US3020547A - Arrangement for radio direction finding - Google Patents

Description

Feb. 6, 1962 CARL-ERIK GRANQVIST 3,020,547

ARRANGEMENT FOR RADIO DIRECTION FINDING Filed June 24, 1957 I In I 15 ATTORNEYS with a synchronous generator.

the relations in a transformer.

United States Patent Oificc 3,02%,547 Patented Feb. 6, 1962 3,020,547 ARRANGEMENT F013 RADIO DIRECTION FINDDIG Carl-Erik Granqvist, Lidingo, Sweden, assignor to Svenska Alttieholaget Gasaccumulator, Lidingo, Sweden, a

corporation of Sweden Filed June 24, 1957, Ser. No. 667,317 Claims priority, application Sweden Aug. 2, 1956 12 Claims. (Cl. 343114) The traditional way of finding the direction by radio is to use a strongly directional antenna system, for instance a frame antenna, which is either actually turned to observe the maximum or minimum voltage, or the turning of which is instead simulated by connecting a pair of mutually crossing antennas to a radio goniometer, the reading coil of which is turned in a corresponding way. Both of these arrangements, however, suffer from a disadvantage often observed. In turnable frame antennas, which are controlled by hand, it has been usual to limit the total turning angle of the frame to a little more than one turn. It has then been possible to connect the frame antenna with the receiver by means of a flexible conductor without slip contacts. However, it has proved, that .such a small turning is very often insufficient for a quick and easy handing, and one has in some cases by a specially expensive arrangement increased the total turning angle of the frame up to two turns, but thereby an expensive and complicated stop device has been necessary, and the flexible conduits also become more complicated and expensive. Finally this arrangement cause that part of the conductor has to hang down freely, whereby it has been sensitive to mechanical disturbances. Even the best ground mantled coaxial cables are to a certain degree sensible to electro-magnetic disturbances, and the longer the conductor is, the stronger these disturbances will be. In direction finding with a radio goniometer one has always had to use slip rings for transferring the received signal volt-age to the receiver, and the same has been the case in automatic direction finding, which requires as well known, continuously rotating direction finding antennas. Y

Slip ring contacts, however, always cause disturbances due to the weak currents to be transferred, the so called contact noise.

In order to avoid the above disadvantages and to provide an arrangement for a direction finding antenna, in which neither flexible conductors, nor slip ring contacts are required, it has been proposed to arrange the direction finding antenna for electro-magnetic waves in such a way, that it is influenced by the magnetic field. It contains for this purpose a turnable so called Z-armature.

of a material with high conductive property for this field.

In induction compasses one has already used Z-armatures, but these have been kept in rota-tion with a very high speed, wherebythey induced a voltage dependent upon the horizontal component of the earth-magnetical .field. in this case, the magnetical field is uni-directional,

and the Z--armature rotates in this field to create an alternating voltage. Such an arrangement can be compared In the arrangement according to the invention,on the other hand, a Z-armature is used in a way, which could better be compared with The armature is normally not in rotation, but can of course be turned into different positions, representing dififerent directions of the input field. This, however, is an alternating field per se,

and in the winding about the stem of the Z-armature therefore an electric voltage will be created the same way as the voltage in the secondary winding of a transformer, when the magnetic field in its armature or core is made object of a'periodical variation. The state of'voltage thus occurring in the winding of the Z-anna-ture then will form a measure of the direction of the input field, or with other words: The Z-armature can be used as an antenna with a strong directional action.

Tests have proved that the signal intensity achieved in this way is fully sufficient for direction finding purposes, and that this signal intensity in no way needs to be weaker than the field intensity in a normal frame antenna device, measurcd as the output voltage from the antenna. 011 the other hand, one has fully avoided slip ring contacts as well as long freely hanging conductors, and thereby also all of the disturbances occurring in all frame antenna systems, and therefore the received signal will be essentially more pure and easy to understand. 7

The said earlier known arrangement, however, is not perfect, because it is sensible to input waves with horizontal polarization. It should be remembered, that the force lines of the input field as a rule contain not only an horizontal component but also a distinct vertical component.

For avoiding the abovementioned disadvangages, a circul-ar series of directional poles are provided around the Z-armature, and said directional poles are divided in such a way, that a field division is obtained, which is at least approximately sinusoidal.

The invention will be further described below in connection with the attached drawing, which shows some forms of execution of the invention.

