US2320521A - Radio beacon system - Google Patents

Description

June 1, 1943. KEAR 2,320,521

RADIO BEACON SYSTEM Filed Feb. 27, 1935 2 Sheets-Sheet 1 F17. .2 F27. E E 7.3

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AMPLIFIER g E Qwue/wbom [E5 FRANK G. KEAR v '9 AMPLIFIER 3 E $53 June 1., 1943.

F. G. KEAR RADIOBEACON SYSTEM Filed Feb. '27-, 1935 2 Sheets-Sheet 2 FRANK G. KEAR Patentecl June 1, 1943 RADIO BEACON SYSTEIE Frank G. Kear, Washington, D. C., assigncr to Washington Institute of Technology,

Inc.,

Washington, D. (3., a corporation of Delaware Application February 2'7, 1935, Serial No. 8,541

20 Claims.

This invention relates to radio beacon systems and, more particularly, to the establishing of a two-course or four-course beacon system by the use of non-directional radiators.

It has heretofore been proposed to substitute for the crossed loop transmitting means, as originally employed in radio beacon transmission, a system employing four vertical antennas, such change being proposed in order to do away with the errors introduced into the radio beacon operation by the inherent nature of the crossed loop system. It has been found, however, that the systems employing four vertical antennas are not entirely free from certain disadvantages inherent in the crossed loop systems. In the use of a beacon system employing either the crossed loop or four-vertical antenna types of array, the characteristic signal is reversed on opposite sides of the beacon transmitter. Thus, in a visual system, it is necessary to turn the reed box over as the transmitter is passed, in order to maintain the previous relation of the characteristic signals. In an aural system the pilot, when passing the beacon transmitter, must constantly remember the reversed arrangement of signals in order to correctly orient the aircraft with respect to the transmitter. It may also be noted that the use of the four vertical antennas has materially increased the installation cost of the system. Further, in the use of a system employing four vertical antennas as a transmitting array, it is necessary to maintain the tuning of the vertical antennas and the phasing of the currents in them in order to maintain the stability of the courses, it being necessary in such systems to correctly tune and phase four circuits.

It is therefore an object of the present invention to provide transmitting means for providing a two-course or four-course beacon, which means will not be subject to the errors and disadvantages of prior systems.

A primary object of the invention is to provide a transmitting system for providing either a twocourse or four-course beacon, which system will employ, in either case, only two non-directional radiators.

Another object of the invention is to provide a transmitting system for providing either a twocourse or four-course beacon, which system will not be subject to errors resulting from reflection from the Kennelly-Heaviside layer.

Another object is to provide a transmitting system for a two-course beacon in which system the same characteristic signal will always be found on the same side of the beacon course, thereby further aiding in simplifying the navigation of aircraft.

A further object is to provide a transmitting antenna array which will require less tuning and phase adjustment than prior systems in order to maintain course stability.

A further object is to provide circuit arrangements and means for energizing two non-directional radiators to provide either a two-course or four-course beacon.

Other objects and novel features of the invention will be made apparent to those skilled in the art by the following description and the annexed drawings which, it will be understood, are merely illustrative of the invention and impose no limitation thereon not imposed by the appended claims.

Referring to the drawings, in which similar reference numerals refer to like parts,

Fig. 1 illustrates the field pattern resulting from the energization of the antennas of a two-antenna system in one manner,

Fig. 2 illustrates the field pattern resulting from the energization of the antennas of a two-antenna system in a second manner,

Fig, 3 illustrates the combined field pattern resulting from the. combination of the field patterns of Figs. 1 and 2, according to the present invention,

Fig. 4 is a schematic drawing of an antenna arrangement for producing the field patterns of Figs. 1, 2 and. 3,

Fig. 5 discloses a circuit arrangement for the antennas in accordance with the schematic showing of Fig. 4,

