US2736022A - Kramar - Google Patents

Description

E. KRAMAR RADIO BEACON Feb. 2l, 1956 3 Sheets-Sheet l Filed June '7, 1951 INVENTOR Ernst Kram ar ATTORNEY Feb. 21, 1956 I E, KRAMAR 2,736,022 RADIO BEACON Filed June 7, 1951 3 Sheets-Sheet 2 INVENTOR. 5,718? Kramar Feb 21, 1956 E. KRAMAR l 2,736,022

RADIO BEACON Filed June 7, 1951 3 Sheets-Sheet 3 Fig. 5

IN V EN TOR.

Erna? Kramar I fdirection isdetermined by'the elapsed time between ynorth identification and the passing of the minimum .through the receiving equipment, measured at the posi- Ation bymeans of astop watch. However stop Watch lmethods.areirnpractical and have the disadvantage that .a.cornplete.revolution ofthe beamed radiation has to .important -for ship :navigationl place ,of .thecommon light beacons, or in addition thereto, .especially .when visibilityis poor.

.to .the .minimum .position .respecttoa Vxeddirection in the revolving radiation,

United States l2,736,022 .RADIonEACoN vErnst KramarfPforzheimyGermany, assigner to linternational -Standard'Electric Corporation, New York, N Y., a corporation of Delaware Application June '7, 1951, Serial No. 230,298 Claims priority, application. Germany June 9, 1954) 6 Claims. (Crew- 106) There are known radio beacons with a rotating directional pattern having a single or multi-leaved beam radiation with outstanding minima. `When these minima pass through a predetermined directiomfor instance north, a particular non-'directive,identification is sent out. The the be completed before a determination of direction is possible.

Such rotating radio beacons are, among other things, V,They can be used in Ithas .already .been suggested to avoid the stop watch measurement by announcing the direction corresponding ofthe directional beam with when arevolving radio beacon with rotating minimum of .a directional ,radiation is used. Such beacons, for instance, may Vcomprise a directional antenna system 1n .conjunction withanon-directional antenna. The directive diagramis modulated withaudio frequency, andthe radiation. ofthe directive diagram interrupted at times, in order that the identification can be sent over the omni- ,directionalaerial during the pause.

,modulation of .the revolvingbeamed radiation, and that the -direction.corresponding to the minimum position of this directive radiation is continually announced over thetransmitting system. According to the described example a rotating directive diagram is periodically Y changed in its position in a fast rhythm in comparison to the,rotatingA frequency, during rotation, whereby two rotating directive diagrams alternately result, and the direction .corresponding to the equal signal value of both ,diagrams isannounced over .this Vdirective radiation system.

In completing the ideaof this invention it is further suggested that the rotating radiation system is supplied by the .transmitter modulated .with the identification announce- 'ment andinV addition. thereto, supply a push-pull device with the co-phasal output voltage of the sender which .is controlled anti-phasally by the phase modulation (of anV audio4 frequent keyfrequency), whereby the output of thepush-pulldevice supplies a rotating directive aerial system, .i..-e. .the radiation of which having a distinct minimum (i. e. v.an 'S-formed Acharacteristic which, in conjunction with'afurther radiation of the same freatent "O transmitter which operates Yqueucy lgives a cardioidshaped diagram). Two tubes which are alternately blocked, can be advantageously .used as a phase modulation push-pull device, the grids .of which are supplied co-phasally with the high frequency voltage of the transmitter modulated with the identication announcement.

it is often desired that a ne sub-division be accomplished in addition tothe coarse Vdivision of the region around the rotating beacon having at least two sectors.. `When a light beacon is used it is appropriate to mark thesections with the colors greenand red and totiuely divide by means of digitswhich correspondvtotheiangle of fixed 'direction for`instance north. In orderto fix a position during a first revolution the section is announced and during a second revolution the exact angle is announced. If it is desired to operate several rotating radio beacons with the same wave length along a shore strip, then, according to the invention the individual beacons radiate one Vafter the other changed inacertain rhythm. During a denite period of time only one beacon radiates and rotates as Vdescribed above.

