US2153975A - Radio direction finder - Google Patents

Description

April 11, 1939. s. B. SMITH ET AL RADIO DIRECTION-FINDER Filed Feb. 25, 1937 2 Sheets-Sheet l 250 METERS RAD/US mm M A O R 2 INVENTORS SIDNEY B-SMITH B'Y ERNEST GREEN 51m. ATTORNEY April 11, 1939. s. B. SMITH ET AL 2,153,975

RADIO DIRECTION FINDER Filed Feb. 25, 1937 2 Sheets-Sheet 2 INVEFNTORS SIDNEY B. SMITH ERNEST GREEN ATTEJRNEY Patented Apr. 11, 1939 UNITED STATES PATENT OFFHQE RADIO DIRECTION FINDER Application February 25, 1937, Serial No. 127,622 In Great Britain March 26, 1936 7 Claims.

This invention relates to radio direction finding installations and more particularly to directional radio receiving installations of the well known socalled Adcock and similar types.

It is often desired to set up in a given location a plurality of Adcock type directional receiving aerial systems adapted to operate on different wave lengths. For example, it may be required to provide at a given location an Adcock system for receiving frequencies of the order of 330 kilocycles and another Adcock system for receiving very high frequencies of the order of megacycles. As would be expected, it has been found in practice that a single Adcock aerial system cannot satisfactorily be employed for operation at such dissimilar frequencies as those mentioned and when two systems are provided, one for relatively long wave working and the other for short wave working, it has been found that (unless the two aerial systems are spaced well apart) interference occurs, the principal interference effect being that the relatively long wave system introduced distortion or inaccuracies as regards direction finding by the short wave system. This difficulty can be met by spacing the two systems sufficiently far apart, but since any Adcock system must for satisfactory operation be situated in a location such that the immediate surroundings are free from iron structures or other causes of distortion or inaccuracy, the requirement that the two systems be spaced apart involves occupancy of a relatively large and costly land area by the whole installation. For example, consider the case of an installation comprising a long wave system using waves of the order of 330 kilocycles and having vertical aerials or masts about 100 feet high separated by about 200 feet and a short wave system operable at frequencies ranging from about 4 to about 20 megacycles and having short wave aerials about 30 feet high spaced about 20 feet apart. If using known Adcock systems, interference by the long wave system with reception by the short wave system is to be avoided, the centers of the two systems must be spaced apart by 350 meters or thereabouts, and since each system should be in the middle of a fairly clear space of about 250 meters in radius, the total land effectively occupied by the whole installation will be an area about 850 meters long and 500 meters wide. From the point of View of land occupation it would obviously be of great practical advantage if the short wave Adcock system could be located inside the long wave system so that a circular area of land of about 500 meters in diameter would be sufiicient.

The principal object of our invention is to provide an advantageous combination of aerial systems, preferably of the Adcock type and so dimensioned that different portions of the complete arrangement may be operated at different wave lengths Without appreciable interference as between the portions which are adapted for relatively long wave reception and those portions which are adapted for relatively short wave reception.

Other objects and advantages of our invention will be made apparent in the description to follow where this description is accompanied by drawings including the following figures:

Figures 1 and 2 show concentric aerial systems including long and short wave aerials;

Fig. 3 shows a concentric aerial system in relation to the ground area required to be free from interference structures when such a system is used for direction finding purposes;

Fig. 4 shows two aerial systems arranged eccentrically, and, therefore, requiring more interference-free ground area than is needed for the arrangement of Fig. 3;

Fig. 5 shows schematically certain details of a preferred long wave aerial system for carrying out our invention;

Figs. 6 and '7 show two different, although very simple, modifications of our long wave aerial system;

Fig. 8 shows a further modification embodying a symmetric array of energy collectors having a solenoid formation; and,

Fig. 9 shows a small portion of one of the solenoids as more schematically represented in either of Figs. 5, 6 or 8. Fig. 9, therefore, is provided for better illustrating certain preferred details of structure.

Referring first to Figs. 1 and 2, it will be seen that Fig. 1 is a schematic elevation, while Fig. 2 is a plan view of a symmetric array of vertical aerials.

