US1465108A - Unidirectional radio receiving system - Google Patents

Description

Aug. 14, 1923. l 1,465,108

E. F. W. ALEXANDERSON UNIDIRECTIONAL RADIO RECEIVING SYSTEM Filed Sept. 16. 1918 2 Sheets-Sheet 1 Fi l. 9 y 2 32K Ann MMM-.W

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Inventor: Ernst F. W. Alexanderson,

lug. 14, 1923. 1,465,108

E. F. w. ALExANDERsoN UNIDIRECTIONAL RADIO RECEIVING SYSTEM 4 Fig. 7. 46 l 42 VWM/44 j fm1 Ei Inventor: Ernst F. W. flexemclerson,

etant ng. 14, i923.

ERNST F. W. .AL

ELECTRIC COMPANY; A CORPORATION OF NEW YORK.

UNIDIRECTIONAL RADIO RECEIVING SYSTEM.

Application tiled September 16, 1918. Serial No. 254,179.

To all whom t may concern.'

Be it known that I, ERNST F. W. ALEX- ANDERsoN, a citizen of the United States, residing at Schenectady, county of Schenectady, State of New York, have invented certain new and useful Improvements in Unidirectional Radio Receiving Systems, of which the following is a specification.

My present invention relates to radio signaling systems and more particularly to a radio receiving system.

One of the objects of my invention is to provide a receiving system which will permit of the reception of signals of any desired wave length at a receivin station to the exclusion of other signals aving the sangre wave length ucoming from directions other than that from which the desired signals come. n l n n Another object of my invention is to prevent interference with the reception of desired signals by an interfering wave of the same wave length which is produced solely for the purpose of interference.

Still another object of my invention is to provide a secret radio signaling system in which it will be impossible for unauthorized persons in some particular locality to receive the signals transmitted from a given station.. .j

Many dierent forms of .receiving apparatus and antenna may be employed in carrying my invention into efect. In the general embodiment of my invention two separate fixed receiving antennae may be employed which are so located with respect to ea other and the direction from which signals are to be received that the signaling currents produced in the two antennae Aby the desired signals will differ in phase. Thiscondition may be secured by locating the centers of distribution of the two antennae at dierent distances from the station from which signals are to be received. Under these circumstances currents produced by waves coming from other directions than that from which the desired signaling wave reaches the antennae except from points located equidistant from the centers of distribution o f the antennae, will also dili'er in phase; The' phase diderence, however, will be different for waves coming from dierent directions. In the case of the desired signals, for example, the current in one antenna will lead thatin the y'second antenna while in the case of signaling waves coming from the opposite direction the current in the second antenna will lead that in the first antenna. By reason of this difference inthe phase relations of the currents produced in the antennae by waves coming from different directions it is possible to neutralize in a receiving circuit the currents produced by the undesired waves without neutralizing the el'ect of the currents produced by the desired signaling Waves. In order to secure the desire neutralization it is not necessar that the two sets of waves should come rom opposite directions. While such a condition is preferable, the necessary phase relations to secure neutralization may exist as lon-g as the two different stations are located in different directions from the receiving station.

rlhe currents produced in the two antenn are impressed upon a receiving circuit. I

introduce between the antennae and the re-` ceiving circuit suitable phase shifting means which are adjusted in such a Way that the currents produced by an undesired wave will neutralize each other in the receiving circuit while the currents produced by the Isignals which it is desired to receive will i act cumulatively in the receiving circuit.

In order to prevent the reception of signals at other points than the receiving station I produce an interfering wave or waves of the same length as the signaling wave-at a point or points so located that the interference in the receiver may be neutralized. If the point or points where it is desired that the signals should not be receivable are all located in substantially the same direction from the transmitting station a single interfering wave set up at some' selected point between the transmitting station and the undesired point-s may 'be suiiicient to produce the desired result. If, however, there are a large number of points at which it is desired to prevent the reception of signals and these points are located in somewhat diiferent directions from the transmitting station it may be desirable to set up two or more interfering waves at points so chosen that the interference may be neutralized at the desired receiving station but so located that all of the interfering waves can not be neutralized at any one of the undesired points.

