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Sept. 3, 1946. H. a. BUSIGNIES 2,406,800 DIRECTION FINDER WITH FTLTER Fiied March 13, 1941 2 Sheets-Sheet l 3mm L .r if? m 7/s 9 6 .5.» . mmMW. ‘U H - F'! 6.7 5,444,’ cur- OFF ‘ / 086444701? FROM M455 l] .|$<T_._ INVENTOR. BY Patented Sept. 3, 1946 2, 6,80 UNITED STATES PATENT OFFICE 2,406,800 DIRECTION FINDER “71TH FILTER Henri G. Busignies, Forest Hills, N. Y., assignor to International Standard Electric Corporation, New York, N. Y., a corporation of Delaware Application March 13, 1941, Serial No. 383,111 11 Claims. (Cl. 250—11) I 2 The present‘ invention relates to radio direc tion ?nders and more particularly to direction ?nders having a pick-up member physically or effectively rotating at a constant angular velocity. a band pass or tuned ?lter rather than merely a brute force or smoothing ?lter of the untuned type. A local generator 1 is arranged to be driven by the same motor 3 which drives the goniometer 2. The outputs of this local generator 1 and of It is an object of the invention to provide an improved radio direction ?nder which shall be capable of being used over a wide range of fre the ?lter 6 are then combined in a suitable com quencies without critical readjustment of a num bining circuit 3 and used to produce an indica ber of separate antenna means while yet en tion in a suitable indicator 9. The combining abling a unidirectional indication to be obtained. 10 circuit 8 and indicator 9 may be of any suitable It is a further object to provide such a wide type. If the output of ?lter 6 is to be sinusoidal, range direction ?nder which shall give a direct which would be the case with all ordinary types reading unidirectional indication. . of ?lters and also with the ?lters shown in Figs. 3, 4 and 5, and if the output of the local gen erator ‘l is to be a series of Very brief contact It is a further object of the invention to pro vide an improved direction ?nder capable of giving a precise and unvarying indication of the closures (or openings), then the combining cir direction of arrival of radio waves, even though such radio Waves be keyed, modulated or even cuit 8 and indicator 9 may have the form shown in Fig. 6. As shown in this ?gure the sinusoidal interrupted for substantial intervals of time. output from ?lter 6 is separated into two sine The exact nature of my invention may best be 20 waves in phase quadrature by a phase splitter understood from the following detailed descrip tion taken in conjunction with the annexed drawings in which: Fig. 1 diagrammatically illustrates a radio di rection ?nder system embodying my invention. 5| and is thereupon applied to the de?ecting plates 64, 65 of the cathode ray tube 9' so as to produce a rotating ?eld. The brief circuit clo sures from generator 1, on the other hand, mo 25 mentarily drive the vacuum tube 52 beyond cut Fig. 2 is a series of related curves useful in o? thus producing momentarily high positive explaining the principles of my invention. Figs. 3, 4 and 5 illustrate di?erent forms of potential on accelerating electrode 63 of cathode ray tube 9'. As explained in my copending application, ?lters which may be used in the embodiment shown in Fig. l in accordance with a special fea 30 Serial No. 380,982 ?led Feb. 28, 1941, the effect ture of my invention. of this potential on electrode 63 is to produce a Fig. 6 illustrates one form of combining cir radial de?ection of the spot on the cathode ray cuit and indicator schematically represented in screen. Thus the indication given on the oath Fig. l, which form is suitable for use with ?lters ode ray screen has the form of a circle with a of the types illustrated in Figs. 3, 4 and 5. radial line extending inward from one point of Fig. '7 illustrates an alternative form of ?lter the circumference thereof toward the center. which may be used in accordance with a further Such radial line will not quite attain the center feature of my invention. but may be caused to approach thereto by the Fig. 8 illustrates a modi?ed system embodying application of suiiicient potential to electrode 63. my invention. ‘ Referring more particularly to Fig. 1 crossed loops la and lb are connected to a collector which is shown as a crossed-stator variocoupler of the type generally referred to as a goniometer driven by a motor 3 although it may alternatively be an electronic collector for performing an equivalent 40 Other forms of combining and indicating cir cuits may be substituted for the forms shown in Fig. 6. Thus, for example, if generator 1 be arranged to give a sine wave, the output from this generator may be connected to another phase splitter similar to phase splitter 6| of Fig. 6. Then the rotating ?elds from the two phase splitters (fed respectively from the output of function. The output of goniometer 2‘ is combined, if ?lter 6 and the output of generator 1) may be desired, with the pick-up from a non-directional