In the drawings:

FIG. 1 is a diagrammatic view of an arrangement of an embodiment of the prior art with reference tothe present invention;

FIG. 2 is a diagramma 'c and vertical view of an embodiment of the present invention;

FIG. 3 is a diagrammatic and horizontal view of a modified embodiment of FIG. 2; and

FIG. 4 is an arrangement of the present invention including a device for use in side distinction in accordance with the invention.

In FIG. 1 a Z-armature is indicated by 10, said armature being of the kind which is known from the induction compass .technics. The armature 10 is turnable in about the same way as a normal frame antenna, about an axis 11, which in this case coincides with the centre line of the stem 12 of the Z-armature. This stem is surrounded by a winding 13, which is connected with the direction finding receiver 14, shown in block diagram, and thereby with the loudspeaker 15. On the shaft 11 a scale disc 16 with a reading mark 17 is provided. This can for instance be provided with all kinds of different means for improving the readings, known from usual direction finding systems with frame antenna, such as for instance a vernier for correcting the reading angle and so on. It should, however, be observed that even if here and in the following the arrangement has been described in connection with a system for manual direction finding, the invention is of course also possible to use in automatic direction finding, where it will get its most essential advantages.

The arrangement according to FIG. 1 functions in the following way:

When the Z-armature is directed with its one leg onto the transmitting radio beacon and with its other leg in the exactly opposite direction, the armature will receive a magnetic field, which is conducted through the winding 13 With the same action as if a frame antenna had been arranged with its plane exactly perpendicular to the direction of the horizontal component of the input wave. In a corresponding way, the arrangement according to FIG. 1 acts when the legs of the Z-armature are directed perpendicularly to the direction of the horizontal component of the input wave in substantially the same way as if a frame antenna had been set with its level in the direction of the input wave. The characteristics will be almost the same as that for a frame antenna. One can consequently turn the Z-armature in the same way as one used to do in traditional systems with a frame antenna, and listen to the field intensity in the form of the sound intensity on an interference tone in the loudspeaker 15. Suitably the direction finding should be made on a minimum of received signal intensity in this case as in a frame antenna system.

According to the invention the influence from the vertical component is avoided by using a rather small 2- armature and combining this with fixed magnet conductors provided at the outside of it. One such arrangement is shown in FIGS. 2 and 3. In this arrangement the Z-arrnature is indicated 23 and the coil 24. These two parts are in other respects similarly arranged as in the device according to FIG. 1. This part of the magnet antenna, however, is surrounded by a screen 25, which is sutficiently well conductive for preventing the electromagnetic field and especially its vertical component to run freely through the interior of the screen. In order to conduct the field in controlled form within the space inside the screen, a slot 26 or a series of openings is provided in the screen 25, and through these openings a number of directional magnets or directional poles 27 extend into the interior of the screened space. The directional magnets or directional poles are of course made of a very soft iron material or other good magnetically conductive material, such as ferrite, which is also the case with the Zarmature, around which conventional coils may be wound to induce a magnetic field when energized.

It is now obvious that one should have at least four such directional poles, but also, that the division of the field with the rotation of the Z-arm-ature would not be especially well sinusoidal, if only four poles are used. In the arrangement shown, twelve such poles have been provided, grouped with three poles in each cardinal direction, mutually separated by an angle of 22.5 and with a spacing, corresponding to one directional pole in the directions, corresponding to the inter-cardinal directions. When in this connection it is spoken about cardinal directions this way of expression does of course not mean the geographical directions, but the longitudinal ship direction and the cross ship direction of the vessel, or starboard or port abaft and before the beam, respectively. Further the poles of the Z-armature have been widened to the form of a couple of circular sectors 28, 29, comprising a circular bow at their outer circumference of 45' as measured from the cent-re of the axis of the shaft 30 running through the stem of the Z-armature. This arrangement has proved to give a very closely and fully satisfactory accurate sinusoidal division of the field during the turning of the magnetic antenna, but it is obvious that also other forms of the directional magnets and the armature poles may be used.

As is the case in magnetic compasses, the magnetic antenna of the abovementioned kind should also be compensated for with regard to the iron of the vessel. This compensation may take place in a plurality of different ways.