Fig. 6 discloses a circuit arrangement for energizing the circuit of Fig. 5,

Fig. 7 discloses a second circuit for energizing the circuit of Fig. 5,

Fig. 8 illustrates the field pattern resulting from the energization of two non-directional radiators in a system for the production of a four-course beacon,

Fig. 9 illustrates the field pattern resulting from the energization, in a different manner, of two non-directional radiators, for the production of a four-course beacon,

Fig. 10 illustrates the combination of the field patterns of Figs. 8 and 9,

Fig. 11 is a schematic view showing the arrangement of two non-directional radiators for transmission of a four-course beacon,

Fig. 12 is a schematic showing of a system for energizing the antennas of Fig. 11,

Fig. 13 is a circuit diagram illustrating a secnd circuit arrangement for transmitting a twocourse beacon from two non-directional radiators, and

Fig. 14 is a circuit diagram illustrating a second circuit arrangement for transmitting a fourcourse beacon from two non-directional radiators.

It has been determined that if two non-directional radiators be so spaced and the currents in the antennas so phased that the algebraic sum of the space and time phase angles is 180, a space pattern of cardioid form will be produced, the maximum of which will extend alon a line joining the two antennas and in the direction of the lagging antenna. This effect is illustrated in Fig. 1, it being noted that in this example the antennas are spaced one-quarter wave length or 90 and the energization of antenna Vv' leads that of antenna E by 90. If a current be supplied to the antennas so that the energization of antenna W lags that of antenna E by 90, a cardioid extending in the opposite direction will be produced. This effect is illustratedin Fig. 2 and it will be noted that in this case the maximum of the cardioid pattern is on the line joining the two antennas and in the direction of antenna W. If, now, the antennas be energized either alternately or simultaneously two-coursebeacon are separated 90 in space and are energized by currents displaced 90 in time phase. It is tobe understood that these values are only a special case of the invention and are employed only for the purpose of simplifying the discussion. It is contemplated by the invention that the two non-directional radiators be spaced K degrees apart and energized by currents displaced R degrees in time phase, when K+Rl80.

In Fig. 4 there is schematically illustrated a radiating array according to the present invention which is so arranged as to establish radiation fields providing two courses in space.

This arrangement comprises the antennas E, W which will be assumed to be spaced a quarter Wavelength apart. These antennas may be supplied with modulated radio frequency energy through transmission lines 3, 4 and, according to the present invention, are connected by a transmis sion line I which in this example has an electrical length of 90. It will be apparent that voltage supplied to radiator E will produce a similar voltage in radiator W with a 90 time lag, while a voltage supplied to radiator W will produce a similar voltage in radiator ,E with a 90 time lag.

A circuit arrangement for the antenna system illustrated in Fig. 4 is disclosed in Fig. 5 and it will be seen that in this circuit arrangement radio frequency voltages modulated by differing characteristic signals are applied at C, D from a radio frequency source (not shown) to the transmission lines 3, 4 through coupling transformers 5, 6. Eachof the transmission lines 3, 4

includes the primary I of a transformer, each of said transformers having two secondaries 8, 9. The secondary 8 of each transformer is connected in a circuit l9 comprising a transmission line having an electrical length of 90, While the secondaries 9 are respectively connected to nondirectional radiators E, W which are grounded at it and M, respectively. It will be noted that the antennas E, W are spaced a quarter wavelength apart in accordance with the schematic showing of Fig. 4, although as stated above, the invention contemplates that the antennas be spaced K degrees apart and energized by currents displaced R degrees in time phase, when K+R l80.