applied to two sets of de?ecting plates so as to antenna lc, such combined wave is then ampli 50 produce ?elds rotating in opposite directions. ?ed and preferably also heterodyned and tuned The result will be an oscillatory non-rotating in receiver 4 and thereafter detected in detector‘ ?eld whose angle indicates the phase relation‘_ 5. The output of detector 5 is then passed through a ?lter 6 which in accordance with an ship between the wave from generator ‘I and the wave from ?lter 6. Thus, under the in important feature of my invention is designed as 55 ?uence of such oscillatory ?eld the cathode ray 2,406,800 3 spot will trace a line indicative of the direction of the received radio wave. Such an arrangement is described and shown in more detail in the copending application of F. Bac and me, Serial No. 23,966, ?led October 8, 1938, for “Systems for indicating the direc tion of propagation of electro-magnetic waves.” 1 See especially Figs. 3 and 4. In general, many 4 during which the incoming signal vanishes. For the present it will be most convenient to consider only that portion of the curves of Fig. 2 falling within the time interval WX. By virtue of the addition of energy from the non-directional antenna lo a curve which is shown in II should ideally be produced. A wave such as shown in curve II, corresponds to the well-known cardioid which is generally assumed cators may be used, in accordance with the 10 to exist when the output of a non-directional an tenna is combined with that from the goniometer present invention. Although the particular or other means having a rotating reception pat forms shown in Fig. 6 require sinusoidal output tern. As a matter of practical fact, however, from ?lter G and a sharp momentary pulse from ' different kinds of combining circuits and indi generator 1, whereas certain other forms require sine wave outputs from both the '?lter the ' it is difficult to adjust the relative strengths of the signal from'the non-directional and the sig nal ‘from the rotary ‘means so as to givefor all generator and still other forms require sharp wave lengths .a combined wave resembling that pulses for both outputs, all of such systems may shown in curve II. be used with the general system of Fig. 1 merely It may be thatthe ideal adjustment repre» by changing the local generator ‘I to fit the re quirements and by selecting either a ?lter giving 20' sented in curve II is attained for two or'threc a sinusoidal output or one of the special forms of ?lters shown in Figs.’ '7 and 8 which give sharp pulselike outputs. In direction ?nders wherein a rotation-mod ulated signal is detected before being used for giving an indication, it ‘has previously been sug gested to pass such detected faves through an ordinary smoothing ?lter, consisting of con Wave lengths within ‘the range but it will gener ally occur that at some wave lengths an ‘excess of non-directional energy will be .fed to the receiver giving a total input like thatof curve III. Like wise, at certain other wave lengths it will gen erally occur that the energy from the non-direm tional antenna lc will be smaller than the-energy from the effectively rotating pick-up means and will thus give a resultant wave such as shown in densers and resistors for eliminating the radio frequency component while retaining the low 30 curve IV. In order to avoid the occurrence of a wave such as shown in curve IV, it ‘would be frequency wave form substantially unaltered. necessary to provide elaborate adjustments for the antennae 105, lb and is or else ‘to normally ?lter In accordance'with 5 is provided which theis present of the general invention class of ?lters sometimes known as “tuned” ?lters in contract to the ?lters of the so-called “brute force” type. Such “tuned” ?lters are propor adjust the system so that at most wave lengths the energy receivedefrom antenna to was Very greatly insexcess of that required. Such excessive non-directional energy, however, is undesirable tioned with respect to a predetermined cut-off since the percentage of modulation produced by > frequency so'as to provide a very great discrim the effectively rotating. pick-up system is thereby ination between those frequencies lying above said cut-off and those lying below. Such ?lters .40 reduced thus reducing the accuracy of the direc tional indication. maybe of the low-pass type or of the band-pass In ‘accordance with the present invention the type and in some vcases may be merely tuned circuits, thus being capable of passing only a “tuned” type ?lter 6 is provided so as to enable single frequency. In all cases, ‘however, itis pro~ posed in accordance with my invention to design the-?lter 6 with reference to a particular fre quency determined by the rate of rotation of goniometer 2 or of the pick-up loop, if a rotat ing loop is used ‘instead of crossed loops and a goniometer. In general, it may be stated ‘that the ?lter is to be