Патент USA US2406406код для вставки
- Aug. 27, 1946.4 P. c1. sANDRET'ro ET AL 2,406,406 RADIO DIRECTION FINDER Filed July 24, 1941 » 4 Sheets‘Sheet 1_ QN @Zay ’ff Aug. 27, . A1946. P. c.~ sANDRETTo ET_AL 2,466,406 RADIO DIRECTION` FINDER Filed JùIy 24, 1941 4 Sheets-Sheet 2 è. N< < xm. @za/CJ @ff/M, M Allg- 27, 1945- P. c. sANDRET-ro E-rAL , 2,405,406 RADIO DIRECTION FINDER Filed July 24. 1941 4f Sheets-Sheet 4 ma; r Patented Aug. 27, 194s UNE'E'E 2,465,406 STATES PATENT @ENCE 2,406,406 RADIO DIRECTIÜN FINDER Peter C. Sandretto, Chicago, and Elmer P. Buck 'thai, Brookiield, Ill., assignors to United Air Lines, Inc., Chicago, Ill., a corporation of Dela War@ l Application July 24, 1941, Serial No. 403,5502 17 Claims. (Cl. Z50-11) This invention relates to radio direction ñnd ers, more particularly to ground station radio direction finder systems for use at medium high frequencies, and the invention has for an object the provision of improved systems and apparatus i this character. Radio direction finders utilizing antennas hav ing directional sensitivity are of course known in the art, the usual practice being to employ 2 antenna arrangement, and selective means for connecting the two loop antennas in opposed parallel relation to suitable receiving means, or for connecting one of the loop antennas and the vertical antenna in parallel relation through a suitable coupling means or phase shifter to the receiving means. The output of the receiving means, which pref erably includes one or more fixed frequency oscil two or more ground station direction ñnders 10 lators adapted to beat together with the carrier supplied to the receiving means from the an tennas, is connected by way of a rectifier to sen determined, whereby bearings may be obtained sitive instrument means having a movable ele simultaneously at each station, and the position ment adapted to trace a permanent record on a tuned to the carrier frequency of the transmitter on an airplane or ship whose position is to be of the plane or ship located by triangulation. The medium high frequencies presently available for aircraft transmitters, however, are propa gated by the ionosphere, and difficulties in ob taining accurate bearings at such frequencies have been encountered due to the various distor tions and errors which are interjected by this propagating medium. constantly moving recording surface. In order properly to orient the continuous record of signal intensity thus produced with respect to the com pass position ci the antenna arrangement, a switching device is provided associated with a 20 rotating part of the antenna arrangement and connected in circuit with a second movable record tracing means, so that the recording surface will Examples of some of the errors recognized by receive periodic indications of the relative posi the art as occurring in radio direction finders tion of the antenna arrangement from which the operating at such frequencies, and as to which 25 continuous record of the signal intensity may be various corrective attempts have been made, are properly oriented. observational errors due to fading and to the The present invention also includes within its difîiculty oí" distinguishing between a “crisp” null scope the provision of means for rendering the and a “hollow” null, deviation errors caused by output frequency cf the receiving means inde minute-by-minute and second-by-second varia 30 pendent of the carrier frequency supplied to the tions in the ionosphere, polarization errors due receiving means by the antenna arrangement, as largely to horizontally polarized sky waves, and well as automatic means for controlling the re the various errors due to the presence of static. spective connections of the loop antennas and In spite of all corrective attempts which have the vertical antenna to each other and to the heretofore been it is a well recognized factk 35 receiving means, whereby accurate records may that the bearing errors which occur even with be obtained free from the usual bearing am best equipment heretofore known, may be of biguity and substantially uniniiuenced by static magnitude as to render substantially useless conditions. In addition, means may be provided bearings taken even by skilled operators. for insuring a constant phase displacement be It is accordingly a further object of this inven 40 tween the energy input from the vertical antenna tion to provide a radio direction finder system and loop antennas, regardless of the carrier fre for medium high frequency work capable of elim quency, and if desired automatic volume control inating, correcting or minimizing substantially means may be employed so as to render the con all ci the known and recognized errors, and of tinuous records obtained from the improved sys substantially automatically providing permanent 45 tem independent of variations in the intensity records of individual bearings of such character of the carrier. that unskilled operators may readily determine, For a more complete understanding of this by mere inspection of any group of records, the invention, reference should now be had to the true bearing of the transmitting station. accompanying drawings in which: In carrying out the invention in one form, a 50 Fig. 1 is a somewhat diagrammatic representa rotatable antenna arrangement is provided com tion of the circuit connections and the various prising a pair of spaced loops arranged in coaxial operating parts of a radio direction finder em relation and a vertical non-directional antenna bodying the present invention; coincidentl with the axis of rotation, together Fig. 2 is an illustrative circuit diagram of a with means for constantly rotating the entire 55 portion of the system shown in Fig. 1, which is 2,406, 406 3 4 be further described hereafter and which is rep adapted to eliminate or minimize the eiïects of resented in Fig. 1 diagrammatically and indicated by the reference numeral 31. The oscillator static on the continuous bearing records ob tained; means 3l beats with the carrier of the received signal, and produces at the output of the radio Fig. 3 is a circuit diagram of an automatic means for controlling the antenna connections selectively to produce a cardioid pattern in order to remove the bearing ambiguity; Fig. 4 is a circuit diagram of a somewhat modi fied arrangement including means for insuring receiver 29 a beat note of predetermined fre quency, the output being connected by suitable conductors 38 to a band-pass filter 39 capable of passing the beat note frequency. The iîlter Y39 is connected, as shown, to a rectiñer 4Q which 10 constant phase Shift between the respective in-Y Vis illustrated as comprising a suitable transformer puts of the loop antenna and the vertical an 4I and a full wave rectifier tube of the duo-diode tenna, regardless of the frequency of the com mon carrier to which the respective antennas are The output of the rectifier 4t is connected by tuned; . the