of gears 48 and 49 and a cord and pulley arrangement '50, the pulley being arranged on the shaft with gear 49.

The shaft of gear 49 is provided with a contact 51 which moves over a circular potentiometer 52 the opposite terminals of which are connected to opposite power supply conductors 53. A re- 5 sistor 54 having a midpoint tap is connected to opposite terminals of the power supply conductors 53 and across the gyroscope 40. A bridge arrangement of resistor 42, relay 43 and resistors 55 and 56 is connected so that opposite points 70 of the bridge are connected to the midpoint of resistor 54 and the contact 51 of potentiometer 52. The point of the bridge between relay 43 and resistor 42 is connected to the midpoint of resistor 54, whereas the point between resistors 75 55 and 56 is connected to the contact 51. This arrangement of elements constitutes a follow-up arrangement which operates to prevent the rudder 44 from over-steering. When the rudder 44 is in a neutral position no voltage is supplied across the bridge by potentiometer 52 and hence 5 relay 43 is not affected. However, upon any movement of the rudder 44 in response to the operation of relay 43 which has been initiated by the current flowing through meter 13, a potential is supplied by the potentiometer 52 to the bridge circuit 42, 43, 55 and 56, which will have a polarity tending to neutralize the voltage which initiated the operation of relay 43.

The resistance 57, which is connected in series with the midpoint between the resistors 55 and 56, is also utilized to introduce a voltage into this circuit in response to operation of the rudder 44. Thus, for example, on the shaft of gear 58 is frictionally mounted a contact 59 which cooperates with two oppositely disposed contacts 60 and 61. The manner in which contact 59 is arranged upon the shaft of gear 58 is such that if the shaft rotates in one direction, the contact 59 rotates in the corresponding direction until it engages the respective stationary contact, after which it remains in that position until rotation of the shaft ceases, when it returns to its neutral position. Contacts 60 and 61 are connected respectively to conductors 53 which are of opposite polarity. The contact 59 is connected to a terminal between the resistors 55 and 56 whereby a voltage is set up across the resistors having a polarity dependent upon the direction of movement of the rudder 44. This voltage operates to oppose the voltage across resistor 42 and relay 43 to produce certain effects which will later be described.

The loop antenna 1 is interconnected with the pole pieces of the magnetic compass through a suitable differential gear arrangement, and is thereby arranged to be maintained automatically at a predetermined angle with reference to the pole pieces of the compass independently of movement of the craft. This differential mechanism is arranged between two gears 62 and 63 which are loosely mounted upon a shaft 64. The gear 62 cooperates with a gear 65 which serves to control the position of the loop through a worm 66 and worm wheel 67. The gear 63 cooperates with a gear 27 which, as previously described, 00 operates with the gear 26 and serves to drive the worm 28 and worm gear 29, thereby to position the pole pieces of the magnetic compass. The differential comprises oppositely arranged bevel gears 68 which are made integral respectively to the gears 63 and 62 and between which are disposed additional bevel gears 69, these latter bevel gears being arranged for rotation about the shaft 70 at right angles to the shaft 64 and which is connected to the shaft 64 to cause rotation thereof about its own axis. The shaft 64 is also rotated by means of gears 71 and 72 which may be manually operated by means of a course setting device 73. An indicating device 74 is also operated by gear 75 which cooperates with the gear 63.

As thus arranged, the operation of the system is as follows: Letus assume that the craft, which may be an air-craft for example, is at a position indicated Start in Fig. 3, and that it desires "0 to fly to a point indicated Destination in this figure. Also, let us assume that in proximity to the destination of the air-craft is a. radio transmitting system, which I have indicated by a simple antenna 76. This radiating system may be 75 finding system, or homing device, or by the me- 1 ter 13 of the direction finding device of the present disclosure, if it be assumed that no automatic drift compensation is employed, the actual course taken by the craft will be dependent upon the direction and velocity of thewind. 7 Thus, for example, ifwe assume wind blowing from the right, as indicated by the arrow bearing the legend Wind in the drawings, the craft will take a curved course, which I have indicated by the dotted line 78, although it may be continuously headed toward the destination. Due to the wind it drifts bodily to the left without changing the direction of its fore and "aft line. When automatically steered by the equipment described, however, and in accordance .with. my invention, the fore and aft lineof' the craft is caused to vary in such a way that the craft actually heads into the wind at an angle sufiicient to overcome the effect of drift and to maintain itself on the true course. Thus, for example, the craft may take a position with reference to the course such as indicated at 79, where the fore and aft line of the craft is shown at,a substantial angle to the true course and the craft is indicated'as heading intothe wind, but following the true course. The craft,therefore, tends to fly more or less sidewise, or to crab along the course.