proportioned with respect to the frequency of effective rotation of the recep— waves such as those shown in curve IV to be em~ collector, or Whether it comprises a single loop If the output of the detector 5 is passed through a sharp “tuned” type ?lter 6, however, ployed even with inertialess indicating devices such as cathode ray oscillographs. The action of ?lter 6 is best shown in the two curves "J of Fig. ‘2. The sulting solid from line ‘curve detection V indicates of curve theIVwave withform simple smoothing to remove the radio frequencies. It will be clear that the form of this solid. line curve. is far from sinusoidal and is therefore wholly un suitable for passing through a phase splitter such tion pattern of the pick-up arrangement em as phase splitter .61 of Fig. 6. Likewise, such ployed whether this pick-up arrangement com form is also unsuitable for many other sorts prises Adcock antennae or crossed loop antennae 55 wave of combining and-indicating circuits. with some sort of rotating or e?ectively rotating which itself rotates. ' ' the wave form shown in the solid line curve V is It is preferred, moreover, that the ?lter '6 should have a su?iciently steep change in atten 60 changed to the ‘form’ shown in the dotted curve V. For the purpose of removingthe irregularities of uation with frequency so that a frequency one the wave form shown in the. portion WX of curves octave above the desired frequency will be sub~ V, it'is satisfactory to employ a ?lter capable of stantially suppressed. Preferably, too, the ?lter strongly discriminating against the second har should be designed so as to substantially suppress even those frequencies lying ten per cent. above 65 monic of the desired frequency. For some pur~ poses, however, it is preferable to make the ?lter and below the desired frequency. have a still sharper characteristic. > The advantage of using such a tuned ?lter In the case of keyed waves or waves which are having a comparatively sharp cut-oil can be ‘best interrupted for short periods by other means, explained by reference to the curves of Fig. 2. Curve I represents the output from goniometer 2. 70 it is highly desirable to arrange that the indi~ cations shall be constant in spite of the tem As is Well-known such output will be modulated porary cutting off of the Wave being measured. to such an extent as to involve phase reversal (schematically represented by alternate vertical and horizontal hatching). The time interval XY is assumed to correspond to a keying interval Thus, vreferring to Fig. 2 it is desirable that the dotted sinusoidal curve V should continue through interval XY even though the solid line 2,406,800 5 curve is shut off during this interval. In order to so continue the output of ?lter 6 it is merely necessary to proportion this ?lter so as to cut off the side bands which would correspond to 'pacity an output voltage may be obtained in the manner of a condenser microphone. Since the input is electromagnetic whereas the output is electrostatic direct coupling independent of the a modulation of the desired sine wave at the fork is minimized. f is a test winding which may be incorporated in a Hartley oscillator circuit to drive the fork for test purposes. Fig. 5 shows an arrangement similar to it but using a vibrating reed in place of a tuning it is merely necessary to proportion ?lter 6 so 10 fork. The damping factor of such reed can read as to strongly discriminate against the fre ily be adjusted thus varying the e?ective Q of the quencies of 20:5 (i. e., against the frequencies ?lter. 15 and 25) while still passing the desired fre Fig. 7 illustrates a ?lter arrangement adapted quency (20 cycles per second). to give pulselike peaks in place of sinusoidal If the ?lter is so proportioned, it will perform waves for the ?lter output. Such ?lter may be two separate functions: Not only will it remove used with combining circuits'and indicators of the harmonics of the desired wave and thus pre~ the form shown in Fig. 6 provided that local vent distortion as a result of the phenomena generator 1 is arranged to give a sinusoidal out shown in curves IV and V but also it will prevent put. In such case the connections from gener interruption of the ?lter output as a result of a 20 ator ‘! and ?lter 5 are merely interchanged so brief interruption of the incoming signal such as that the sine wave output of generator ‘5 is frequency corresponding to the time interval XY. If, for example, the time interval KY is 1/5 of a second whereas the desired frequency of the output of ?lter 6 is 20 cycles per second, represented by the interval XY. applied to phase splitter at of Fig. 6, whereas A third bene?cial result obtainable by the use of a “tuned” type ?lter 6 is that in the case of the peaked output of ?lter 6 is applied to tube 52. Referring more particularly to '7, an input speech modulated Waves or waves which are coil ab excites a vibrating reed