conductors/13 With the Winding 44 of sensi Fig. 5 is a circuit diagram of a still further tive instrument means comprising a milliam modification, including automatic volume control meter which is illustrated as including, in addi means which will prevent overloading ’of the Y tion to the coil 44, a permanent magnet 45 hav receiving means and correct for fading Y_signals _ , ing an air gap Within Ywhich the moving coil is without being detrimental to the accuracy of the> mounted for rotation. Carried by the moving 20 direction iinder system; and coil 44 is a suitable tracing element 41 which Figs. 6, “7, and 8 are illustrative bearing records may include a suitable ink supply, not shown, which may be obtained under certain conditions and which is arranged to record the rectiñed out in the operation of radio direction finder systems put of the receiver on a chart or recording sur embodying this invention. A ' face 48. The chart 48 is preferably carried, as Referring now to Fig. 1, the invention is illus 25 shown, on a rotatable drum 49 which is driven trated as embodied in a radio direction ñnder at a constant speed by a suitable motor 50, the having rotatable antenna means comprising a motor 50 being so synchronized with the driving pair of spaced apart shielded loop antennas IEI motor of the antenna arrangement contained in and II, which are mounted in coaxial relation the base I5 as to insure that the chart 48, which 30 on opposite ends of a horizontally extending beam is graduated in the usual fashion to indicate dee I2 secured for rotation on the upper end Vof a grees of movement, will move through a distance rotatable post I3, the beam I2 and the post I3 corresponding to 360° during each complete revo being shown in broken lines since the mechanical lution of the antenna arrangement. Thus it will structure of these elements constitutes no part be seen that an ink trace, such as indicated by of the present invention. Intermediate the loop 35 the reference numeral 5I in Fig, ‘1, will be pro antennas’lú «and II and mounted coincident' with duced on the chart 48 so as to provide a per the aXis of the post I3, is a vertical antenna I4. manent record of the signal intensities supplied and the entire antenna arrangement is mounted to the receiver 29 during rotation of the antenna on a suitable base I5 containing a drivingl motor arrangement. ' 40 and suitable gearing (not shown) for rotating the ‘In order properly to orient the ink traces on post I3v and the parts mounted thereon at a pre determined constant speed. As' shown, the loop antenna I0 is connected by suitable transmission vlines I6 and YI'I to a pair of slip rings I8 and I9, respectively carried the chart 48 with the compass position of the antenna means, the rotatable post I3 of the an tenna arrangement is provided with switching 45 means including a rotating Contact 52 which is by the rotatable post I3 and adapted to be en gaged by suitable brushes 20 and 2l. Similarly, the loop antenna I I is connected by transmission lines 22 and 23 to the slip rings 23a and 24, re spectively'carried by -the post I3 and adapted to be engaged by brushes 25 and 26 respectively. The brushes 2U and 2|, which are associated as above described with the loop antenna I (l, are permanently connected by means of suitable _con ductors 21 and 28 to the input of a radioreceiver ' 29 which may be of the conventional type hav ing the usual detectors, radio frequency ampli ñers, intermediate frequency amplifiers, audio output, andV necessary interconnections. YThe adapted to engage a co-operating stationary con tact 53 once during each revolution of the an-tenna arrangement. This switching means is connected, as shown, in circuit with a battery 54' and the energizing winding 55 of a relay, so that each time the contacts 52 and 53 close, the armature 555 of the relay will be attracted and a suitable tracing element 51, which is 'carried by the armature 5B, will be operated to trace on the chart 48 a reference mark, such for example as the mark 58, which may be used to orient the ink trace 5I with the compass position of the antenna arrangement. For example, if the ref erence mark 58 corresponds to a true north-south position of the antenna loops IB and I I, the rela brushes 25 and 26, which are associated as above 60 tive compass positions of the various maximum described-with the loop antenna I I, are per and minimum intensity points indicated by the manently connected to the stationary contacts trace 5I may readily be determined. 30 and 3l of a multiple pole double throw switch While various other antenna arrangements ing or coupling means 32, and it will be observed known to the art, such for example as the Adcock that when the switch is thrown to a left-'hand antenna system connected to the receiver by position, as viewed in Fig. 1, the loop -antenna II will be connected through the contacts 3Q -and 3I , means of a goniometer, may be utilized within the broad principles of this invention, the particu lar antenna arrangement illustrated in Fig. l has circuit of the loop antenna I0, the connections 70 been found highly advantageous in eliminating polarization errors which may arise due to‘the being such that the two loop antennas _are con presence of horizontally polarized sky waves. ' nected to the input of the receiver 29 in opposed When the antenna arrangement shown in Fig. parallel relation. ` l occupies a position such that the beam I2 is Associated with the receiver 29 is a suitable oscillator means of fixed frequency, which will 75 pointing directly at the transmitter station, a the switch blades 33 and 34, and the conductors 35 and »3s to the 'conductors 21 and 2a in the 2,406,406 5 vertically polarized ground wave will of `course induce equal' and‘opposite voltages in the two sides of each of the loop antennas, and no signal will be supplied to the receiver 2t from the an tenna arrangement. Likewise, when the beam i2 is at right angles to the direction of the trans mitter, a vertically polarized ground wave will induce maximum voltage in each of the coaxially mounted antenna loops, hut since these antenna 6 antenna 64a. is connected in parallel with the loop antenna â il through the switch blades 33 and 34 in order to prevent unbalance of the system, in addition the vertical antenna is connected through the knife blade ÈB, the switch Contact 34, a conductor a phase shifter or coupling means E6, which is shown diagrammatically in Fig.Y 1, and by way of conductor El to the receiver Ztl. The coupling means or phase shifter 66 in~ loops are connected opposed parallel relation, 10 sures that the energy received from the vertical zero signal intensity will again be supplied to the antenna I4 will be displaced 90° from the energy receiver. Accordingly. with a substantially en received from the loop antenna it so that the well tirely vertically pclariz. . wave. four nulls will known cardioid pattern will be produced. occur