It will be seen that if a voltage is supplied to antenna E through the transmission line 3, primary 1 and secondary 9, a similar voltage will be supplied to the transmission line I9 through primary l and secondary 8 and a similar voltage with a 90 time lag will, therefore, be produced in antenna 'W. A cardioid field pattern will be produced by such energization and such pattern will have its maximum in a line joining the antennas E, W and extending in the direction of antennaW. Similarly, energy supplied directly to antenna W through transmission line 4, primary l and secondary 9 'will be transmitted to antenna E through transmission line! and will appear there with a lag equal to the length of line H]. A second cardioid-shaped field will be produced by the radiation'of this energy, the maximum of such field being in the line E, W and in the direction of antenna E. If equal power is supplied to antennas E or W either simultaneously or alternately, reverse-phase cardioids will be produced in the manner described and their intersection will lie on a line erpendicularly bisecting a line joining the two antennas, such line of intersection providing a course extending in two directions from the antenna station.

The radio frequency energy supplied to the two antennas may be modulated with any desired signals in order to define the course. The usual A and N signals for aural beacons or the 87 and 65 cycle signals for visual beacons may be employed. In the operation of a system employing characteristic signals of this type, one of the two cardioids will be produced from the radio frequency energy modulated by the A or 87 cycle signal, while the other cardioid will be produced from the radio frequency energy modulated by the N or 65 cycle signal. It will, therefore, be seen that each of the two cardioids will be impressed with only one of thetwo characteristic signals. Each signal 'will'therefore always be greater than the otheron one side of the course defined by theline of intersection of the radiating fields of the antennas and an aircraft flying along such course will not encounter any reversal of indication.

As stated above, the desired space patterns may be produced alternately if a so-called aural beacon is to. be provided at a receiver located in the radiated fields, or continuously if a so'-c'alled visual beacon is desired. A circuit for supplying voltages alternately to the circuitsC, D of Fig. 5 is disclosed in Fig. 6. In this circuit a master oscillator l5 supplies voltages at radio frequency to a beacon amplifier l5, the output of which is connected to a link circuit l'l containing a keying relay it which may be operated to alternatelyenergize th circuits 0 and D to supply power to lines 3 and 4. When line 3 is'excited the array will produce a cardioid whose carrier at the keying relay l8.

If a visual system is being employed, the circuit for energizing the antennas of Fig. may

be as disclosed in Fig. 7. In this circuit a master oscillator l9 supplies voltages at radio frequency to the two amplifier branches 20, 2|, these branches being coupled respectively to the circuits 0 and D for supplying the lines 3 and 4. Any desired coding, such as the 87 and 65 cycle audio frequency modulations, may be impressed on the carriers and supplied continuously to the antennas E and W. It will therefore be seen that the array will constantly produce two cardioids, one having its maximum in the direction of one antenna and being modulated with the 87 cycle frequency, and the other having its maximum in the direction of the other antenna and being modulated with th 65 cycle frequency. The line of intersection of the two cardioids will perpendicularly bisect the line joining the two antennas and it will be seen that th 8'1 cycle frequency and the 65 cycle frequency will each always be of greatest intensity on one side of the course on both sides of the line joining the antennas. Consequently, it will not be necessary for the pilot of an aircraft flying on the course to turn over the reed box or, if a reed converter is used, switch over the converter when crossing over the beacon station. The course may be bent as desired by varying the relative amplitudes of the voltages supplied to the lines. The beacon sidebands, being of different frequency, will not combine in space but will produce a pair of cardioid patterns, as described, with a course in the same line as in the case of the aural beacon. The carriers will combine in space but the resultant carrier from each antenna is in time phase with the other and the pattern is an ellipse of slight eccentricity which will not disturb th courses.

The invention also provides other means for providing a two-course beacon by the radiation of energy from two non-directional radiators in such a manner as to establish two intersecting radiated fields each of which will have a cardioid transmission characteristic and which will be reversed in phase. By this means according to the invention, there is provided a circuit for supplying to two non-directional radiators voltages -which would cause the establishment of a radiated field having a circle pattern, a circuit for supplying to the non-directional radiators currents which would cause the establishment of a radiated field having a figure-of-eight pattern, and a circuit for combining these currents and supplying such combined currents to the nondirectional radiators. The combined currents will caus the radiation from the antennas of energy so phased as to produce two reversed phase radiation fields each of which will have a cardioid transmission characteristic. The intersections of these radiated fields will define two courses in space extending on opposite sides of the line joining the two antennas. Such means are disclosed in Fig. 13 of the drawings.