One way is to provide each of the directional magnets displaceable in its own longitudinal direction, so that it can be adjusted to a greater or smaller distance from the poles 28, 29 or the Z-armature. Another way which may be used alone or in combination with the first-mentioned way, is to use a set of directional poles of assorted lengths and choosing directional poles of a suitable length in each separate position. For instance a good result has been obtained by using in one single magnetic compass directional poles of four different lengths, which may be exchanged for one another until the required accuracy of the compensation was achieved.

A third way of providing compensation means for the magnetic directional antenna according to the invention is to provide pole shoes 31, 32, 33, 34 in a way which. is apparent from FIG. 3. These pole shoes should be displaceable perpendicularly to their own longitudinal direction, closer or more far away from the adjacent ends of the directional poles 27. Possibly one or more of the pole shoes may be completely removed.

Finally, for compensating the magnetic antenna, one can use one or more magnetic shunts, provided in a way, which is apparent from FIG. 2, where one such magnetic shunt is indicated at 35, and another at 36. The shunts should be displacea'ble separately in the axial direction of the Z-armature and further they should be turnable separately.

In traditional frame antennas means are also used for determining the side field, that means, for deciding, from which side of the level of the frame antenna side detection may take place. As far as regards this detail the invention is based upon the same principle, which has also been made in goniometer direction finding. Thereby as well-known, an extra winding is used on the rotor part of the goniometer, said winding being orientated from the normal finding direction. The side detection then takes place in such a way, that one add or subtracts, respectively, the voltage induced in the side detection line, with the voltage, obtained from an auxiliary an tenna, but turned in phase by 90.

Analogous with this known arrangement, in the arrangement according to FIG. 4 a magnetic antenna consisting of the Z-armature 28, 29, the coil 24, and the directional pole 27, is combined on the same shaft 30 with a smaller magnetic antenna, consisting of a Z-armature 3'7, with a coil 38 and a series of directional poles 39, 40. The two Z-armatures 28, 29 and 37, respectively, are, as evident from the drawing figure turned relative to each other by an angle of 90".

Of course, this invention is not limited to the specific forms of execution described above and shown in the drawing, but different modifications may occur Within the scope of the invention.

What is claimed is:

1. An arrangement for radio direction finding comprising a magnetic antenna having a magnetic core in the form of a Z-armature, said antenna being rotatable about the axis of the stern of said armature, a coil around said core, and a plurality of elongated magnetic conductors radially disposed about said armature in an arrangement providing a sinusoidal field distribution; whereby when said antenna is rotated the field intensity through said core will vary substantially sinusoidally with the angle of rotation.

2. An arrangement according to claim 1 wherein said elongated magnetic conductors are disposed in groups at each of the four cardinal points.

3. An arrangement according to claim 2 wherein each of said groups is composed of three of said conductors displaced at an angular difference of 22.5 degrees.

4. An arrangement according to claim 1 wherein the poles of said armature are wider at their outer edge.

5. An arrangement according to claim 4 wherein said wider edge encompasses a circular arc of 45 degrees.

6. An arrangement according to claim 1 wherein said elongated magnetic conductors are axially displaceable whereby said antenna may be compensated for iron present in the carrier.

7. An arrangement according to claim 1 wherein said elongated magnetic conductors are of varying lengths to compensate said antenna for iron present in the carrier.

8. An arrangement according to claim 1 including magnetic shunts to compensate said antenna for iron present in the carrier.

9. An arrangement according to claim 8 wherein said magnetic shunts are displaceable in a direction parallel to the axis of said core.

10. .An arrangement according to claim 2 including magnetic pole shoes at the outer end of each of said groups of magnetic conductors.

11. An arrangement according to claim 10 wherein said magnetic pole shoes are displaceable away from the adjacent ends of said groups of magnetic conductors.

12. An arrangement according to claim 1 including a second magnetic antenna having a magnetic core in the form of a Z-armature, said second antenna being rotatable about the same aXis as said first antenna, the poles of said second armature being displaced 90 degrees rela- 10 tive to the poles of said first armature, a coil around the core of said second antenna, and a plurality of elongated magnetic conductors radially disposed about said second armature.

References Cited in the tile of this patent UNITED STATES PATENTS- 2,740,113 Hemphill Mar. 27, 1956 2,755,468 Mountjoy July 17, 1956 2,807,801 Hemphill et al Sept. 24, 1957 2,807,802 Hemphill et a1 Sept. 24, 1957 2,870,442 Polydorofi J an. 20, 1959 2,93 1,03 7

Granqvist Mar. 29, 1960

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