during'each revolution of the antenna ar ri‘hus, in order to obtain a continuous record rangement and the permanent record produced which with the record direction will befinder free illustrated of any bearing in Fig. on the chart »it will show a null of zero or minimum signal inten 'ty in each quadrant of hiffuity, it is necessary only to throw the switch each 350° record. Substantially entirely vertin 32 to its right-hand position for one or more cally polarized waves will be supplied to the an revolutions of the antenna arrangement, whereby tenna arrangement. however, only when a plane a cardicid pattern, having only zero or m is leaving the airport where the antenna arrange mum intensity position, will he produced on the i‘cd. At distance of approximately to chart .its lett-hand ¿8, and thereafter position soto asthrow to produce, the switch during 60 miles. utilizing medium high frequencies of the character heretofore indicated which may vary succeeding revolutions of the antenna arrroigen from 1.5 to 30 megacycles. it will be found that in 25 ment, a continuous trace of the signal intensity addition to the vertically polarized ground Wave of the character hereinbefore i- dicated. there will be received at the antenna arrange The cardioid pattern itself cannot he used for ment horizontally polarized s’sy waves propagated determining the true bearing of the transmitter by the ione-sphere, and t. at a distano.. of approxi station, due to the polarization errors and the mately 206 miles the ground wave will substan 30 like which may cause a variation in the null of tially disappear. the cardioid of such great magnitude as to render The horizontally polarized sky waves will of the cardioid pattern useless from the bearing course induce in each or" the loop antennas a voltage which cannot be eliminated merely by standpoint. The cardioid pattern will, however, indicate in'what quadrant a plane or transmi Ling rotating one of the antennas, but, as in the case 35 station is located, and the quadrant having thus of a vertically polarized ground wave, the voltages been determined, the true bearing may readily be induced in the two loop antennas, when the beam ascertained from the continuous records produced i 2 occupies a position substantially at right angles with two loop antennas connected in parallel to the direction of the transmitting station, will opposed rela-tion as described above. cancel out, due to the fact that the two loops are 40 In Fig. 6 there is shown a typical trace 68 on a connected in opposed parallel relation and that linear chart constituting a portion of the chart in this position there will no diversity error. lit, which trace $8 represents a true bearing havm In all other positions of the antenna arrange-v ing a readily discernible null or minimum Ei* ment a diversity error'occurs due t0 the differ which represents the true bearing of the plane ence in time phase of the incoming waves with 45 or transmitter. By referring the point 69 to one respect to the two spaced loops. ofthe reference marks 5S by the tracing From the above it will be clear that as the element 5‘! on the chart 48, the correct bearing antenna arrangement is rotated at a constant of the transmitting station may readily be noted. speed, there will be prodi'> .d on the chart 48 a In Figs. 7 and 8, representative ink traces are continuous record wh' h t. .l show either two or 50 shown which indicate false bearings, the ink trace four positions of m .icio l or zero signal in tensity during each revo ‘on of the antenna ’lo in Fig, 7 having a series of points li, l2, and 'i3 whichl might easily have been mistaken for a arrangement, depending noon the character of true bearing if headphones had been used in the the incoming wave, and accordingly there will be customary manner connected to the output of the an ambiguity in the record since obviously only 55 receiver 29. ,. one of these positions of minimum signal in unskilled It is a relatively operator simple that amatter trace having to teachthe even gen tensity indicates the true bearing of the plane or transmitter station. eral conñguration shown in Fig. 6 and only that It is for the purpose of overcoming this bear trace represents an accurate bearing. According ing ambiguity that the vertical antenna te and 60 ly, by mere inspection the operator can discard its associated connections are provided, the verti traces such as are shown in Fig. 7 from any single cal antenna being connected as shown by a trans~ group, and thus eliminate all of those bearings mission line 59 to a slip ring @t carried by the which are obviously false. erroneous trace rotating post i3, and a brush El, which is ar illustrated in Fig. '7 may of course be due to fading ranged to contact the slip ring Sii, connects the 65 and to deviation errors caused by minute-by vertical antenna through conductor 62 to the minute variations in the ionosphere. Prefer movable blade @3 of the switch 32. When the ably, the antenna arrangement is rotated at the switch 32 is in its left»l'iand position, as pre rate of approximately i5 revolutions per minute. viously described so as to connect the loop an~ and by thus taking a relatively large number of tennas l0 and l! in opposed parallel relation, the 70 traces during a short period it is possible to ob vertical antenna I4 is open circuited and the continuous record or trace heretofore described is obtained. When, however. the switch 32 is thrown to a right-hand position, the loop antenna Il is cut out of circuit and a suitable artificial 75 tain one or more true bearings when fading is nonexistent, even though over the general period severe fading conditions may exist. In Fig, 8 there is shown a chart having an inl; trace 'I4 thereon which is identical with the ink 2,406,406 7 trace 10.0f Fig. '7, and superimposed on the trace 14 there is indicated in broken lines a trace 15 which would have been formed if no fading had ~ which the band-pass ñlter 39 is designed to pass. For example, if the band-pass ñlter ís designed t0 pass a frequency of 1020 cycles plus or minus 30, the frequencies of the crystal oscillators will be so selected as to have a frequency difference equal to been present. While movements or changes in the ionosphere during the time that a bearing is being recorded are indicated by irregularity in the trace 5|, a true bearing may be located by compar- ' ing the portion of the false trace adjacent to the apparent minimum with a standard trace of a true bearing. Thus, if a trace corresponding to a true bearing is printed or otherwise made on a trans parent card, formed for example of Plexiglas or other similar material, such a standard bearing may be superimposed on a bearing trace such as the bearing trace in Fig, 8, and it will immediately 15 become apparent that the trace 14 represents a false bearing and may be discarded. Thus it is possible by comparison with a standard trace to eliminate the