The system disclosed in Fig. 13 comprises a bridg circuit L having the arms 40, 4|, 42 and 43, which arms are connected at terminals 44, 45, 46 and 41. Fixed condensers 48 and 49 are inserted in arms 40 and 4|. Two non-directional radiators E and W are provided and are coupled to ground through inductance coils 50, 5| which form the secondaries of input transformers, the primaries 52 and 53 of which are included in the circuit of a transmission line 54 having an electrical length of in the present case. The antennas E and W are spaced, in the case under discussion, a quarter wave-length apart. The transmission line 54 also includes a coil 55, the same being in inductive relation to-a primary coil 56, the purpose of which arrangement will appear more fully hereinafter. Voltages at radio frequencies and modulated to provide any characteristic signals desired are supplied through input circuits C, D to input transformer 51, 58. One terminal of the secondary of input transformer 51 is connected by lead 59 to terminal 45 of the bridge L, while the other terminal of the said output transformer is connected to terminal 41 of the bridge through lead 60. The output terminals of the transformer 58 are connected to bridge terminals 44 and 46 through leads BI and 62 respectively. Th circuit across terminals 45, 46 of the bridge is completed by leads 65, 66 which are connected at their one ends to the terminals 45, 46 and at their other ends to the terminals of primary coil 56. The circuit across terminals 46 and 41 of the bridge is completed by leads 61, 68, one of which, lead 51, is connected at its one end to bridge terminal 45 and at its other end to the midpoint 69 of transmission line 54, which point is also connected to ground at 10. The other lead 68 is connected at its one end to bridge terminal 41 and at its other end to the secondary coil 55 in the transmission line 54 by a center-tap 1|.

Assuming that voltages at radio frequency and modulated by any desired characteristic signals are being supplied to input circuits C and D, current will flow from the secondary of transformer 51 through lead 59 to bridge terminal 45 where it divides, part flowing through arms 4| and 40 of the bridge and lead (ill to the other terminal of transformer 51. The rest of thecurrent flows through bridge arm 42, lead 56, winding 56, lead 65, bridge arm 42, bridge arm 43, lead 61, terminal 69, transmission line 54, windings 52 and 53, winding 55, center-tap 1| of winding 55, lead 68, bridge arm 43 and lead 60 to the secondary of transformer 51, thereby completing the circuit. It will be seen, first, that the completion of this circuit energizes winding 56 causing a current to flow therein. Current in winding 56 will induce a current in winding 55, whch, being series connected to the windings 52, 53 will cause currents to flow in opposite directions in these coils. The voltages across coils 52, 53 will thus be displaced in phase. Such excitation of windings 52, 53 will induce voltages having a phase displacement of 180 across antenna coils 50, 5| and a radiated field having a figure-ofeight form will be produced.

The above-described circuit being completed between terminal 69 and center-tap 1|, in-phase voltages will be impressed across windings 52, 53, these windings being connected in parallel with the terminal 69 and center-tap 1|. Such excitation of windings 52 and 53 will cause in-phase currents to be induced in the antenna coils 50, 5| and a radiated field having substantially a circle form will be produced.

The in-phase and reversed-phase voltages across antenna coils 50, 5| will not-causeseparate fields to be produced, but the combined currents in the antenna coils willproduce a radiated field of cardioid shape, resulting -from the combination of the circle and figure-of-eight field. In the case under discussion, the leads 65,

66 compose a transmission line or time delay circuit whose total delay is of the order of an odd multiple of ninety degrees, plus or minus.

