US2820219A - Wireless direction-finder - Google Patents

Description

Tm. 14,- 1958 SHIGEO sATo 2,820,219

- WIRELESS DIRECTION-FINDER Filed July 15, 1953 V I 2 Sheets-Sheet 1 J0 saw-awe INVENTOR.

/ ATTORNEYS Jan. 14, 1958 sHl'e'EdsATo; 2,820,219

WIRELESS-DIRECTION-FINDER Filed July 13, 1953 2 Sheets-Sheet z 32 W0 roe INVENTOR.

ATTORNEYS.

Patented Jan. 14, 1953 2,820,219 WIRELESS DIRECTION-FINDER Shigeo Sato, Tokyo-to, Japan Application July 13, 1953, Serial No. 367,569 7 Claims. (Cl. 343-118) This invention relates to an improved wireless direction-finder.

In the usual wireless direction-finder provided with a cathode-ray tube and capable of indicating directly all directions of the electric wave received, it is customary to indicate the intensity and direction of the electric wave on the cathode-ray tube by rotating the directional antenna at a proper speed, making the tube describe a circular or ring-shaped fluorescent image at a speed synchronous to said rotation and modulating the image by the wave obtained by amplifying the electric wave received.

The method for describing a circular or ring-shaped fluorescent image on the cathode-ray tube may comprise transforming a single phase A. C. voltage into two phase A. C. voltage by means of a phase converter and supplying the output voltage of said converter to the vertical and horizontal deflecting plates or deflecting coils. The method as described above, however, has the disadvantagesthat it is very difficult to make a phase converter having good frequency characteristics and to obtain sufficient two phase power, the latter defect being due to high impedance.

On the other hand, it is well-known to rotate the deflecting coils of the cathode-ray tube at a speed synchronous to the rotation of the directional antenna by means of a selsyn motor. This system, however, has the disadvantages that the image is distorted due to nonsynchronism and that vibration and noises occur in the apparatus which drives the deflecting coils.

It has been proposed to couple the polyphase A. C. generator directly with the directional antenna to' eliminate the defects as described above. According to such method, however, the generated voltage is constant and brightness modulation of the cathode-ray tube is carried out only by the variation of the output voltage in the antenna, so that the fluorescent image corresponding to the minimum sensibility of the directional antenna is very indistinct resulting in very difiiicult and inaccurate observation.

The object of this invention, therefore, is to provide a direction-finder which is relatively simple in construction and accurate in operation and has no defects as described above.

The above object and other objects of this invention are accomplished by a system which comprises a directional input device and a rotary type polyphase A. C. generator capable of generating polyphase voltages which vary in relation to the output voltage of the input device, the polyphase voltages being used as the deflectingelements of the cathode-ray tube and the input device and generator being revolved synchronously with respect to each other under their directly coupling condition.

This invention will be more clearly understood by reference to the following detailed description taken in conlug drawings, wherein:

Fig. 1 shows a schematic arrangement of an example of this invention.

Fig. 2 is a connection diagram of an example of a rotary type two phase A. C. generator to be used in the JllCCtlOIl-fiIlClBI' of this invention.

Fig. 3 is a connection diagram of an example of the exciting circuit for feeding the two phase A. C. generator illustrated in Fig. 2.

Fig. 4 is a schematic view of a fluorescent image obtained by the apparatus illustrated in Fig. 1.

Fig. 5 shows a schematic arrangement of another example of this invention.

Fig. 6 is a schematic view of a fluorescent image obtained by the apparatus illustrated in Fig. 5.

Referring to the example illustrated in Fig. l, the directional input device 1 consists of a loop antenna, Ad-