element of judgment, and even un skilled operators may readily discard all improper 20 bearings and determine immediately those traces which represent true bearing readings. In order to assure the accuracy of the bearings obtained, the loops Il! and I l, and hence the drum »11.9, may be allowed to rotate a number of times 25 (at least l5) for each bearing desired. In this manner a number of bearings are superimposed one over the other and can be readily averaged to secure a resultant bearing more accurate than any individual bearing. , 30 1020 cycles. When the frequencies of the two crystal oscillators and the carrier are impressed on the control electrodes of the converter tube 16, two beat frequencies will be generated equal re spectively to the difference between the carrier frequency and the frequency of oscillator 80, and to the >difference between the carrier frequency and the frequency of oscillator 8l, and these two beat frequencies pass from the converter tube 16 to the I. F. amplifier indicated diagrammatically by the reference numeral 82. From the I. F, am pliñer these frequencies pass to the detector and audio stage indicated diagrammatically and iden tified by the reference character 83, and beat to gether at the detector to form a beat note equal to the difference between the two intermediate fre quencies. It will be found, upon analysis, that the frequency transmitted to the band-pass filter will always be equal to 1020 cycles, i. e., the differ ence between the frequencies of the two crystal oscillators, regardless of the carrier frequency of the transmitter, and accordingly the entire band will be successfully passed by the band-pass filter 39. By thus insuring that the entire useful fre quency band transmitted to the band-pass filter 39 will be within the range of the filter, and by As heretofore mentioned, various errors may be very sharply tuning the band-pass filter, the introduced into the continuous records or traces effects of static may be very substantially min obtained with the direction finder system illus imized or entire eliminated, and accordingly more trated in Fig. l, due to the presence of static con ditions, and in order to eliminate or minimize the 35 accurate bearing traces will be obtained on the chart 48 ofFig.l. ‘ 1 ‘ ' effects of static the band-pass filter 39 is inter In the direction finder system illustrated in posed in the output circuit of the radio receiver, Fig. 1, a manual switch 32 is shown for control as shown in Fig. 1, which band-pass filter is very ling the antenna connections so to 'produce sharply tuned so as to pass only a very narrow band of frequencies. As is the usual practice in 40 a cardioid pattern when desired, in order to re move the ambiguity from the true bearing rec radio direction finders used today for determining the position of airplanes on commercial airline ords obtained on the chart 48, but it has been found desirable to provide automatic means for systems, the receiver 29 of the direction finder controlling the antenna connections in order to ` system shownl in Fig. 1 is capable of receiving only stations transmitting-a carrier frequency having a 45 produce the cardioid, and in Fig. 3 there is shown means for automatically exercising a proper con fixed relation to the fixed frequency of oscillator trol of the antenna connections. Y 31, and the band-pass ñlter is tuned to pass only « In Fig. 3 the coupling means for the antennas the beat note frequency resulting from the re is illustrated as an electromagnetic relay or ceived carrier and the frequency of the oscil lator 31; ' It has been found, however, that the frequency of the transmitting station, although intended to be a fixed value, will vary over such a wide range that the beat note frequency supplied to the band pass filter may vary as much as '750 cycles. Varia switch having an operating winding 85 and a movable magnetizable core or armature 85 ar ranged to operate a plurality of contacts 33, 34, and 63, which respectively correspond to the sim ilarly numbered knife blades of the manual switch 32 in Fig. 1. This electromagnetic relay, which may be termed the cardioid relay, is like Wise provided with the stationary contacts 39 and 3l which correspond to the similarly num beredcontacts of the switch 32, and which are culty the arrangement illustrated in Fig. 2 is pro 60 normally engaged by the movable contacts 33 and vided. 34 for connecting the loop antenna H in paral In Fig_ 2 the receiver 29, which receives the car lel relation with the loop antenna lil through rier frequency from the antenna arrangement K the conductors 35, 26, 21, and 2B, as described through the conductors 21 and 28, is shown some what diagrammatically as including a converter in connection with Fig. 1. When the winding B5 of the cardioid relay is tube 16 having a plurality of control electrodes 11, energized, the circuit of the loop antenna Il is 18, and 19, the control electrode 19 being supplied with the carrier frequency through the radio fre interrupted at the contacts 33 and 34 and the quency stage (not shown) of the receiver 29, and ' artificial antenna 54a is connected in parallel the control electrodes 11 and 18 being respectively with the loop antenna iii through an upper pair connected, as shown, to separate crystal oscil 70 of contacts engaged by the movable contacts 33 and 34. At the same time, the movable contact lators 80 and 3| which correspond to the oscil 63 of the cardioid relay closes a circuit similar lator means 31‘of Fig. 1. The two crystal oscil to that hereinbefore described in connection with lators 8i! and 8| are arranged to produce fixed Fig.. 1, whereby the vertical antenna ill isvcon frequencies, there being a frequency difference loe tween the'two oscillators equal to the frequency 75 nected through the conductor 62, the contact 63, tions of this magnitude would of course mean that certain of these frequencies would not pass the filter S9, and in order to overcome this diffi 2,406,406 9 10 the stationary contact 64 and a conductor @aand condenser II8 to the ground connection |22. by way of the phase shifter Së- to the receiver 23. It will thus be apparent that the cardioid relay, when alternately energized and deenergized, ef The energizing circuit for the relay iël2 estab lished by closure of the contacts Ill' may be traced 4from one side of the condenser IES, through the conductor |22, the contacts Ill, the fects the Same circuit connections as are effect ed by throwing the manual 'switch 32 from one of its positions to the other. In order properly to control the operation of conductor |23, the winding |2I of the relay |82, conductor |25, the contacts QQ 'on relay 88, which as previously described has been operated by clo the cardioid relay, a rotatable lSwitch 3l is pre-_ vided, which is preferably associated with the 10 rotating post i3 of the antenna arrangement, and arranged to complete a circuit once during each