My invention will best be understood by reference to the following descriptionl taken in connection with the accompanying drawin s in which:

ig. 1 shows diagrammatically one form of receiving circuit which may be employed; Fig. 2 illustrates a convenient form of phase shifter; Fig. 3 is a vector diagram illustrating the phase relations of the different currents in the receivin circuit under one condition of operation; igs. 4 and 5 show two different forms of receiving diagrams which may be obtained by the use of my invention, and Figs. and 7 show modiiied forms of receiving clrcuits.

I have indicated in Fig. l two transmitting stations A and B from which signaling waves of the same length may be transmitted. Between these two stations are located two receiving antennae 1 and 2 extending from the receiving station 3 toward stations A and B respectively. These antennae are preferably made up of long horizontal wires stretched a short distance above the earth or even lying directly on the ground and insulated therefrom. In some cases it may be desirable even to have them buried in the earth. For the most eiiicient operation they should point toward the two stations. This particular form of antennae as well as the location thereof indicated, however, is not essential as will appear from the explanation which follows. The only essential feature is that the centers of distribution of the two antennae, which in the present case are indicated as at the points 4 and 5 should be located at different distances vfrom at least one of stations A and B so that the waves traveling from both of Y these stations will not strike the two receiving antennae simultaneously, and that there will be relatively an appreciable difference 1n time phase of the currents produced by waves traveling in different directions.

The two antenn are grounded at 6 and the coils 7 and 8 which are in series with antennae 1 and 2 respectively form the primaries of the variable intensity coupling transformers 9 and 10 the secondaries 11 and 12 .of which are included in two circuits whlch are provided with phase shifting means. Eachof these circuits should comprise two portions having different phase angle characteristics. In the case illustrated the circuits comprise two branches, one branch which includes resistance 13, capacity 14 and inductance 15 and a second parallel branch which includes resistance 16 and inductance 17. The two branches are preferably so designed that the resultant impedance of the lirst branch is capacitative and the resultant impedanceof the second branch is inductive.

Inductances 15 and 17 form the primaries of variable coupling transformers 18, 19, 20 and 21, thesecondaries 22, 23, 24 and 25 of which are included in a resonant receiving circuit which also' includes an inductance 26 and a tuning condenser 27. Coupling transformers 18 and 19 are preferably ariranged to be varied simultaneously so that when the coupling of one is increased the coupling of thel other is decreased and where the coupling of one is a maximum the coupling of the other is a minimum. The manner in which this may be accomplished is shown in Fig. 2 in which coils 22 and 23 are mounted upon a rotatable axis 28 at right angles to each other within coils 15 and 17 which are in the same plane. A rotation of the aXis'28 by means of the handle 29 changes the position of coils 22 and 23V with respect to coils 15 and 17. When coil 22 is parallel to coil 15 the coupling between the two is maximum. Under theseconditions coil 23 is at right angles to coil 17 and the coupling between the two 1 is substantially zero. If the coils 22 and 23 are then turned the coupling between 15 and 22 will be weakened and the coupling between coils 17 and 23 will be strengthened until coil 22 reaches a position at a right angle to coil 17 If the coils are turned farther in the same direction the action will be reversed and the direction of coupling will also be reversed from that which was present during the first 90 of the movement.

A similar arrangement is provided for cou- 100 pling transformers 2O and 21.

The currents set up in the receiving circuit are impressed in the manner indicated upon the grid circuit of a detector 30 of the pliotron type. In case the Signals to be 105 received are continuous wave signals the receiving pliotron may be made to produce the local oscillations necessary for heterodyne operation by means of a loose coupling between the coil 31 in the plate circuit and. 110

the coil 32 in the grid circuit.