.cock type antenna or poniometer which is coupled directly with two phase A. C. generator 2. The motor 3 is arranged to rotate synchronously, with both parts 1 and 2, at a speed of about ten revolutions per second. The generator 2 and cathode-ray tube 4 are connected electrically so that the first phase output of said generator may be supplied to a pair of deflecting plates of tube 4, V

and the second phase output may be supplied to another pair of deflecting plates, the latter pair being positioned perpendicularly to the former pair. A receiver 5 is connected to the output terminals of the directional input device 1 and a Wave detector 6 is connected to the output terminals of the receiver. An oscillator '7 capable of generating an oscillating voltage of about 20 kilocycles per second is connected to the output side of detector 6 so that the output voltage of the oscillator may be superposed to the detected output voltage of said detector, the resultant output voltage being supplied to the two phase A. C. generator 2 after amplification by an amplifier Coupling transformers 9 are inserted in the circuits connecting the generator 2 and the cathode-ray tube 4 to make the impedances in the secondary winding of said generator 2 match with the resultant of the impedances in the deflecting plate circuit of the cathode-ray tube and the connecting wires Ill. Any type and construction of the generator may be adopted if it is a rotary type, because it must be coupled with the directional input device to effectuate the principle of this invention.

For example, a generator similar to the ususal two phase A. C. generator of large capacity may be used, but such type is very complex in construction and is inaccurate in operation due to unbalance of the connecting terminals and due to mutual inductance and stray capacitance in the part of said terminals.

The generator illustrated in Fig. 2, however, is very simple in construction and manufacture and is capable of generating efficiently and accurately a two phase A. C. voltage output.

The two phase A. C. generator illustrated in Fig. 2 consists of a stator A consisting of a circular ring-shaped iron core 11 and an endless winding 12 wound toroidally with a uniform distribution on the core, and a rotor B consisting of an iron core 15 and a winding 16 similar to those of the stator A. Iron cores having a cross sectional surface of any form, for example, rectangular, circular or any other form may be used, but it is preferable to form it from a material such as dust core, which is relatively low in high frequency loss and large in permeability. The stator winding 12 is provided with vertical terminals 13 and horizontal terminals 14, the former being led from two points on a diametrical vertical-line of said winding and the latter being led from two points on a diametrical horizontal-line of said winding. The rotor B ,is supported rotatably in the stator A by a suitable means for example, by holding it between two disks supported rigidly by a rotary shaft, the disks and rotary shaft being omitted. in the drawing.

For the purpose of concentric support of the stator and rotor any other means may be adopted.

The endless winding 16 wound toroidally with a uniform distribution on the rotor iron core is connected to the slip rings 17 at its bisected points as shown in Fig. 2.

In the generator illustrated in Fig. 2, when the rotor is revolved at a constant speed and any A. C. voltage of a suitable high frequency is supplied on the winding 16, then two phase A. C. voltage will occur at the terminals 13 and 14 due to an induction phenomenon between the stator A and the rotor B. The large part of magnetic path of said generator consists of the iron cores 11 and 15 of large permeability and only very little air gap is left between said iron cores, so that the mutual inductance between both windings 12 and 16 becomes very large. For the purpose of increasing said mutual inductance more effectively, it is preferable to wind the windings in the slots of their iron cores. Moreover, the stator and rotor windings of said generator are wound toroidally with a unifrom distribution on their cores under endless condition, so that said generator is very simple in construction and has no unbalanced constructional parts such as the connection ends of the windings, such parts taking no part in voltage induction. Furthermore, there are no large stray inductance and stray capacitance, so that an accurate two phase A. C. voltage will be generated effectively. When the stator winding 12 is wound with a uniform distribution and the rotor winding 16 is wound with a sine distribution, then two phase A. C. voltage of great accuracy will be obtained. In the embodiment of the generator illustrated in Fig. 2, it may be allowable to use the stator and rotor of same size and to fix them concentrically on a rotary shaft side by side instead of the concentric arrangement as indicated in Fig. 2.

Fig. 3 shows an actual connecton diagram of the oscillating circuit capable of generating an exciting voltage to be supplied to the A. C. generator. In the Fig. 3, the voltage e corresponds to the carrier output voltages of the receiver 5 in Fig. 1, for example, to the output voltage of an intermediate frequency which is obtained by demodulating the voltage induced in the directional input device by a superheterodyne receiver. It is provided with a detecting vacuum tube 18, a load 19 and a filter 20. The filter is made so as to eliminate the carrier wave contained in the amplified output voltage of the directional input device and pass only the envelope of the carrier'wave therethrough, the frequency of said envelope corresponding to the fundamental frequency due to rotation of the directional input device.