In adjusting the equipment for automatic steering, the pilot first determines the angle between the direction of the earth's magnetic field,

are in the east-west position and no voltage is' produced across the armature. The loop antenna 1 is at right angles with the direction of propagation of the received waves, with the result that no direct current is produced in the output circuit of the demodulator 6.' Let us assume, however, that due to the wind blowing from the right, as indicated by the arrow, the craft drifts bodily toward the left. Since the direction of the fore and aft line is unchanged, the compass remains satisfied- The loop, however, is no longer at right angles to the direction of the received waves. Accordingly, a current appears in the output circuit of the demodulator 6. This current causes energization of polarized, relay 43 which actuates its armature for example to the right, thereby, through vacuum tube 4'7, causing energization of the upper magnet of the clutching mechanism 45. The rudder is vthus operated through gears 48 and 49 and the cord and pulley arrangement 50 in a direction tending to steer the craft toward the course. Upon any movement of r the rudder, however, the contact 51 cooperating with potentiometer 52 is correspondingly operated and supplies voltage back into the circuit of the winding of polarized relay 43 in a direction to cause deenergization of that relay. Also, simultaneously with the movement of the rudder the craft starts to turn into a position such as that indicated at 80in Fig. 3. When this occurs, however, the poles of the magnetic compass are moved out-oi. the east-west position, with the result that a certain voltage is set up across the armature, this voltage energizing polarized relay 20, thereby causing actuation of its armature, for example, toward the right. This in turn, through action of the discharge device 22, energizes the left magnet of the clutching mechanism 33, thereby causing actuation of the gears 24, 25, 26, 27, worm 28, and warm wheel 29, which causes the poles of the compass to move back into the east-west position. At the same time that this occurs, however, gears 63 and '75 are actuated and produce a corresponding indication on the dial 74. Since the shaft 64 is held stationary by the course setting device 73, gear 62 is rotated through action of gear 69, thereby causing actuation of gear 65 and of the ,worm 66 and gear 6'7 which in turn causes the loop to be so actuated that the angle between the loop and the poles of the magnetic compass is maintained constant.

Upon any turning of the rudder in response to the operation of the relay 43, contact 59 is brought into engagement either with contact 60 or 61, thereby also supplying a voltage into the circuit of resistances. 42, and 56, having a polarity tending to cause deenergization of the relay 43.

It will appear, however, that before the voltage due to operation of contact -or 61 is supplied back into the circuit of relay 43 sufiicient to cause deenergization of that relay, the craft must necessarily have turned through a certain angle. This angle may be sufficient to cause the craft to head into the wind sufliciently to maintain itself on the course. If it is not, however, the loop antenna will remain unsatisfied, with the result that the cycle of operations is repeated and the craft is given a further turn' with respect to the course, while the com'pass maintains itself in the east-west position and the loop at the constant angle with respect thereto. The efiectof contact 59 is to lessen the duration of the successive movements of the craft, thereby causing it to hitch itself through successive increments of angular movement until it occupies a positionsuch that it follows the course to its destination.

If the wind lessens or changes its direction, the relays 20 and 43 are operated-in the opposite direction thereby to correspondingly adjust the rudder to maintain the fore and aft line of the craft at a proper angle wvith respect to the course.

The actual movement of the craft under con--- trol of the equipment occurs in rapid increments which are so small as to avoid any noticeable step by step effect, the equipment tending to maneuver the craft along the course in a. manner just to overcome the tendency to drift and in a smooth and satisfactory way.

The indicating device 74 indicates the angle of the ship with reference to north,-and the device {73 indicates the angle of the course with reference to north, i. e., the original course setting. The difierence between the indications of these two devices therefore indicates the angle of the ship.with reference to the course, i. e., the angle of drift.

If desired at any time, as in case of .absence of drift, the craft may be automatically steered by the compass alone. For this purpose double throw switch 81 is provided in the connection between the compass and the polarized relay 20, and switch 82 is provided in the output circuit of the demodulator 6. By operating switch 81 to the left and opening switch 82, the steering engine is disconnected from the radio equipment and is connected directly to the output from the compass. In this way the craft is steered entirely by compass control.