Figure l is a schematic circuit diagram illustrating the radiobeaconshowing one` example of. my invention, and Figures 42 through 5 are diagrams illustrating the operating principles of a radio beacon in accordance with this invention.

lThe invention will iirst beV broadly described inconnection With Figure 1. The character S represents a lwithl any desired wave: length. it is modulated by an identification which has a word, a digit ora letter assigned-to each direction by signals'from source 3 incomparison to'a referencen direction. 'The output voltage Aof the sender is supplied to an omni-directional aerial 5 on the one hand which continually radiates the identification and on the other hand co-phasally to the two push-pull tubes R1 and R2. The twotubes'are further anti-phasally controlled by aV phase modulation voltageover the transformer T1, from 'a switching source 6 the frequency of which' is higher than therotating frequency of thedirective radiation. Under certain-conditions it could be practical-not to give this control voltage a sine form but to adapt ity more or less'to `a rectangular or trapezoid form; The condensers C1 and C2 respec- -tively chokes D1 andiDz serve to mutually bloclcthe' high frequency and modulation circuits. Between the center of the transformer T1 andthe connectedcathodes of the tubesthe grid voltage Gis presentg'between the center of the output transformer and the cathodes,the anode voltageY A is present. The output transformer T2 supplies a directive aerial 1, v2, 3, 4, system'in-such a manner, that the direction of current alternates corresponding to the rhythm of modulation. In the most` simplecase the directive aerial system may consist of a rotatable frame or simply the two radiators' l and 2, which is mechanically driven. By way of illustration, antennas 1-'5 are shown as mounted on rotatable disc 7. The rotation of the directive aerial system and the proper announcement of the identication must take place synchronously. The motor 9 is shown coupled by shafts l0 and'll torsignal source 8 and disc"7 as indicated. This-shows Van example of mechanical rotation of the antennasfsimultaneously with the-control of' the signal. The identification can be recorded on a disk, a film-or steel band which is synchronously drivenwith the directive aerial system.

Operation of the arrangement is as follows: By interaction of the directive aerial system and the omni-directional aerial a cardioid radiation characteristic results in a manner already known. By means of rhythmic switching over the'push-pull tubes caused by phase modulation two mirrored cardioid diagrams result. The ntersection ,points of both diagrams fix the bearing raydeiined by an equal signal value of both radiations. It rotates with the desired frequency of the rotating radio beacon. The identification announcement can be clearly heard in the bearing direction. in other directions the key frequency (phase modulation) is noticeable as an interfering modulation in the head set or loud speaker so that the identification is distorted or completely undetectable. In order to differentiate between the individual rotating radiation beacons it is suggested in the invention to announce the identification name of the radiation beacon for example Bill For this purpose the phase modulation is interrupted particularly when the bearing ray passes through a predetermined direction such as north, east, south and/ or west.

The disadvantage of this method its ambiguity as two minimum values of the interfering modulation occur, spaced 180 degrees. The drawback of ambiguity may be eliminated by the following method.

The method in accordance with the further invention described above is in is characterized by the feature that a directional pattern having but one distinct minimum over a S60-degree range is modulated stepwise by a phase angle less than 90 under its rotation at a rate high with respect to the frequency of rotation and preferably within the audio range, so two patternsV are obtained which intersect between the minimum points of either diagram, and that the direction corresponding to a minimum of interfering modulation at the crossover point of the switched patterns is modulated continuously on the carrier frequency of the directional radiation as a varying identification.

The pattern-switching causes in the receiver an interfering modulation which however disappears at the crossover point of the two diagrams as much as with dot-dash or A-N keyed localizers. In this manner the known method where directions are determined by the absence of the directional radiation or the modulating tone of a rotating cardioid-like pattern is extended into a method where the direction is determined by the disappearance of an interfering modulation, i. e. an audio frequency as well, While however unlike the so far known methods a carrier signal is left in the direction of minimum interfering modulation.

The directional antenna array is further provided with an identification correlated with the respective azimuth position of the interfering modulation which continuously indicates the sequence of azimuth positions. The azimuth identification is clearly audible only in the absence of interfering modulation while in all other azimuth directions it is disturbed by the interfering modulation.

In Figs. 2 through 5 the method is illustrated in detail. By means of a directional antenna array which for example comprises four outer radiators at the corners of a square and a center radiator with their feed phases so chosen that each of the two sets of diagonally opposite antennas has its two antennas out-of-phase to each other, while the two sets of antennas are fed in phase quadrature. The phase of the center radiator is chosen equal to that of one of the outer antennas. A rotating R.F. iield is set up the radiation pattern of which is much similar to a cardioid in that it dips to a sharp minimum. This pattern can be rotated either mechanically by turning the whole antenna array, or electrically by means of goniometer equipment. In accordance with the invention, the currents feeding the antennas are modulated stepwise in their relative phases in a way that the radiation pattern set up at a given set of phase conditions is switched back and forth at a rate high with respect to the speed of rotation through an angle less than 90, for example 30. This gives rise alternately to the radiation patterns marked A and B in Fig. 2 which intersect at point S. lf patternswitching is effected at an audio rate, an audible interfering modulation is caused in the receiver which disappears only at the crossover point and in the region where the two diagrams cover up. Upon proper choice of the radiation pattern, i. e. in a way that the two alternatiugly keyed patterns cover each other in the region opposite to the minimum, no further crossover will result.