The receiving system which I have de scribed is adapted to receive signals from either station A or station B without interference when waves of the same wave length 115 antennae extend in a direct line between sta- 120 tions A and B and that their centers of distribution 4 and 5 are just a quarter of a wave length apart. An impulse traveling from A will reach antenna 1 a quarter of a period before it reaches antenna 2 and hence 125 the current produced thereby in antenna 1 will lead the current produced in antenna 2 by 90. These two currents may be represented on the diagram of Fig. 3 by the vectors Al and Ag'. An impulse traveling from' 13o VA1 and A2 are in phase.

1 B will, on the other hand, reach antenna 2 'the current in the inductivebranch lags 45 behind the main current, the` vectors of these currents may be indicated by Af, All, Bf, and B1. Assume the same conditions for the circuit connected tov antenna 2 and the currents in the two branches may be represented by vectors A02, AZ, Bc2 and Blz. If

'nowthe coupling transformers are so adjusted that the inductive branch only of` the first circuit is coupled to the receiving circuit and the capacitative branch only of the second circuit is coupled to the receiving circuit the currents impressed upon the receiving circuit will be represented by the vectors Al, Bil, Ag' and BCZ.- It will be seen from the diagram that vectors B1,L and Bc2 are directly opposite in phase and vectors Therefore if B1 and B2 are equal in intensity the will neutralize eachother while A1 and c2 will act cumulatively in the receiving circuit. The two currents Bi1 and B2, may easily be adjusted to the same intensity by varying the coupling of one or both of the intensity coupling transformers 9 and 10.

In case 'it iis desired to receive lsignals from station' B the effect of signals from station A may easily be neutralized by coupling the capacitative branch only of the first antenna circuit to the receiving circuit and coupling the inductive branch only of the second circuit to the receiving circuit.

While in the above explanation the pre ferred` conditions of operation are set forth it is by no means essential to the successful operation of my receiving system that the phase relations of the diiferent currents should correspond with those illustrated in Fig. 3. It is apparent that by suitable design of the phase shifting circuit currents may be produced in the two branches which lead or follow the main current by more than 45 and that by varying thelcoupling between the circuit currents may be impressed upon the receiving circuit which lead or follow the currents produced in the antennae by any desired angle. Hence it will always be possible to so adjust the apparatus that the currents produced by the undesired signals in the two antennae will be neutralized in theV receiving circuit. While under other conditions than-those described it may not bepossible to `make the adjustment so that the two currents produced by the desired signals will be directly in phase, they will always combine with each other at some angle less than 180 and will not neutralize each other when the apparatus is adjusted to neutralize the undesired signals as long as the phase relation between the two currents from station A are not the same as the phase relation between the two currents from station B.

The receiving system which I have described is also adapted for use in a system for preventing the reception of signals by unauthorized persons. In case it is desired to receive signals from station A and prevent the reception of the signals at some other' point an interfering wave of the same length as the signaling wave may be produced at station B.I This wave may be 'neutralized at points between A and B because of the fact that at such points the two waves will be traveling in opposite directions, and hence the phase relation between the two currents from station A will be different from the phase relation between the two currents from station B. At other points, however, in line with stations A and B where the two waves travel in the same direction the interfering wave cannot be neutralized and hence the signals fro station A cannot be received. While it might be possible in case stations A and B are separated by a great distance to receive the signals from A at points nearer station A than station B, by reason of the different intensities of the Wave, at points nearer station B than station A the interfering wave would naturally be much stronger than the signaling wave and hence signals could not be received when the two waves were traveling in the same direction.