- The craft may be steered by radio alone by opening the switch 83 which disables electron discharge devices 21 and 22. By opening switches 83 and 84 electron discharge devices 21, 22, 46 and 47 are disabled, so that only the indicator 13 is operative and steering of the craft may be done manually in accordance with the visual indications of the meter 13.

While I have shown a particular embodiment of my invention, it will of course be understood that I do not wish to be limited thereto, since many modifications, both in the circuit arrangement and in the instrumentalities employed, may

be made. I contemplate by the appended claims to cover any such modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States, is,-

1. In a radio direction finder, the combination of directive and non-directive antenna, means for modulating oscillations received by one of said antenna, means for combining said modulated oscillations with oscillations received by the other of said antenna, means for producing currents having distinctive wave shapes in response to said combined oscillations, said wave shapes being controlled by the orientation of said directive antenna with respect to the direction of propagation of waves received thereon and means responsive to said wave shapes for producing a direct current variable in polarity in accordance with the position or said directive antenna.

2. A direction-finding system including a directive antenna, a non-directive antenna, means for asymmetrically modulating oscillations received from one of said antenna, means for combining and demodulating said modulated oscillations and oscillations received from said other antenna, and means including a non-linear resistor responsive to said demodulated oscillations for producing a direct current through said resistor having a polaritydependent upon the direction of orientation of said directive antenna with respect to the direction of propagation of received waves.

3. A direction finder including a directive an-' tenna, a non-directive antenna, means for asymmetrically modulating energy received by one of said antenna, means for combining and demodulating the energy received by both of said an-.

tenna, and means for supplying the demodulation products to a circuit including a polarity responsive device and a bilaterally conducting non-linear resistance connected in series with each other and with the supplied demodulation products whereby a. unidirectional current flows in said non-linear resistance and polarity responsive device having a polarity dependent upon the orientation of said directive antenna with respect to the direction of propagation of received waves.

4. A radio compass system including a directive antenna for receiving energy from a transmitter, means for asymmetrically modulating energy received. by said directive antenna from said transmitter, a source of high frequency oscillations, means for combining and demodulating said modulated energy and energy from said source of oscillations, a non-linear bilaterally conducting resistor and an indicator connected in series for receiving said demodulated energy whereby said non-linear resistor and said indicator cooperate to indicate the presence of an angle between the direction of said directive antenna and a plane normal to the direction of said transmitter.

5. In a direction-finding system, directive and non-directive antenna for receiving energy from a radio transmitter, means for asymmetrically.

into asymmetric currents having a wave form dependent upon the direction of rotation necessary to place said directive antenna in the null position with respect to said transmitter, and means responsive to said asymmetric currents for producing a direct current having a direction determined by the asymmetry of said latter cmrents.

'7. In a direction-finding system, a transmitting station, a receiving station having directive and non-directive antenna for receiving energy from said transmitting station, means for asymmetrically modulating energy from said directive antenna, means for combining said modulated energy with energy from said other antenna to produce distinctive currents in accordance with the direction of rotation necessary to bring said directive antenna into the null position with respect to said transmitter, and means responsive to said distinctive currents for indicating the direction of rotation of said directive antenna.

8. In a radio direction-finding system, directive and non-directive antenna for receiving energy from a radio transmitter, means for asymmetrically modulating energy received from said directive antenna, means for combining and converting said modulated energy and energy from said non-directive antenna to produce asymmetric currents, the asymmetry of said currents being dependent upon the direction of rotation necessary to bring said directive antenna into the null position with respect to said transmitter, and means including a substantially instantaneous responsive non-linear resistor for producing a response to the asymmetry of said latter currents.

9. In combination, a directive antenna, a bilaterally conducting non-linear resistance, and means to cause a unidirectional current to flow in said resistance having a polarity dependent upon the orientation of said antenna with respect to the direction of propagation of received waves.

tation of said antenna with respect to the direction of propagation of received waves, and unidito produce a wave having either of two asym-' metrical wave forms dependent upon the orientation of said antenna with respect to the direction of propagation of received waves, and means se- 10 lectively responsive to said wave forms.

12. In combination a directive antenna, means to produce a wave having either of two asymmetrical wave forms dependent upon the orientation of said antenna with respect to the direction of propagation of received waves, and means selectively responsive to said wave forms, said means comprising a circuit including a polarity responsive device and a non-linear bilaterally conducting resistance, and means to supply waves having said asymmetrical .wave forms to said circuit.

HOWARD I. BECKER.

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