The exciting voltage 2 of about 20 kilocycles is superposed on the output voltage of the filter 2t) and through transformer 21 and a voltage divider 22. The resultant voltage is supplied to the grid electrode of the vacuum tube amplifier 23. For amplifier 23 it is preferable to use, for example, a 6817 tube, in which the mutual conductance varies suddenly in accordance with the variation of the grid voltage.

In the secondary circuit of the output transformer 24 is connected a condenser C to form a resonant circuit to attenuate the harmonic waves. All parts in the apparatus of Fig. 3 should be designed so that when the output voltage of the receiver is almost zero the output power of the output transformer 24 may becomes maximum and decreases with the increase of the output power of the receiver. For example, the parameters should be selected so that when the voltage of the load 19 decreases below 5 volts due to increase of the output power of the receiver, the mutual conductance of the amplifier 23 (6817 tube) becomes zero, and also the output power of the transformer 24 becomes almost zero.

The operation of the direction-finder as described above will be understood by the following descript on.

The apparatus illustrated in Fig. 1 is provided with a loop antenna (not shown). When a l1ne normal to the surface of said antenna is set to the direction of the line connecting two diagonal points of the rotor winding in the two phase A. C. generator, the direction of the line connecting two diagonal points of the stator winding and the direction of a pair of deflecting plates in the cathode-ray tube are set to the standard direction, for example, to north pole, the first pair of output terminals of the two phase A. C. generator is connected with a pair of deflecting plates in the cathode-ray tube and the second pair of said terminals is connected with another pair of deflecting plates and the antenna is coupled directly with the generator and rotated together with the latter by a synchronous motor at a speed of about ten revolutions per second, then the rotor winding of said generator will be supplied with an exciting voltage of about 20 kilocycles per second and modulated by the output voltage of the directional input device, and in the stator Winding will be induced two phase A. C. voltage corresponding to the modulated voltage, so that a fluorescent image as indicated in Fig. 4 will be seen on the cathoderay tube.

As will be understood from Fig. 4, when the output power of the antenna is zero, the exciting voltage of the generator becomes maximum and the locus thereof takes a form similar to a circle as indicated by broken line 29. However, upon appearance of the output power in the antenna the exciting voltage decreases in inverse proportion to the magnitude of the output power, so that an envelope 25 of leaf-shaped fluorescent image will appear as a locus of maximum deflecting position of electron beam capable of oscillating symmetrical to the center point 26. In the general cathode-ray tube, however, the diameter of electron beam is about 0.5 mm. and the residual fluorescence of electron beam is only about 0.1 second, so that when a wave of about 20 kilocycles is used and the antenna is revolved at a speed of about ten revolutions per second, the striped pattern 27 will be scarcely visible. When the direction of the deflecting plates in the cathode-ray tube is set to the standard direction, it is possible to decide the direction of the electric wave received by the antenna by means of measuring the angle 0 between the peak points 28 of the envelope 25 and said standard direction. The width of the envelope 25 may be decreased by increasing the amplification coefficient of the receiver, and the radius of the locus '29 may be varied by the voltage divider 22 as indicated in Fig. 3.

The apparatus illustrated in Fig. 5 consists of a directional input device 30, a two phase A. C. generator 31, a motor 32, a cathode-ray tube 33, a receiver 34, coupling transformers 35 and a frequency changer 36 including an amplifier and functions similar to the apparatus illustrated in Fig. 1. The frequency changer 36 is of a type which is capable of transforming the carrier wave, which carries the electric wave received by the receiver 34, into an exciting wave sufiiciently strong and stable, the frequency thereof being about 20 kilocycles. Therefore, the output power of the two phase A. C. generator 31, which is supplied with said exciting voltage, becomes zero when the output power of the directional input device 30 is almost zero and on the other hand it becomes an almost constant value when the output power of the directional input device increases up to a value over a certain value. As a result, when any output power of the directional input device 30 occurs due to an incoming electric wave, a circular envelope 37 having a center point 38 will appear in the cathode-ray tube as indicated in Fig. 6. In this example also striped pattern 39 will appear. The pattern as above, however, can "be made invisible by adopting the exciting voltage of about 2t) kilocycles and by rotating the directional input device at a speed of about ten revolutions per second. On the other hand, wedge-shaped gaps 40 will appear at the positions corresponding to zero output of the directional input device, said positions corresponding to the peak points 28 in Fig. 4.