V on the end of modulated by natural or man-made interfer~ ence, the directional indications given will be which is insulatedly mounted a conducting plate G. A pair of capacitative plates Pi and P2 are substantially as clear as if the modulations were mounted on either side of the rest position of con not present. Thus, for example, if the rotation ducting plate G. A high frequency from a suit rate of the rotary pick~up means is 20 per second and the ?lter 6 is arranged to discriminate able source S is applied to P! whereas a detector DI is connected to P2. When G occupies its rest strongly against the second harmonic and all position there is a substantial coupling between higher harmonics thereof, it is at once clear that P2 and Pi by way of element G and therefore voice frequency modulations, whose lower limit the output of such detector DI after ampli?ca is ordinarily not lower than 40 per second, will tion if necessary in the ampli?er H may then be be completely removed. delivered to output circuit CD for application to If the goniometer 2 is of the mechanically ro~ the combining circuit. tating type shown in Fig. 1, such goniometer will In operation the reed V is set in vibration by ordinarily be rotated at some rate of the order waves of the desired frequency across input ter of 10 to 50 rotations per second. in such case the 40 minals AB. As the reed passes through its rest frequency to be handled by ?lter 6 will be 10 to position, a momentary surge of high frequency 50 cycles per second if a non-directional antenna from oscillator S is coupled through member G such as to is used, or will be 20 to 100 cycles from plate PI to P2 and after recti?cation in de per second if such non~directional antenna is tector D! and ampli?cation in H produces a brief omitted and a bilateral indication is to be given. pulse at output terminals CD. Such brief pulse In either case, however, it is clear that the fre occurs twice per complete cycle of reed V at the quencies in question are so low to make it ex moments of passage of this red through its cen pensive to provide ?lter elements of reasonably tral position. A bilateral indication will there high Q and therefore in accordance with. a parfore be given even though the input to AB be so ticular feature of the present invention it is pro derived from a system employing a sensing an posed to employ electromechanical filter means tenna such as 10 of Fig. 1. for use in connection with direction ?nders em~ In order to avoid sensing ambiguities addi ploying actual rotation of some mechanical mem tional plates P3 and P4 may be provided, plate P4 ber for producing the required effective rotation. being connected in parallel with plate Pl while of the reception pattern. t should be noted, plate P3 may be placed in parallel with plate P2 however, that in cases where the eifective rota by means of a switch. When plate P3 is con tion of the reception pattern is produced electron nected, an extra pulse in addition to the two brief ically ordinary conventional electrical ?lters may pulses per cycle which have been above described conveniently be employed. will be given during the time when the reed is at Figs. 3, 4 and 5 illustrate preferred forms or‘ 80 the right-hand extremity of its swing. Such ex electromechanical ?lters to be used with ‘ dio tra pulse will be easily distinguishable from the direction ?nders having mechanical rotation. two pulses previously mentioned by virtue of its In Fig. 3 there is shown a tuning fork used for greater duration. This extra pulse being dis coupling together two coils cd and ab. Prefer~ posed at 90° with respect to the two short pulses ably, the fork is permanently magnetized. and is above mentioned will serve to indicate which one driven by ?eld from input coil oh, the opposite of these short pulses represents the true direction tine of the form then serving to deliver energy of the incoming waves. to output coil cd of the ?lter arrangement. Fig. 8 shows a modi?ed system wherein the pas Fig. 4 shows an improved form wherein electro sage of a light beam through aligned openings is static output coupling is employed to void pose 70 made use of to replace the electrostatic coupling sible direct action between the input and output of Fig. '7, Whereas the simple rotating pointer 9" independent of the fork. In this figure a capaci' illuminated by such light beam replaces the cath tor plate adjacent to the output tine of the fork ode ray tube 9' of Fig. 6, as well as generator ‘1. varies the capacity output terminals CD. By Referring more particularly to Fig. 8 pick-up applying a suitable polarization across such ca 75 means la, lb, I c, 2 and motor 3 are substantially 2,406,800 7 . '8 as in Fig. 1 whereas receiver and detector 4 and inating strongly against frequencies ten per cent. 5 have been combined under a single apparatus 45. above and below said predetermined frequency. For ?lter '6 there is