revolution ci post i3. Closure of the switch El completes an energizing circuit for a control relay 83 having an energizing winding 15 89, two pairs of normally open contacts ëü and löta, respectively, and a pair cf ,'oorrrially` closed contacts 9i. circuit may be traced from sure of the switch means 8l, and by way of the conductor 29 and the ground _connections ‘|253 and I 2d tothe other side ‘of the condenser I I8. Following> initial energization thereof, the 1' - lay m2 is held in its operated position by a hold ing circuit which maybe traced from the posi tive termina1 92, through the conductors 93, Sá, 95, and |36, contacts ISSUL, conductor Kila, con tacts |38a, conductor |3911, the winding |2IY of the relay Iû2, conductor í2fì, contacts 39, and by the positive side of a »suitable source of energy way of the conductor Sil to the ground connec indicated by the reference numeral Si?, through the conductors Q5, Q6, and e?, the switch 8l, the conductor the relay winding £9, and tion Iilt‘. by lway of a conductor to to the `negative side of the source of energy or a ground connection, indicated by the reference numeral lili), Associated with the control relay $3, and the rotating switch means Eil are a plurality of ad ditionalcontrol relays 252i, to2, and the en ergizing winding Iilél of the relay ¿53 being c 'i nected in the output circuit of a full re - ` Closure of the contacts |25 of the‘relay |02 establishes an energizing, circuitV for the winding l|29 of the relay lill; which circuit may be traced from the positive terminal 92 through conductors 93, 94, and |26, contactsjlZö, conductors |21 ‘and |28, and by way of the winding I 29 tothe ground connection |30. The relay IUI is thus operated and the energizing circuits thus far traced con tinue to exist until the circuit is broken at the contacts of the switch means 8'l,'at which time the relay 8S is deenergized, allowing contacts ISSa pair ñer £25 of cathodes having a ill?, pair and of plates a pairorofanodes controlloll, ele and Sû to open and contacts 9| to close.A Opening 0f the contacts |36a‘ interrupts, the previously traced holding circuit for the relay |52, and the ments or grids H98. As shown, the grids or ccn trol elements lûâ are adapted to be energized from a secondary winding log of a suitable cou ‘ consequent opening of 'the contacts |25 on the pling transformer, the primary winding ¿Iii of relay |ü2 in‘ turn interrupts the energizing circuit for the relay ItìI. Simultaneously, however, clo which is connected to a suitable antenna for eu ergization by the carrier of the transmitting sta tion to which the radio direction under systea-„i preferably of Fig. lisconnected tuned. YThe to _the primary systemwinding of lliï; at a sure of the contacts 9| on'the relay 88 provides a self-holding circuit for the relay lill, which may be traced from the positive terminal 92 through the conductors 93," 94, S5, and |36,A contacts 9|, conductor |37, contacts I S2, ’conductors |38 and or` point it may, between if desired, the filter be connected E@ and theto rectifier an entirely separate antenna and receiver. En order to pro |28, and by way of the winding 'I 29 tothe ground connection |36. This transfer of the holding cir cuit for the relay EOI is accomplished without vide a constantnegative bias on the control ele ments iílß or the rectifier tube itâ, the midpoint aîîecting the operated condition'of the relay, be `of ground the secondary as shown and winding the cathodes lol?, is connected iol are con nected to a suitable potentiometer represented as cause this relay is of the slow-to-release type as indicated 'diagrammatically in'Fig. 3 by the usual copper'slug` COmIJYîSing the resistanceelements l il connect 50 |39.` , ' ' ' ’ Operationuof the` relay IDI of course causes ed across the direct current source of energy rep closure of the relay contacts I 3|, thereby coin resented bythe positive terminal 92 and the pleting an energizing circuit for the cardioid re ground connection I l2. lay which may be traced from the positive source Whenever carrier energy is being supplied to of energy`92 through the conductors 93, 9&3, 95, 96, the rectifier tube throughthetransformer, cur 55 and I33,_the`contacts I3‘I, the conductor |34, and rent will flow through the winding `lofi of the by way of the operating winding 650i the cardioid control relay Illâ through a circuit which er; relay to the ground connectionf'lää. Upon eher tends from the 'positive `source of energy 22 gization of this operating winding 85, the arma through theconductors 93 and IIS, the Winding ture 8E `V>of the cardioid'relay is operated to its |04, the conductor ll-fl, the anodes lot, the cath 60 uppermost ‘posi'tion‘so' 'asfto >connect the'vertical odes IIl'I, and by way of the conductor H5 to the antenna kin circuit th'rou'gh‘the contacts B3 and movable contact H3 on the potentiometer iii. 64, as heretofore described, During the’ensuing In describing the operation of the automatic revolution- of the' antenna; means a cardioid pat control means it ywill be assumed that power has tern is produced on ~the chart 48 of Fig. l. j been applied to the operating mote-rs of the an 65 tenna arrangement, thereby operating ‘the Iswitcl'l means 8l, and that a carrier is being supplied to the 'winding H8 of the transformer ‘so as to ef This connection exists until the contacts :of the switch means 8T, are againfclosed after one com plete revolution rof the‘rotatable’post` I3, where upon the relay` 8B will again be `energized through fect operation of the relay lili. Upon closure of the previously traced energizingcircuit causing the contacts H'i' of the relay I?ë, a condenser 70 the contactsol to open and interrupt the pre ||8 will effect energization of the relay 532, the viously traced self-holding` circuit‘for `the relay condenser having previously been charged |0|. The capacity of the condenser H8 and the through a` circuit which may be traced from the ohmic resistance of the resistor I I9 areso chosen positive terminal 82, through the conductors 93 and H3, theV resistor H9, conductor |22, and the that during successive closures Aof the contacts 1,5 of the switch 'means 8_1“ there will elapse an in afìoefioe . 