Current from circuit D will flow through lead 62 to bridge terminal 46 where it divides, establishing two circuits. One of these is completed through bridge arm 42, lead 65, coil '56, lead 66, bridge arms 42 and..4l and lead 6! to the second terminal'of the input circuit. The other circuit is completed through bridge arm 43, lead 61, terminal 69, transmission line 54, windings 52 and 53, winding 55, center-tap H, lead 68, bridge arms 43 and 40 and lead 6| to the second terminal of the input circuit D. It is evident, from the principles of Wheatstone bridge circuits, that the result of this flow of current is to produce across the arm 42 the sum of the two voltages at a given instant, and across, arm 43'the difference of these voltages, or vice-versa. This effect is independent of the phase relation of the ,volt- 5 ages applied at C and D, although for convenience this is customarily 90. It is understood that should carrier suppressed transmission be employed this phase angle has reference to the angles between the axes of projection of the side.- band frequencies considered as rotating. vectors. The voltages across windings 52 and .5.3j'.will be 180 displaced in phase due to theseries connectionof the elements and. reversed-phase voltages will thereforeibe induced in lantenna coils 50, 5| thereby producing a radiated .field: of figure-of-eight form.

The terminal 69. and center-tap .H being connected in parallel across windings 52, 53, voltagesapplied across these two points will cause in-phase currents to fiow in windings, '52, 53 which will induce in-phase currents in antenna coils 50, 5|. A radiated field havingcircle form will therefore be produced. As discussed above, the circle and figure-of-eight .fields will combine in space to produce a cardioid field whosemaximum will lieon a linejoining thetwo antennas and extending ina direction opposite. to thatof the cardioid, field produced by currents from,input circuit C. This action is caused by theoperation of the bridge circuit as previously described.

It will therefore be seen that two radiatedfields of cardioid shapeand having. their maximums extending in opposite directions .willbe produced. These fields may be produced alternately in the case of an aural system'by alternate energization of input. circuits C and D, or may be simultaneously produced by continuous .energization oflthe .two. circuits, if .a visualsystem isdesired. In:.either case the carriers supplied to thetwo course for aerial navigation.

The-present-invention also contemplates the provisionoi means .for producing a-four-course beacon froina system employing onlyv two nondirectional radiators. As stated hereinbefore. it has heretofore been proposed to provide a fourcourse beacon by energizingfour verticalan tennas in pairs to produce two intersecting fig,- ure-of-eight patterns, the points ofintersection of which determine four courses inspace. 7 Such systems have been substituted for the prior crossed p systems in order to eliminate the effects due to reflection from the Kennelly- Heavisidelayer, known as night efiects. By reason of the present invention it is possible to produce a four-course beacon by the use of only two non-directional radiators, thereby materially reducing the installation costs of the transmitting system, and eliminating errors due to night effeet.-

It may be desirable to establish a four-course beacono-f either the aural or visual type and while the following discussionspecificallyrelates to a visual system, it will be applicable to an aural system as well. The visual system employs usually the 87 cycle and-65 cycle modulations of the carrier to provide characteristic signals. According to the present invention two non-directional radiators E-and W, as disclosed in Fig. 8, are provided and are spaced a half wave-length apart. These antennas are supplied with voltages at radio frequency modulated by the 87 cycle frequency. If the 87 cycle antenna currents are in time phase a figure-of-eight field as illustrated in Fig. 8 results. The same antennas aresupplied with voltages at radio frequency modulated by the 65 cycle frequency. If the-65 cycle antenna currents are separated in time phase,.-the figure-of-eight field of Fig. 9 results. If the two antennasbe excited simultaneously oralternately in this manner, the two figure-of-eight fields combine as illustrated in Fig. 10, the overlapping portions thereof providing four equi-signal courses OP, 0Q, OR and OS. The angular relation of the four courses may be varied by varying relatively the amplitudes of the supplied V0ltages.