In case it is desired to prevent the reception of signals at a single point and this point does not happen to be in line with the transmitting and receiving stations, the interfering wave may be produced at a point between the transmitting station and the point at which it is desired to prevent reception, the only requirement being that this point shall be so chosen that the interfering wave may be neutralized at the receiving station. In case it is desired to prevent 1eception at a large number of points scattered over a single area it may be necessary to produce two or more sets of interfering waves. One manner in which this may be accomplished is indicated in Fig. 4 which represents one form of receiving diagram which may be obtained with a receivingcircuit such as I have described. In this case the receiving apparatus is so adjusted as to neutralize interfering waves produced at the two stations C and D and receive at the same time signals from station A. At any point farther away from' station A than stations C and D it would not be possible to neutralize both interfering waves and at the same time receive signals from station A with the maximum intensity. It might, however, be possible to neutralize the iiiterfering Waves from C and D at some point as E in the line with the receiving and transmitting stations, but in this case the intensity of the signals from A would be represented by the small vector O F on the receiving diagram. To prevent-even the possibility of receivin signals at such a point as E three inter ering waves ma be produced at points such as G, H and as indicated in Fig. 5. All of these waves may be neutralized at the receiving staton by arranging the receiving-circuit so that it will give-a receiving diagram such as that shown in Fig. 5. If the stations are properly located in this manner it would be absolutely impossible to neutralize all of the interfering waves at a point farther removed from the transmitting station A than the interfering stations G, H and I.

In case it is desired to receive signals from a station K, as indicated in Fig. 4, and the elfective direction of the receiving antenna is in the direction of K, C, it will not be possible to neutralize at the same time interfering waves from stations C and D. If, however, the antenna could be so adjusted that its effective direction would be in the direction A, E, it is apparent that the signals from K might be received and at the same time the interfering waves from C and D neutralized. One manner in which this desirable result may be brought about is indicated in Fig. 6. In this case two similar receiving antennae 33 and 34 are provide-d extending in opposite directions from the receiving station and two other similar antennae 35 and 36 extend from the receiving station in directions at right angles to the direction of antennae 33 and 34. The eX- treme ends of antennae 35 and 36 are grounded and the station ends are connected through an impedance which may be of any desired form, but which in the present case I have indicated as a series of condensers 37. By connecting antennae 33 and 34 to different points along the impedance 37 the effective direction of the antenna system maybe varied. For example, if both antennae 33 and 34 were connected to the central point of the impedance37, which is a neutral point with respect to antennae 35 and 36, the effective direction of the system will be along the line of the antennae 33 and 34. If, however, the connections are made at 4some other points as indicated the effective is, if antenna 34 were connected to antenna 36 and antenna 33 were connected to antenna 35, the effective direction of the system would he along a line intersectiig the angle between antennae l34 and 36. aving adjusted the antenna system so that its effective direction is that desired the reception of signals and the neutralization of interference is accomplished in the same manner as with the antenna system shown in Fig. l, the phase shifting means in this case being indicated at 38 and 39 in simplilied for The form of diagram indicated in Fig. 5 could not be obtained with an antenna system such as that shown in Figs. 1 and 6 because of the fact that in this case it is necessary to eliect the complete neutralization of signals from three different directions. In order to accomplish this result a double system such as that indicated in F ig. 7 may be employed. In this case four antennae are used. Two of these 40 and 41 are of the long horizontal type while the other two, 42 and 43, may be of the umbrella type, or any other desired form having their centers of distribution located close to the receiving station. In receiving signals with this system for neutralizing the interference from stations Gr, H. and I the adjustment may be made as follows: The phase shifting devices 44 and 45 may both be adjusted so as to neutralize the interference from G and H. Phase shifting devices 46 and 47 may then be adjusted to neutralize the interference from station I. As a result the effect of waves coming from al1 three directions G, H and I will be eliminated in the receiving circuit 48, and signals be received from A with maximum intensity..

The receiving system which I have described is also of great utility in neutralizing the eiect of strays. When the system is adjusted to neutralize interfering waves coming from any direction the effect of strays coming from that direction will also beneutralized.