Al represents the aerials of the long wave system, A2 the aerials of the short wave system and Ft are feeders for the long wave system. If an arrangement like that of Figs. 1 and 2 could be adopted with satisfactory results, there would be obvious economy of land occupation as compared to a system of similar dimensions, but with the short wave system outside and well spaced from the long wave system. The dimensions marked on Figs. 1 and 2 correspond with those already mentioned and with these dimensions the system of Figs. 1 and 2 would require only a clear space of land of about 250 meters radius with the system in the middle. This is shown in the accompanying Fig. 3 which should be compared with the accompanying Fig. 4 which shows the much larger land area required when the short and long wave systems are spaced apart.

Experiment indicates that the principal cause of interference with directional reception by a short wave Adcock or similar system when a long wave Adcock or similar system is in the vicinity thereof, is that standing Waves of short wave length are apt to occur in the long Wave aerials so that they re-radiate short wave energy. The present invention achieves its object by so constructing or arranging the long wave aerials that this action is substantially prevented.

There are two main methods of carrying the invention into effect, and these methods may be used either singly or together. In one of these methods each long wave aerial is loaded with or consists of a series of loading coils, successive coils from top to bottom of the aerial being in opposite sense. In the other method each long wave aerial is terminated by an impedance network which substantially matches the surge impedance and comprises a limb earthed at one end and offering very little impedance to short wave energy.

In one way of carrying out the invention. a direction finding installation. comprises two Adcock aerial systems arranged as shown in Figs. 1, 2 and 3,, one adapted to operate on relatively long waves: and the other on. relatively short waves. A short wave system consists, as shown, of four Vertical aerials A2 arranged at the corners of a square, and. the long wave system consists of four more vertical aerials Al arranged at the corners of another, much larger square, the sides of which are parallel to the sides of the first mentioned square. The necessary feeders from the aerials of the long wave system are arranged radially and lead towards the center of the whole system. Only the feeders Fl for the long wave system are indicated (see Fig. 2). Each long wave aerial which is shown merely as a line in the schematic Fig. 1 is, however, constituted, as shown in the accompanying Fig. 5, by a plurality of ordinary aerial lengths a joined together in series by loading coils or chokes L, successive loading coils or chokes being connected or wound in opposite sense. These loading coils or chokes serve to load each aerial so that standing waves of wave length corresponding to that of the short wave system will be of very small magnitude. The said loading coils or chokes: which are, of course, in effect distributed inductances, may consist of coils wound upon suitable insulators of small diameter, and their method of connection prevents the occurrence of circulating currents in the aerial due to the reception of horizontally polarized downooming rays from the ionosphere. If desired each vertical long wave aerial may be so loaded that the first full quarter wave is in or near the immediate frequency upon which direction finding is to be carried out. Under such conditions standing waves in the short wave band will be heavily attenuated. At its base each long wave aerial is coupled to the feeder leading to the usual radiogoniometer (not shown) by suitable means such as a transformer T.

In a modification illustrated in the accompanying Fig. 6, instead of constituting each long wave aerial Al by a series of simple short vertical aerial lengths a connected in series by interposed inductances L, the whole vertical aerial consists of a series of inductance coils Ll, L2, each coil Ll being wound in opposite sense to its neighbor L2. As in Fig. 5 the bottom of the aerial may be earthed through any suitable impedance from which the received energy may be taken off, i. e., it may be earthed through the primaryof a transformer T whose secondary leads to the usual radiogoniometer (not shown) employed for the long Wave system. Where such transformer coupling is used the primary and secondary windings are preferably electrostatically shielded from one another as indicated in Figs. 5 and 6 by the vertical line between the transformer windings.

In another modification illustrated in the accompanying Fig. 7 each long wave aerial AI is a simple Vertical aerial and is earthed at its bottom end through a condenser C offering low impedance to the short wave length signals in series with a resistance R. The limb constituted by the condenser C and resistance R in series is shunted by a limb comprising an inductance CH which acts as a choke for the short wave energy in series with an impedance from which received energy may be taken off, i. e., the primary of a suitable transformer T. The impedance provided by the condenser C and the resistance R, in series therewith is so chosen that the vertical aerial, regarded as a line, is correctly terminated so as to avoid reflection of the short wave energy, i. e., as regards short wave energy the aerial is terminated by an impedance equal to the surge impedance. Accordingly short wave energy picked up by each vertical aerial is earthed and re-radiation of such energy is made very small.