A schematic showing of an antenna. array for the production of thefieldsdescribed is illustrated in Fig. 11. The antennas E, W are. spaced a half wave-length apart and are separately excited through transmission lines X and Y. Anexciting circuit for the antennas E and W is illustrated in Fig. 12 and it will be seen that this circuit provides for the supplying of both the 65 cycleand 87 cycle frequencies to both ofthe antennas. A source of radio frequency (not shown) may supply voltages atradio frequency to modulating circuits for impressing the signal frequencies. The output of the modulating circuit 30 is supplied through leads 32 to the line X which supplies antenna E, and through leads 33 to the line Y which supplies antenna W, these voltages being in phase. The output of modulating circuit 3! is suppliedto line X through leads 34 and in out-of-phase relation to line Ythrough leads 35. Voltages having an identifying characteristic, such as the 65 cycle modulation for example, are supplied to the two antennas in in-timephase from the modulating circuit 30 and produces a figure-of-eight field of the type illustrated in Fig; 8, due. to the phasing of the currents and the spacing of the antennas. The 87 cycle currents supplied to one of the antennas from the modulating circuit 3| are 180 out of time phase with the currents of the same frequency supplied to the other of the antennas, thereby producing a figure-of-eight field of the type illustrated in Fig. 9. Simultaneous energization of the two antennas by the 87 cycle and 65 cycle frequencies, in the manner described, will produce a combined field resulting from the combination of the in-phase and out-of-phase frequencies, which field will be of the double figureof-eight type as illustrated in Fig. 10. The two figure-of-eight fields overlap in space and the points of intersection of the fields determine four courses for aerial navigation.

It will be apparent that if an aural system is desired the lines may be energized by alternate in-phase and out-of-phase voltages modulated by the usual A and N or other desired signals. The spacing of the antennas, and the phasing of the exciting currents will remain the same and the field produced will also be the same, except that at any given instant only one of the fields of Figs. 8 and 9 will exist.

A second means according to the invention for producing a four-course beacon from a circuit employing two non-directional radiators is disclosed in Fig. 14. In this circuit there is provided an antenna array consisting of the two nondirectional radiators E and W which are spaced half a wave-length apart and are connected by transmission lines SI, 89 at the junction of which are connected two coils 82, 84 of a three-winding transformer, the terminals of coil 84 being conmodulated by any desired characteristic signal.

A second source of radio frequency current modulated by any desired characteristic signal is connected by leads 9|, 92 to coils 82 and 84 through center-taps.

If radio frequency currents modulated by any desired characteristic signal, such as the usual A or N signal for an aural system or the 87 cycle and 65 cycle signals for a visual system, are sup plied to coils 82 and 84 through leads 9|, 92 which are connected to the centers of such coils, inphase voltages will be supplied to antennas E and W and a radiated field of figure-of-eight form having its major axis at an angle of 90 to the line joining the antennas will be produced. If carrier frequency currents modulated by any desired characteristic signal are now supplied to coil 83 through leads 85, 86, similar voltages will be induced in coil 82 and 84 and out-of-phase voltages will be supplied to antennas E and W, whereby a radiated field of figure-of-eight form will be produced, and such field will have its major axis on the line joining the antennas. The two fields so produced will combine in space to produce a field of the type shown in Fig. 10 and the intersections of the fields will provide four courses in space for aerial navigation.

The foregoing description and the annexed drawings disclose certain forms of the invention, but it will be apparent to those skilled in the art that modifications and improvements of the invention may be made without departing in any way from the spirit or scope of the invention, for the limits of which reference must be had to the appended claims.

I claim:

1. A radio beacon system comprising two spaced non-directional antennas, means connect ing said antennas and having a known electrical length, two sources of difierently modulated radio frequency current for exciting said antennas, and means for dividing the current from each source to supply to said antennas from each source in-phase and out-of-phase currents.

2. A radio beacon system comprising two spaced non-directional antennas, a transmission line connecting said antennas, means for inducing series currents in said transmission line to produce out-of-phase currents in said antennas, and means for inducing parallel currents in said transmission line for producing in-phase currents in said antennas, whereby a radiated space pattern resulting from the combination of said in-phase and out-of-phase antenna currents is produced.