This particular radiation pattern where to al1 practical purposes the cardioid-like pattern is circular in the region opposite to the minimum, can be attained by proper choice of the relative current intensities feeding the individual radiators of the directional array. If, for example, two opposite outer radiators are fed with unit current intensity, the center radiator with an intensity of two units, and the two remaining opposite radiators with an intensity of V 3 units, this will result in an elliptic rotating iield and a radiation pattern which everywhere except at its minimum comprises contour lines which are virtually circles.

The production of an elliptic rotating field is illustrated in Fig. 3. The parts l, 2, 3, 4 and 5 are individual radiators comprised in the directional system. The opposite outer antennas Il and 2 are fed at opposite phases with unit intensity, while the opposite outer antennas 3 and 4 are also fed out-of-phase, but at an intensity of V3 units and the center antenna 5 is fed with an intensity of two units in phase quadrature to three of the outer radiator units. This feed scheme will cause an elliptic rotating field D and a radiation pattern K, the contour lines of which are virtually circles in the region opposite to the minimum.

Fig. 4 shows the alternately keyed patterns in rectangular coordinates under the assumption that the directional array is fed in the manner outlined above and that pattern switching, or stepwise feeder phase modulation through i30 is carried out. Here A represents one, and B the alternate radiation pattern which intersect at point S, and also at the points s1, s2, s3. At all of these crossover points the interfering modulation caused by patternswitching will disappear with curve C illustrating the amplitude of the interfering modulation signal. As is apparent, the interfering signal increases strongly near the desired bearing beam S.

As, at the transmitting end the directional pattern is rotating, the pilot of an aircraft will observe first a heavy increase in the interfering modulation followed by absence of the latter near the rotating bearing beam which makes the identifying modulation clearly audible. Once the bearing beam has passed, the interfering modulation will increase again followed by a decrease. At points s1, s2, s3 the interfering modulation will indeed disappear too, and the identifying modulation will be audible also over the range to 230, but this will introduce little trouble with an omnidirectional range, as the bearing beam proper is defined by its accompanying strong interfering modulation at either side, and confusion will hardly be possible with the relatively large angular range 70 to 230, the less so as the identifying modulation varies steadily throughout this range where it is distinctly audible.

As the two patterns A and B are identical, the spurious bearing beams s1, s2, s3 can be entirely eliminated, if pattern-switching in the mentioned embodiment is done with L55 This condition is shown in Fig. 5 which illustrates that only one crossover point S of the two patterns is left. It is true that between the angles and 150 the interfering modulation will disappear as well, butas outlined abovenobody will mistake this range for a bearing beam.

lt should be clearly understood, that this description is made only by way of example and not as a limitation to the scope of my invention as set forth in the objects and in the accompanying claims.

`tit/hat is claimed:

l. An omnidirectional radio beacon comprising means for radiating energy in a directive pattern having a null point, means for effectively rotating said pattern at a predetermined speed, means for transmitting signals indicative of the direction of said null point in synchronization with said effective rotation, and means for alternately shifting the phase of energy in said directive pattern at a rate relatively high with respect to said predetermined speed, whereby said signals will be obscured by the phase modulation of said phase shift, except in the direction of said null point.

2. A radio beacon comprising means for radiating energy comprising a rotatable directive radiator, and an omni-directional radiator, a source of radio frequency energy, means for alternately shifting the phase of said radio frequency energy at a rate high with respect to the speed of rotation of said radiator, means for applying said alternately phase shifted energy to said directive radiator, a source of direction indicating signals synchronized with said rotation of said directive pattern, means for modulating energy from said source with said signals, and means for applying said modulated radio frequency energy to said omni-directional radiator.

3. A beacon according to claim 2 wherein said means for shifting the phase of said energy comprises, a pushpull device, means for applying said radio frequency energy to said device in parallel, means for applying a phase shifting signal to said device in parallel, and means for extracting energy from said device in push-pull.

4. A radio beacon according to claim 2 wherein said rotatable directive radiator comprises four radiators, positioned at the corners of a square, and said omnidirectional radiator comprises a radiator positioned at the center of said square, further comprising means for applying current to respective pairs of diagonally opposite radiators, and said center radiator, in the ratios of References Cited in the file of this patent UNITED STATES PATENTS 2,129,094 Greig Q Sept. 6, 1938 2,212,233 Kolster Apr. 20, 1940 .2279.931 Cocker-ell et al. Apr. 7, 1942 2,303,0 l9 Morawetz Jan. 12, 1943 2,424,079 Dome July 15, 1947 2,513,493 `Kliever July 4, 1950 2,578,961 Aribert Dec. 18, 1951 FOREIGN PATENTS 467,9 t3 Great Britain June 9, 1937 114,495 Australia June 24, 194() 866,707 France May 31, 1941 960,186 France Oct. 17, 1949

Images