11 suiiîcient time to permit the accumulation on the condenser I I8 of a charge of suiiicient magnitude to eiiect operation of the relay |02." Therefore, even though the initial energizing circuit for the relay |02 is completed through the contacts 90 of the relay 98 when this relay is again operated, 12 _ mined relation to the carrier frequency received from the two antennas, and accordingly beats therewith to generate identical intermediate fre quencies. The coupling transformer |46 to which the intermediate frequency from the vertical an tenna is supplied, is connected as shown through the conductors |59, the phase shifting device 66 the relay |92 will not operate, and accordingly the and the conductors |5| to the conductors |52 relay |9I opens, thereby interrupting at contacts which lead from the coupling transformer |42 of |3| the energizing circuit for the cardioid relay. the vertical antenna to the intermediate fre Thus the cardioid relay returns to the position 10 quency amplifier and detector |49. ' shown in the drawings, and the antenna circuits Thus, the adjustment of the phase shifter 66, are connected with the parallel opposed loops in for effecting the desired phase shift in the energy circuitV as heretofore described. Due to the fact received from the vertical antenne, I4 with re that> theecapacity and >resistance values of the spect to the energy received through the loop 15 condenser H9 and the resistor ||9, respectively, antenna IIì, is a function of the intermediate fre are‘chosen as indicated above, the operating cycle quency only and will accomplish the proper phase cannot be nrepeated unti1 sufficient time has shifting regardless of the frequency to which the elapsed-to permit the condenser IIB to attain a two antennas are tuned. From the I. F. ampli new charge of sufficient magnitudeV to operate the ñer and detector |43 the combined energy from 20 relay |92. ’ ` " the two antennas is supplied through suitable However, after the desired record has been conductors to the rectifier and the recording made from which a true bearing may be located and the system has been allowed to rest for a relatively short time, operating voltage will build means of Fig. 1 so as to trace on the chart 48 an accurate cardioid pattern of the combined energy received. ` upV across the condenser ||8 and the above de In Fig. 5 there is shown a still further modified scribed cycle of ' operations may be repeated. circuit arrangement which may be employed Such an operating voltage will not build up across when it is desirable to prevent overloading the the condenser |I8 until the system is allowed to radio direction finder system shown in Fig. 1 reist because of the'fact that the’ condenser is dis without interfering with .the accuracy of the var charged each time the contacts 99 of the relay 88 30 iations of signal intensity received as a function close, the discharge howevef being insuñicient to of the position of the loop antennas.> It will, of effect operation of the relay |92. In the pre course, be clear that, if the usual automatic vol ferred arrangement, control of the automatic ume control is employed on the receiver 2'9Iof cardioid control means illustrated in Fig. 3 may be accomplished by providing a manually oper 35 Fig. 1, this control will tend to maintain con ated control button or switch which serves simul'-~ taneously to connect the source of energy to the circuit of Fig. 3 and to the operating motors I5 stant the output of the receiver and thus will destroy the sharpness of the nulls used to deterL mi-ne the true bearing ofV the transmitter. In Fig. 5, however, an automatic volume control ar and 50 of the radio >direction finder system shown in Fig. 1, and it will be observed that when the 40 rangement is shown which is not detrimental to the accuracy of the direction finder: AS illus energy source is thus connected, the above cycle trated in Fig. 5, the loop antenna I9 is connected Y of operations will automatically be carried out to a radio receiver which correspondsto the re whenever a suitable carrier is‘applied to the pri ceiver 29 of Fig. 1 and is shown as including mary winding' | l0.’ ' anV R. F. stage, a first detector, and two I. F. In Fig. 4 a somewhat modiiied arrangement of amplifiers having the control elements of each the circuits is shown which may be employed in tube connected together in the conventional man the radio direction finder system of Fig. l in order ner through suitable resistors |53, |54, |55, and to insure that the radio frequency energy received |56. The output from the receiver 29 may vbe in the loop antenna I0 and the vertical antenna connected through a suitable rectifier correspond I4, when these two antennas are connected to ing to the rectifier 49 of Fig. 1 to recording means gether for the production vof a cardioid pattern, for producing a trace of the signal intensity re be' shifted to the proper phase relation for pro ceived by the antenna I9. , duction of a cardioid pattern at al1 times, even The vertical antenna I4 in this arrangement, though the tuning of the antennas be variable so however, is connected to a separate receiver in- Y as to receive the carrier frequencies of transmit dicated diagrammatically and identified by the ters operating on different radio frequencies. In reference numeral |51, which may be entirely the circuit shown in Fig. 4, the radio receiver 29 conventional and which includes a detector |58 is represented diagrammatically as including a having a suitable resistance |59 connected in its radio frequency stage having a tuning trans former |40 and a converter tube I4| connected 60 output circuit. The rectified output of thevde tector |58 is, of course, a function of the signal by a converter transformer |42 to the interme intensity received on the vertical antenna and diate amplifier and detector indicated diagramf this rectiñed output is impressed by meansof matically by the reference numeral |43. The ver the conductor |69 on the gain control or grid tical antenna I4, instead of being connected di~ rectly to the phase shifter 56 of Fig. 1, is con 65 circuits of the various elements of the directional nected to a receiving means comprising a radio frequency stage identical with the radio fre quency stage of the receiver 29 and comprising a tuning transformer |44, a'converter tube |45, anda coupling transformer |46. . receiver 29. . While the output of the receiver 29 supplied to the rectifier and recording means is a function of the position of the loop antenna I9 and the 70 direction of the transmitter, this output will be substantially independent of variations in the carrier intensity due to the» automatic volume control exercised by the> connection to-thede' tector output of the vertical antenna receiver frequency oscillator |49. The radio frequency supplied by the oscillator |49 bears a predeter-l 75 |51, and accordingly‘overloading and errors .'due The converter tubes |4I and |45 are provided Y with control grids |41 and |48, respectively, which control grids are' connected to a suitable radio 13 :2,406,406 to fading are minimized or prevented. It will of course, be understood that use of the separate receiver l5? is in addition to, rather than in place of, the circuit connections for the vertical an tenne, shown in Figs. 1 and 4, the receiver |51 being separately coupled to the vertical antenna le or being energized from an entirely separate vertical antenna if desired. As previously described and as shown in Fig. 1, the preferred directional antenna means oom prises the loops I@ and H mounted on opposite ends of the horizontally extending beam l2 which is supported at its midpoint on the rotatable post