I -nd it preferable in carrying out my 1nvention that the receiving antennae should be aperiodic and that the intermediate c1rcuits which contain the phase shiftmg device should also be aperiodic. By arranging the apparatus in this way so that the phase differences are obtained 1n untuned circuits the adjustment of the apparatus is rendered much more nearly independent of frequency variations than would be the case if tuned circuits were employed before the currents are impressed upon the receiving circuit and the neutralization of strays is also rendered much more effective.

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

1. The combination in a radio receiving system of a receiving station, two fixed horizontal receiving antennae extending in opposite directions from said receiving station, said antennae serving as the sole means for collecting energy from the ether, a receiving circuit associated with said antenn and means at the receiving station for shifting the phase of currents impressed from said antennae upon said receiving circuit so that the currents produced by the desired signals will add in said receiving circuit and currents produced by waves of the same wave length as the signaling wave coming from other directions will be neutralized in said receiving circuit.

2. The combination in a radio receiving system of two fixed horizontal receiving antenn extending in opposite directions from a receiving station, each of said antennee having a length of at least the order of magnitude of a quarter of the wave length of the signals which are to be received, said antennae serving as the sole means for collecting energy from the ether, a receiving circuit associated with said antennae and means at the receiving station for shifting the phase of currents impressed from said antennae upon said receiving circuit so that the currents produced by the desired signals will add in said receiving circuit and currents produced by waves of the same wave length as the signaling wave coming from other directions will be neutralized in said receiving circuit.

3. The method of radio signaling which permits a desired reception and prevents an undesired reception of radio signals which consists in producing a signaling wave and in producing an interfering wave of the same wave length as the signaling wave and which travels in a different direction from the signaling wave at points where it is de-. sired to receive the signals and in the same general direction as the signaling wave at points where it is desiredto prevent the reception of the signals and receiving signals at a point where the two waves are travelling in different directions.

4. The method of radio signaling which consists in producing a signaling wave, producing an interfering wave of the same wave length as thexsignaling wave and which travels in a different direction from that of the signaling wave at certain points where it is desired to receive the signals and inthe same general direction as the signaling wave at other points and receiving signals atl points where the two waves are traveling in diierent directions by neutralizing the effect in the receiving apparatus of the interferingl wave.' l

- 5. The method of radio signaling which` consists in transmitting signals by means of a signaling wave, producing a plurality of interfering waves of the same wave lengt as the signaling wave and which travel inl different directions from that of the signaling wave at certain points where it isdesired to receive the signals and in the same general direction as the signaling wave at other points and receiving the signals at a point where the interfering waves travel in a dii'erent direction from that of the signaling wave by neutralizing the effects of the interfering waves in the receiving apparatus.

6. The combination in a radio receiving system of an aperiodic receiving antenna, a receiving circuit'associated therewith and means for varying the phase of the current impressed upon the receiving circuit from the receiving antenna, said phase varying means comprising an aperiodic intermediate circuit having two portions with different phase angle characteristics, means for cou-d p ling both of said portions to the receiving circuit, and means for simultaneously varying .the coupling of both portions to the receiving circuit.

7. The combination in a radio receiving system of an aperiodic receiving antenna, a receiving circuit associated therewith and ineans for varying the phase of the current impressed upon the receiving circuit from the receiving antenna, said phase varying means comprising an aperiodic intermediate circuit having two arallel branches having different phase ang e characteristics, means for coupling both of said branches to the receiving circuit, and means for simultaneously varying the coupling of both branches to t e receiving circuit.

8. The combination in a radio receiving system of an aperiodic receiving antenna, a receiving circuit associated therewith and means for varying the phase of the -current impressed upon the receiving circuit from the receiving antenna, said phase varying means comprising an aperiodic intermediate circuit having two parallel branches having different phase angle characteristics, means for coupling both of said branches to the receiving circuit, and means for simultane-l ously varying the coupling of both branches to the receiving circuit, said coupling means being so arranged that when the coupling of one branch is at a maximum the coupling of the other branch is a minimum.