provided reed V excited by a coil connected across AB substantially as in Fig. '7 but instead of bearing a conductive coupling mem ber such as G this reed V bears a shutter T pierced by a small opening. A light source LS projects a light through the small opening of T and through an aligned opening in another shutter 3. A radio direction ?nder comprising pick-up means effectively rotating at a predetermined frequency for picking up signals modulated at said frequency by virtue of such rotation, further T2 to illuminate the rotating pointer 9” which means for non-directionally picking up signals and adding them to said signals modulated at said frequency to yield resultant signals whose en velope curve contains a component of said pre determined frequency, means for detecting said resultant signals, an indicator controllable by sinusoidal waves, a mechanically vibratory, mem~ ber having a natural frequency substantially is rotated by motor 3. Since the light beam can only pass through the openings T and T2 when V is in its central or rest position the pointer will be illuminated only for two brief instants during each cycle of the vibration of the reed V. 15 equal to said predetermined frequency, means for setting said member into vibration under con Due to .the persistence of vision therefore a trol of said detected signals, and means for de pointer will be seen as standing stationary in two livering sinusoidal waves to said indicator in re positions 188° apart. A suitable graduated scale sponse to vibrations of said member. GS placed in proximity to the pointer 9" serves 4. A radio direction ?nder comprising pick-up to facilitate direct reading of the direction to .20 means effectively rotating at a predetermined be indicated. In order to avoid sense ambi— frequency for picking up signals modulated at guities an auxiliary shutter Tl may be pivotally said frequency by virtue of such rotation, fur mounted so as to cut 05 the beam’s light except ther means for non-directionally picking up sig~ when de?ected by a sensitive meter movement M. A photocell F is then arranged to actuate 25 nals and adding them to said signals modulated at said frequency to yield resultant signals whose the meter movement Min response to illumina envelope curve contains a component of said tionand this photocell so positioned as to be predetermined frequency, means for detecting come illuminated momentarily each time that the said'resultant signals, an indicator controllable shutter T is withdrawn to its right-hand position by the vibration of reed V. 30 bysharp electrical pulses, a mechanically vibra tory member having anatural frequency substan If the meter movement M and associated shut tially equal to said predetermined frequency, ter Tl are arranged to have a suitable operating means for setting said ‘member into vibration time it will then result that when the reed V under control of said detected signals, and means reaches its extreme right-hand position the meter for delivering sharp electrical pulses to said indi movement will commence to be energized and the cator in response to vibration of said member. resulting withdrawal of shutter T! will be com 5. A radio direction ?nder comp-rising pick-up pleted at about the time when the openings in means effectively rotating at a predetermined fre shutters TI and T2 become aligned during the quency for picking up signals modulated at said succeeding half cycle. Thus when reed V passes through its central position while moving from 40 frequency by virtue of such rotation, further means for non-directionally picking up signals right to left the beam of light will be momen and adding them to said signals modulated at said tarily permitted to fall upon pointer 9". Therm frequency to yield resultant signals whose en after during the time’ when the reed V travels velope curve contains a‘component of said pre from its central position to its left-hand position and back the shutter Tl wlil return to normal and 45 determined frequency, means for detecting said resultant signals, an indicator controllable by block the passage of the light so that no illumi brief flashes of light, a mechanically vibratory nation will be provided at the instant when the member having a natural frequency substantially reed, V passes through its central position from equal to said predetermined frequency, means for left to right. 