3. In the production of a radio beacon through the agency of a pair of spaced radiators connected to the opposite sides of a phase-shifting network, the steps of amplitude modulating a carrier with two different audio frequency signals to thereby produce two separate waves each resulting from a difierent one of such modulations; continuously supplying one of said waves to one of said sides of said network and continuously supplying the other of said waves to the other of said sides of said network; and radiating the resultant waves from said radiators.

4. In a radio beacon, the combination which comprises: a phase-shifting network having first and second sides; means for continuously supplying a wave resulting from amplitude modulation of a carrier of given frequency with one modulation frequency to the first side of said network; means for continuously supplying a wave resulting from amplitude modulation of a carrier of the same given frequency with another modulation frequency to the second side of said network; and a pair of spaced radiators respectively connected to the first and second sides of said network.

5, A radio beacon system comprising two spaced non-directional antennas, an exciting circuit inductively coupled to one of said antennas for energizing said antennas with one of a pair of signals, a second exciting circuit inductively coupled to the other of said antennas for energizing said antennas with the other of said pair of signals, and a transmission line having a predetermined electrical length inductively coupled to both said exciting circuits.

6. In a radio beacon, the combination of a source of radio frequency, means for modulating a portion of the radio frequency produced by said source at an audio frequency, phasing means and antenna radiating means for radiating in a definite direction said modulated radio frequency with a space pattern cardiodal in shape, additional means for modulating a portion of said radio frequency at a second audio frequency different from said first audio frequency, a second phasing means associated with said second modulated radio frequency and producing a second space pattern in space cardioidal in shape from said radiating means and in a direction opposite to said first pattern, said first and said second cardioidal space patterns intersecting in space to form two zones where said first modulated radio frequency is equal in intensity to said second modulated radio-frequency.

'7. A radio beacon system for establishing a plurality of zones of equal signal intensity comprising two spaced non-directional antennas, means for producing in said antennas voltages causing a radiation having a cardioid field pattern whose major'axis is inthe direction of one of the antennas, andmeans for simultaneously producing in said antennas voltages causing a radiation having a cardioid field pattern whose majoraxis is in the direction of the other of said antennas, and meansfor differently modulating the energy in said antennas in order to produce differently modulated cardioid radiation fields:

8. A radiobeacon system' for establishing a plurality of zones'of equal signal intensity comprising two spaced non-directional antennas, means for periodically producing in said antennas voltages causing a radiation having a cardioid-fieldpattern whose major axis is in the direction of one of the antennas, and means operating alternately with said first means for producing in said antennasvoltages causing a radiationhaving a cardioidfield pattern whose major axis is in thedirectionof theother ofsaid antennas, and means for differently modulating the energyin'said antennas in order to produce difierently modulated cardioid radia- 0 tion fields.

9. 'A radio beacon system'comprising two nondirectional antennas spaced K degrees apart, a transmission line having an electrical length of R degrees connecting said antennas, two sources of-modu1ated-radio frequency energy supplying said antennas; a bridge circuit connected to said sourcesand to said transmissionline for di viding the currents from saidsources and supplying aplurality of--in-phase and a plurality of out-of-phase currents to= said transmission line whereby two intersecting field patterns are radiated fromsaid antennas, and K+R-= 180.

10, A radio beacon'systenr for producingtwo intersecting cardioid-shaped radiated fields, comprising two non-directional radiators spaced K 'apart, means for-supplying directly to one of saidradlators radio frequency energy characterized by one-of .two different signals, means for supplying directly to the other of said radiators radio frequency energy characterized by the second of said signals, and means having an electrical 1 length of R connecting said radiators whereby modulated energy directly supplied to each radiator will appear in the other with a phase displacement of R, the sumof K and R being approximately 180;

11. A radio beacon system according to'claim' 10, in which a transmission line having an electricallength of- R connects thetwo radiators.