i3. While the detailed mechanical structure of thebeam nI2 .forms no part of this invention, it is important that the beam be suil‘lciently strong and rigid to withstand any tendency of the loops to twist relative to each other, as any such twist ing would introduce diversity errors into the bear ing readings. Although the loops may be secured to the beam i2 in any desired relation thereto, they are pref erably supported thereon at their lower edges, selectively operable to one of two positions to couple one of said loop antennas and said non directional antenna to said receiver in parallel relation and to the other of said two positions to couple said pair of loop antennas to said receiver in opposed parallel relation, relay means respon sive to rotation of said antenna means for auto matically operating said coupling means between said two positions, and recording means energiz 10 able in accordance with the output energy of said receiver for producing a lasting visual record of the signal intensities supplied to said receiver during rotation of said antenna means with said coupling means in either of said two positions. 15 3. A radior direction finder comprising a re ceiver, directional antenna means including a pair ci" loop antennas ?ixedly mounted with respect to each other in spaced substantially coaxial rela tion, means for rotating said antenna means at 20 a substantially constant speed about an axis sub stantially parallel to the planes of said loops, a non-directional antenna, coupling means selec tively operable to one of two positions to couple as shown, and the beam l2 may act as a horizon one of said loop antennas and said non-direc tal antenna. Consequently it may be desirable, 25 tional antenna to said receiver in parallel relation in order to minimize any coupling between the and to the other of said two positions to couple beam and the loops, to support the loops with a pair of loop antennas to said receiv r in slight inclination from a true right angular ver opposed parallel relation, and relay means con tical relation to ythe beam, although maintain trolled by rotation of said antenna means for ing, of course, the substantially coaxial relation 30 initially operating said coupling means to said of the loops. The respective dimensions of the one position and for thereafter operating said loops l@ and Il and the spacing therebetween of coupling means to said other position upon com course depends to a large extent upon the fre pletion of a predetermined rotation of said an quencies employed, the spacing of the loops being tenna means. less than one-half wave length, and the entire 35 e. A radio direction ñnder comprising a re antenna structure, as heretofore stated, is ro pair c ’ er, of directional loop antennas antenna fixedlymeans mounted including with re tated at a constant speed which may preferably be on the order of 15 R. P. M. spect to each other in spaced substantially co While particular embodiments of the invention axial relation, means for rotating said antenna have been shown, it will, of course, be under 40 means at e, substantially constant speed about an stood that the invention is not limited thereto, axis substantially parallel to the planes of said since modiñcations may be made, and it is there loops, a non-directional antenna, coupling means fore contemplated by the appended claims to selectively operable to one of two positions to cover any such modifications as fall within the couple one of said loop antennas and said non 45 directional antenna to said receiver in parallel true spirit and scope of the invention. Having thus described our invention, what we relation and to the other of said two positions to claim and desire -to secure by Letters Patent is: couple said pair oi’ loop antennas to said receiver 1. A radio direction ñnder comprising a re in opposed parallel relation, recording means en 'crgizable in accordance with the output energy ceiver, directional antenna means including a pair of loop antennas iixedly mounted with re 50 of said receiver for producing a lasting visual spect to each other in spaced substantially oo record of the signal intensities supplied to said receiver during rotation of said antenna means axial relation, means for rotating said antenna means at a substantially constant speed about with said coupling means in either of ,said two an axis substantially parallel to the planes of said positions, and relay means controlled by rotation of said antenna means for initially operating said loops, a non-directional antenna, coupling means coupling means to said one position to produce selectively operable to one of two positions to a cardioid pattern on said recording meansy and couple one of said loop antennas and said non for operating said coupling means to said other directional antenna to said receiver in parallel position after completion of said oardioid pattern relation and to the other of said two positions to couple said pair of loop antennas to said re 60 to record the signal intensity supplied to said receiver during subsequent rotations of said op ceiver in opposed parallel relation, and recording posed loops. means energizable in accordance with the output 5. In a radio direction ñnder having directional energy of said receiver for producing a lasting antenna means including a plurality of antennas visual record of the signal intensities supplied to said receiver during rotation of said antenna 65 adapted to be selectively coupled together in pre means with said coupling means in either of said determined dil'lîerent circuit relations, and a ro tating part the compass position of which is re rlected in the signal intensity output of said an 2. A radio direction finder comprising a re tenrla means, the combination of coupling means ceiver, directional antenna means including a pair of loop antennas ñxedly mounted with re 70 operable between two positions to vary the said circuit relations of said antennas, a source of spect to each other in spaced substantially co energ‘ , means connected to said source for stor axial relation7 means for rotating said antenna ing a charge of energy during idle periods of said means at a substantially constant speed about an `axis substantially parallel to the planes of said direction ñnder, means jointly responsive to rota loops, a non-directional antenna, coupling means 75 tion of said antenna part and to a carrier received two positions. 