50 setting said member into vibration under con What I claim is: trol of said detected signals, and means for me 1. A radio direction ?nder comprising pick-up chanically controlling the passage of brief flashes means effectively rotating at a predetermined fre of light to said indicator in response to vibration quency for picking up signals modulated in ac of said member. cordance with such rotation, means for detecting said signals, means for non-directionally picking 55 - 6. A direction ?nder according to claim 4 wherein said means for delivering sharp elec up signals and for adding them to said signals trical pulses comprises means for deriving oscil~ modulated in accordance with said rotation whereby the resultant signals after detection con tain a component of said predetermined fre lations of a frequency high in comparison with said predetermined frequency, means for cou quency, indicator means for giving a directional 60 pling said oscillations to an output circuit in a indication under the control of such detected sig nals, means for applying said detected signals to said indicator means, and a tuned ?lter propor tioned to pass said predetermined frequency while sharply varying manner under control of the vibrations of said member, and means for deliver- ing to said indicator such coupled oscillations. 7. A direction ?nder according to claim 5 discriminating strongly against frequencies ten 65 wherein said means for delivering sharp elec~ trical pulses comprises means for deriving os~ per cent above and below said predetermined fre oillations of a frequency high in comparison with quency before application to said indicator means. said predetermined frequency, means for cou 2. A direction ?nder according to claim 1 fur pling said oscillations to an output circuit in a ther comprising means for non-directionally picking up signals and for adding them to said 70 sharply varying manner under control of the signals modulated in accordance with said rota tion whereby the resultant signals after detection contain a component of said predetermined fre quency, and wherein said ?lter is proportioned to pass said predetermined frequency while discrim~ 75 vibrations of said member, means for detecting the oscillations coupled to said output circuit and means for delivering to said indicator such detected oscillations. 8. A radio direction ?nder comprising pick-up 2,406,800 means e?’ectively rotating at a predetermined fre quency for picking up signals modulated in ac cordance with such rotation, means for detect ing said signals, indicator means for giving a directional indication under the control of such detected signals, means for applying said de tected signals to said indicator means, and a tuned 10 10. A radio direction ?nder comprising pick-up means eifectively rotating at a predetermined fre quency for picking up signals modulated in ac cordance with such rotation, means for detect ing said signals, indicator means for giving a directional indication under the control of such detected signals, means for applying said detected signals to said indicator means, and a tuned ?lter proportioned with respect to said predetermined ?lter proportioned with respect to said predeter mined frequency for ?ltering said detected sig nals before application to said indicator means, 10 frequency for ?ltering said detected signals, be comprising a mechanically oscillatory member fore application to said indicator means, com having a natural period of vibration, input means prising a mechanically oscillatory member hav for setting said member into vibration under con~ ing a natural period of vibrations, input means trol of said detected signals, and output means for for setting said member into vibration under con in?uencing said indicator means under control of 15 trol of said detected signals, and output means the vibrations of said member. for delivering brief ?ashes of illumination to said 9. A radio direction ?nder comprising pick-up indicator means under control of the Vibrations of means effectively rotating at a predetermined said member. frequency for picking up signals modulated in 11. A radio direction ?nder comprising pick-up accordance with such rotation, means for de 20 means effectively rotating at a predetermined fre tecting said signals, indicator means for giving quency for picking up signals modulatively rotat a directional indication under the control of such ing at a predetermined frequency for picking up detected signals, means for applying said de signals modulated in accordance with such rota tected signals to said indicator means, and a tuned tion, means for detecting said signals, indicator ?lter proportioned with respect to said predeter 25 means for giving a directional indication under mined frequency for ?ltering said detected sig the control of such detected signals, means for nals before application to said indicator means, applying said detected signals to said indicator comprising a mechanically oscillatory member means, and a, tuned ?lter proportioned to pass having a natural period of vibration, input means said predetermined frequency while discriminat for setting said member into vibration under con~ 30 ing strongly against frequencies ten percent above trol of said detected signals, and‘ output means and below said predetermined frequency. for delivering brief electrical signals to said indi cator means under control of the vibrations of HENRI G. BUSIGNIES. said member.