9. The combination in a radio receiving system of an aperiodic receiving antenna, a resonant receiving circuit associated therewith, and means for varying the phase of the current impressed upon the receiving circuit from the receiving antenna, said phase varying means com rising an aperiodic, intermediate circuit aving twoportions of dii'erent phase angle characteristics, means for coupling both of said portions to the receiving circuit, and means for simultaneously varying the .coupling of both portions to the receiving circuit, said 'coupling means being so arranged that as the coupling of'one portion is increased the coupling of the other portion is decreased.

10. The combination in a radio receiving system of two fixed aperiodic receiving antennae, a resonant receiving circuit associated with said antennae, and means forv varying the phase of the current impressed upon the receiving circuit from the two antennae comprising an aperiodic intermediate circuit between each antennae and the receiving circuit, each of said intermediate circuits comprising two portions having different phase angle characteristics, means for coupling both of said portions of each intermediate circuit to the receiving circuit, and means for simultaneously varying the coupling of both portions of each intermediate circuit to the receiving circuit.

11. The combination in a radio receiving circuit of two fixed aperiodic receiving antennae, a resonant receiving circuit associated with said antennae, and means for varying the phase of the current impressed upon the receiving circuit from the two antennae comprising an aperiodic intermediate circuit between each antenna and the receiving circuit, each of said intermediate circuits comprS'ing two parallel branches having different phase angle characteristics, means for coupling both of said branches of each intermediate circuit to the receiving circuit, and means for simultaneously varying the coupling of both branches .of each intermediate circuit to the receiving circuit.

12. The combination in a radio receiving system of two fixed aperiodic receiving antennae extending in opposite directions from a receivingu station, a receiving circuit associated with said antennae and means for varying the phase of the current impressed upon the receiving circuit from the two antennae comprising an aperiodic intermediate circuit between each antenna and the receiving circuit, each of said intermediate circuits comprising two parallel branches one of which has a resultant capacitative impedance and the other a resultant inductive impedance, means for coupling both of said branches of each intermediate circuit to the receiving circuit, and means for simultaneously varying the coupling of both branches of each intermediate circuit to the receiving circuit, said coupling means being so arranged that as the coupling of one branch is increased the coupling of the other branch is decreased.

13. The combination in a radio receiving system of a receiving antenna, a receiving circuit associated therewith and means for varying the phase of the current impressed upon the receiving circuit from the receiving antenna, said phase varying means comprising an intermediate circuit having two parallel branches one of which has a resultant capacitative impedance and the other ing antenna, said phase varying means comi prising an intermediate circuit having two parallel branches one of which. has a resultant capacitative impedance and the other a resultant inductive impedance, means for coupling both of said branches to the receiving circuit, and means for simultaneously varying the coupling of both branches to the receiving circuit, said coupling means being so arranged that ywhen the coupling of one branch is a maximum the coupling of the other branch is a minimum. y

15. The combination in a radio receiving system of a receiving antenna, a receiving circuit associated therewith and means for varying the phase of the current impressed upon the receiving circuit from the receiving antenna, said phase varying means comprisingan intermediate circuit having two parallel branches one of which has a resultant capacitative impedance and the other a resultant inductive impedance, means for coupling both'of said branches to the receiving circuit, and means for simultaneously varying the coupling of both branches to the receiving circuit, said coupling means being so arranged that as the coupling of one branch is increased the coupling of the other branch is decreased.

16. The combination in a radio receiving system of two fixed receiving antennae eX- tending in opposite directions from a receiving station, a receiving circuit associated with said antennae and means for varying the phase of the currents impressed upon the receiving circuit from the two antennae comprising an intermediate circuit between each antenna and the receiving circuit, each of said intermediate circuits comprising two parallel branches one of which has a resultant capacitative impedance and the other a resultant inductive impedance, means for coupling both of said branches of each in' termediate circuit to the receiving circuit, and means for simultaneously varying the coupling of both branches of each intermediate circuit to the receiving circuit.