121A method of producing a-radio beacon with a pairof spaced radiators connected to the opposite sides of a phase-shiftingnetwork, which includes the steps of continuously supplying to one of said sides of said phase-shifting network a wave resulting from amplitude modulation of a carrier of given frequency with a modulation frequency, continuously supplying to the other of said'sides of said phase-shifting network a wave resulting from amplitude modulation of a carrier ofsaid given frequency with a difierent modulation frequency, wherebyduring some instants of-time one of said waves has a greater amplitude at said phase-shifting network than the in which other of said waves and during other instants of time the said one wave has less amplitude at said phase-shifting network than said other wave,

thereby causing the resultant waves received at said radiators to have different phase relations at difierent instants of time, and radiating the resultant waves received at said radiators.

13. In the production of a radio beacon through the agency of a pair of spaced radiators connected to the opposite sides of a phase shifting network, the steps of continuously supplying a wave resulting from amplitude modulation of a carrier of given frequency with one audio frequency signal to one of said sides of said network, continuously supplying a wave resulting from amplitude modulation of a carrier of said given frequency with another audio frequency signal to the other of said sides of said network, whereby during some instants of time one of said network than. theother and during other instants of time said one wave has a greater am.- plitude at said phase-shifting network than said other wave, thereby causing the resultant waves relations at different instants of time, and radiating .the resultant waves received at said radiators.

14. In a radio beacon, the combination which comprises a phase-shifting network having first and second sides, a source of carrier wavesconnected to said first and second sidesof said network, means continuously connected .between.

said source and said first side ofsaid network for modulating saidv carrier with an audio frequency signal, means continuously connected between said source andsaid second side of said network for modulating said carrier with a diftennas, and means for simultaneously produc-.

ing in said antennas voltages having a figure-ofeight field pattern whose major axis is in a line at right angles to the line joining the antennas.

16. An equi-signal radio beacon system com? prising two non-directional antennas spaced apart by a distance approximately equal to .one-.

half of the radiated wavelength, means for. ex-.

exciting said antennas in 180 outeof-phase relation with the other of said, signals to thereby produce two figure-of-eight shaped fields. each.

60 of which is respectively characterized byone of said signals and which overlap inspace to provide zones within which said signals are of equal intensity. 17. An equi-signal radio beacon-system comprising two non-directional antennas spaced apart by a distance approximately equal to onehalf of the radiated wavelength, means for exciting said antennas in in-phase relation with one of a pair of diiferent signals and meansfor simultaneously exciting said antennas in 180 out-of-phase relation with the other of said signals to thereby simultaneously produce two figure-of-eight shaped fields each of which is 75 characterized by one of said signals which overwaves has less amplitude at said phase-shifting received at said radiators to have difierent phase.

citing said antennas in in-phase relation with. one of a pair of different signals and means for lap in space to provide zones within which said signals are of equal intensity.

18. An equi-signal radio beacon system comprising two spaced non-directional antennas, a transmission line having inductive coupling to both of said antennas, a three winding transformer two of the coils of which are respectively connected in opposite branches of said transmission line, means connecting the mid-points of said coils to a source of radio frequency energy on which is impressed one of a pair of different signals whereby energy characterized by such signal is supplied in in-phase relation to said antennas, means connecting the ends of the third coil of the transformer to a source of radio frequency energy on which is impressed the second of said signals whereby energy characterized by said second signal is supplied in 180 out-ofphase relation to said antennas, whereby there are produced two figure-of-eight shaped fields each of which is characterized by one of said signals and which overlap in space to provide zones within which said signals are of equal intensity.

19. An equi-signal radio beacon according to claim 18, in which energy is alternately supplied to the first-named two coils of the transformer and then to the third coil thereof.

20. An equi-signal radio beacon according to claim 18, in which energy is simultaneously supplied to the first-named two coils of the transformer and to the third coil thereof.

FRANK G. KEAR.

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