The accompanying Fig. 8 illustrates a further modification. In this modification each long wave aerial A! (only one such aerial is shown in Fig. 8) is constituted by a coil consisting of a plurality of, as shown, four solenoid members al, a2, a3, (L4. The members al, a2, which together form one side of the cage, are wound in opposite directions, while the members a3, a4, which form the other cage pair, are also Wound in opposite directions. The members al, a2, are connected together at top and bottom, as are also the members 113, a l, and the connection at the top between the former pair of members is connected through a mast head light EL (to act as an obstruction light to warn aircraft) to the connection at the top between the latter pair of members. At the bottom the two connections are taken through condensers K to the inner conductor of a high freq-uency feeder cable Fl leading to the usual radiogoniometer (not shown) and having its outer conductor earthed as in the usual way. Alternating or direct current lighting energy for the lamp EL is fed in via chokes RFC as shown. Suitable positioning loops CA for the cage aerial thus constituted are provided at suitable points along the height. The arrangement illustrated in Fig. 8 has the advantage that it mitigates against the reception of horizontally polarized electric waves.

The accompanying Fig. 9 shows one convenient way in which the members al, a2, a3, a l, of Fig. 8 may be constructed. In Fig. 9 part of the length of one of these members is shown, as indicated part of the member l. As will be seen, the actual helical conductor al is Wound upon a suitable doped hemp core H. C. and is then served over with suitable doped serving S.

The invention may be summed up in the statement that it enables two different wave length Adcock systems to be positioned one inside the other Without material interference by so arranging matters that the longer wave length aerials cannot set up standing Waves at the shorter wave length and thus cannot receive and reradiate short Wave energy to the detriment of the short wave system.

We claim:

1. A radio direction finding system comprising a plurality of aerials arranged in difierent concentric systems and adapted to operate on different wave lengths, means for determining the electrical characteristics of the aerials of the longer wave system such that they are rendered substantially non-resonant to waves of a shorter wave length appropriate to a shorter wave aerial system, and means for preventing re-radiation of shorter wave energy from said longer Wave aerial system to the detriment of said shorter wave aerial system 2. A direction finding system according to claim 1 in which at least one long Wave vertical aerial system has a plurality of loading coils distributed along the length of the aerial, said coils being spaced apart by and alternating with short aerial lengths, successive loading coils from top to bottom of the aerial being wound in opposite sense.

3. An installation according to claim 1 and in which at least one long wave system consists of a plurality of aerials, each constituted by a cage of helically wound members, oppositely disposed members of the cage being connected in pairs and the members of each pair being wound in opposite sense.

4. An installation according to claim 1 in which at least one long wave system consists of a plurality of aerials, each of which is terminated by an impedance networkwhichsubstantiallymatches the surge impedance and includes a limb grounded at one end and ofiering a low impedance to short wave energy appropriate to a shorter wave system in the installation.

5. In combination, a relatively short Wave antenna system comprising a plurality of symmetrically and vertically disposed energy collecting members, a relatively long wave antenna system comprising a plurality of vertically disposed energy collecting members having an axis of symmetry common to that of said short wave antenna system, means connected to said long wave antenna system for preventing re-radiatio-n of energy of the relatively short waves, said means comprising a plurality of lumped inductances spaced apart and in circuit with different portions of the energy-collecting conductors of said longwave antenna system, whereby the energy collected by either one of said antenna systems may be utilized to obtain directional indications without interfering reactions from the other of said antenna systems.

6. The combination set forth in claim 5 and further characterized in that said lumped inductances are constituted by wire helices wound on a core of rope.

'7. The combination set forth in claim 5 and further characterized in that said lumped inductances as spaced apart along the energy collecting members are alternately right-hand and left-hand helices.

SIDNEY BERTRAM SMITH. ERNEST GREEN.

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