17. The combination in a radio receiving system of a receiving station, two fixed horizontal receivingantennae extending in different directions from said receiving station, said antennae serving as the sole means for collecting energy from the ether, a' receiving circuit associated with said antennae and means at the receiving station for shifting the phase of currents impressed 4from said antennae upon said receiving circuit so that the currents produced by the desired signals will add in said receiving circuit' antennae having their centers of distribution separated by a distance of at least the order of magnitude of a quarter wave length of the signals to be received, at least one of said antennae being of the horizontal type extending away from the receiving station and serving as the sole means for collecting energy from the ether and conveying it to the receiving station from the direction in which it extends,.,a receiving circuit associated with said antennae and means at the receiving station for shifting thephase of currents impressed from said antennae upon said receiving circuit so that the currents produced by the desired signals will add in said receiving circuit and currents produced by waves of the same, wave length as thesignaling waves coming from other directions will be neutralized in said receiving circuit.

19. The combination in a radio receiving system of a receiving circuit, two receiving antennae, one of which has its center of distribution located near the receiving station and the other of which is of the horizontal type extending away from the receiving station and having its center of distribution located at a point separated from the receiving station by a distance of at least the order of magnitude of a quarter wave length of the signals to be received, a receiving circuit associated with said antennae and means for shifting the phase of currents impressed from said antennae upon said receiving circuit so that the currents produced by the desired signals will add in said receiving'circuit and currents produced by waves of the same wave length as the signaling wave coming from other directions will be neutralized in said receiving circuit.

20. The combination in a radio receiving system of two fixed receiving antennae, a resonant receiving circuit associated with said antennae, means for simultaneously impressing upon said receiving circuit from each of said antennae currents derived from the same signal wave but differing in phase, comprising two portions of the receiving system having different phase angle characteristics, means for coupling both of said portions to the receiving circuit and means for simultaneously varying the coupling of both portions to the receiving circuit.

21. The combination in a radio receiving system of a receiving station, a plurality of receiving antennae at least two of which have their centers of distribution separated by a distance of at least the order of magnitude of a quarter wave length of the signals to he received, a receiving circuit associated with said antennae, means associated with one pair of said antennae for neutralizing in the receiving circuit the effect of signaling waves coming from a certain predetermined direction, and means associated with another pair of said antennae for neutralizing at the same time in the receiving circuit the effect of signaling waves coming from another direction.

22. The method of adjusting a radio receiving system comprising a plurality of fixed receiving antennae to receive radio signals of a given wave length coming from a desired direction to the exclusion of signals of the same wave length coming from other directions which consists 'in first neutralizing the effect in a receiving circuit of signals coming from one of the l'other directions by adjusting the coupling between one pair of antennae and the receiving circuit and then neutralizing the effect in the receiving circuit of signals coming from another of the undersired directions by adjusting the coupling between another pair of antennae and the receiving circuit.

23. Phase varying means comprising a pair of coupling transformers each of which consists of a fixed coil and a. coil movably mounted for rotation with respect to the fixed coil, the movable coils of the two transformers being arranged so that they may be rotated. simultaneously with respect to the fixed coils and that when the couplin of one transformer is a maximum the couing of the other is a minimum.

24. Phase varying means comprising a pair of coupling devices adapted to impress two currents of different phase angle charl acteristics upon an electric circuit and means for simultaneously varying the coupling of the two devices. f

25. Phase varying means comprising a Ipair of coupling devices adaptedto impress two currents of different phase angle characteristics upon an electric circuit and means for simultaneously varying the coupling of the two devices in such a way that when the coupling of one device is a maximum the coupling of the other device is a minimum.

In witness whereof, I have hereunto set my hand this 13th day of September, 1918.

ERNST F. ALEXANDERSON.

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