It is possible, therefore, to measure accurately the angle deflected from the standard direction, that is, the emitted direction of the coming electric wave. Moreover, it is possible to make the widths of the gaps 40 very narrow by increasing the amplitude of the output of the frequency changer 36.

In the above examples, a cathode-ray tube provided with deflecting plates is used. However, one provided with deflecting coils may be used with similar excellent results. Furthermore, it is within the scope of this in vention to use any other polyphase A. C. generator, for example, three phase A. C. generator instead of a two phase A. C. generator, but in this case a cathode-ray tube provided with deflecting device corresponding to said polyphase should be adopted to make the operation similar.

As will be clear from the above description, the direction-finder of this invention has advantages in that the construction is relatively simple, and A. C. generator and directional input device do not get out of synchronism because of the rotary type of said generator and of their direct coupling resulting in lack of errors due to distortion of the fluorescent image. Moreover, noises would not occur as in the case of revolution of the deflection coil.

Furthermore, as the voltage induced in the polyphase A. C. generator varies in relation to the output of the direction antenna, the fluorescent image is very clear and observation becomes very easy and accurate.

Since it is obvious that many changes and modifications can be made in the above described details without departing from the nature and spirit of this invention, it is to be understood that this invention is not restricted except as set forth in the appended claims.

I claim:

1. A direction finder comprising, in combination, a directional antenna, a motor connected to said antenna to rotate the same and thereby to sweep its directional pattern, a generator having a ring-shaped stator core and a ring-shaped rotor core, a toroidal exciting winding on one of said cores and a two-phase toroidal output winding on the other of said cores, said cores and windings being inductively related to one another, a direct mechanical connection between said motor and said rotor core and its winding for rotation of the latter synchronously with the rotation of said antenna, a cathode-ray tube indicator provided with orthogonally disposed deflection control elements, circuits connecting the respective control elements to the respective phase outputs of said output winding, a signal receiver connected for energization from said antenna, and means connecting the signal output of said receiver to said exciting winding whereby the twophase output of said generator is controlled in amplitude by the output signal strength of said receiver.

2. A direction finder in accordance with claim 1, said apparatus being arranged so that the amplitude of the two-phase output of said generator decreases with increasing signal strength output of said antenna, to provide a leaf-shaped pattern on said tube having clear maximal points.

3. A direction finder in accordance with claim 1, in which said means comprises: a detector connected to the output of said receiver, an oscillator, and means for superimposing the outputs of said detector and said oscillator upon said exciting winding.

4. A direction finder in accordance with claim 1, in which said means comprises a frequency changer connected between said exciting winding and the output of said receiver.

5. A direction finder in accordance with claim 1, in which said means comprises: a detector connected to the output of said receiver, an oscillator, and means for superimposing the outputs of said detector and said oscillator upon said exciting winding, said oscillator being adjusted relative to the tuning of said receiver to provide a composite signal to said exciting winding which is ap proximately of the value of 20 kilocycles per second.

6. A direction finder in accordance with claim 1, in which one of said toroidal windings has a uniform spatial distribution along its corresponding core, and in which the other of said toroidal windings has a sinusoidal spatial distribution along its core.

7. A direction finder in accordance with claim 1, said apparatus being constructed and arranged so that the output voltage of said generator is substantially zero when the signal output of said antenna is approximately zero, and so that the output voltage approaches a maximum limiting value for increasing values of antenna signal, to provide clear wedge-shaped gaps in the circular image on said tube.

References Cited in the file of this patent UNITED STATES PATENTS 2,403,967 Busignies July 16, 1946 2,409,456 Tolson et al Oct. 15, 1946 2,427,905 Fyler Sept. 23, 1947 2,483,399 Burroughs Oct. 4, 1949 2,485,585 Goldstein Oct. 25, 1949 2,656.536 Lockhart Oct. 20, 1953 FOREIGN PATENTS 894,379 France Mar. 13, 1944 51,645 France Dec. 10, 1942

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