2,406,406 'l5 by said antenna means for discharging said stored 16 ceiver, directional antenna means coupled to said` receiver and having a rotatable part the com energy to operate said coupling means to one of pass position of which is reflected in the signal said positions, means effective upon completion intensity received from said antenna means, re of a predetermined rotation of said part for op erating said coupling means to the other of said U1 cording means including a pair of relatively movable parts respectively comprising a record~ positions, and means for preventing recharging ing surface and a co-operating tracing element, ci’ said energy storing means during further rota means for rotating said rotatable-part of said an tion of said antenna part. 6. A radio direction finder comprising a re tenna means at a constant speed, means for mov of loop antennas fixedly mounted with respect to each other in spaced apart relation, means for rotating said antenna meansat a substantially constant speed abo-utV a substantially vertical medial axis, a non-directional antenna, coupling means selectively operable to one of two positions to couple one of said loop antennas and said non directional antenna to said receiver in parallel relation and to the other of said two positions to couple said pair of loop antennas to said receiver in opposed parallel relation, and recording means energizable in accordance with the output energy synchronism with said antenna part, means for moving the other of said parts of said recording means in accordance with the output of said ceiver, directional antenna means including a pair 10 ing one of said parts of said recording means in of said receiver for producing a lasting visual receiver to form on said recording surface a con tinuous record of the signal intensity received from said antenna means, means controlled by the rotation of said rotatable antenna part for automatically orienting said continuous record with respect to the compass position of said an tenna part, and means for comparing said con tinuous record with a standard record to produce an evaluation of the compass >bearing quality. 10. A radio ldirection ñnder comprising a re ceiver, directional antenna means coupled to said receiver during rotation of said antenna means 25 receiver and- having a rotatable part the com pass position of which is reflected in the signal with said coupling means in either of said two intensity of ’said antenna means, recording means positions. . including a pair of relatively movable parts re ’7. A radio direction finder comprising a re spectively comprising a recording surface and a ceiver, directional antenna means including a pair 0I" loop antennas iixedly mounted with re 30 co-operating tracing element, means for rotating said rotatable part of said antenna means at a spect to each other in spaced apart relation, record of the signal intensities supplied to said means for rotating said antenna means at a sub constant speed, means for rotating one of s-aid parts of said recording means in synchronism stantially constant speed about a substantially with said antenna part, means controlled by the vertical medial axis, a non-directional antenna, coupling means selectively operable to one of two 35 rotation ofV said rotatable antenna part for auto m-atically recording on said surface a reference positions to couple one of said loop antennas and position or“ said antenna part, means for moving said non-directional antenna to said .receiver in the other of said parts of ~s_aid recording means parallel relation and to the other of said two posi in accordance with the output of said receiver tions to couple said pair of loop antennas to said receiver in opposed parallel relation, recording 40 to form~ on said recording surface during each revolution of said one part and said antenna part means energizable in accordance with the output a continuous record of the signal intensity re energy of said receiver for producing a lasting ceived from said antenna means, the continuous visual record of the signal intensities supplied to records formed during succes-sive revolutions be said receiver during rotation of said antenna means with said coupling means in either of said 45 ing superimposed on said'recording surface to provide a resultant average of said signal inten two positions, and means for comparing with a sity, and comparative means comprising a trans standard bearing record the continuous visual parent element having a standard bearing trace record produced during said opposed parallel thereon for determining by comparison with connection of said loops to evaluate by inspection the co-rnpass bearing quality of said continuous 50. each of said records the quality of the compass bearing indicated thereby. record. 11. The method of determining the bearing 8. A radio direction finder comprising a re quality characteristics of portions of a continu ceiver, directional antenna means coupled to said ously recorded trace of the signal intensity re receiver and having a rotatable part the com pass position of which is reiiected in the signal 55 ceivedY by a radio direction iinder receiver, which comprises preparing on a transparent medium a intensity received fro-m said antenna means, re cording means including a pair or relatively movable parts respectively comprising a record standard bearing trace corresponding to a true bearing trace for the said receiver, superimposing said transparent medium on the continuous rec ing surface and a coi-operating tracing element, means for rotating said rotatable part of said 60 ord of said signal intensity, and causing portions vof said standard bearing trace to coincide with antenna means at a constant speed, means for portions of said signal intensity trace visually toY moving one of said parts of said recording means establish the character of variations from said in synchronism with said antenna part, means standard’bearing trace in other por-tions of said for periodically recording on said surface a ref erence position of said antenna part, means for 65 signal intensity trace. l2. In a radio direction finder having direc moving the other of said parts of said recording tional antenna means including a plurality of means in accor-dance with `the output of said re antennas adapted to be selectively coupled to ceiver- to form on said recording surface a con gether in predetermined diiïerent circuit rela tinuous record of the signal intensity received from said antenna means, and means for deter 70 tions and a rotating part the compass position of which is renected in the signal intensity output mining from said continuous record of signal in of said antenna means, the combination of cou tensity the behavior of the radio wave propagat pling means operable between two positions to ing medium during the time of operation of said vary the said circuit relations of said antennas, radio direction finder, 9. A radio direction ñnder comprising a re 75 means for operating 'said coupling means, relay 2,406,406 17 means for selectively energizing said operating means to operate said coupling means between said two positions, and interlock means for ren dering said relay means effective to energize said operating means only when a carrier is being received by said antenna means. 13. In a radio direction ñnder having direc tional antenna means including a plurality of 18 one 0f said parts in synchronism with the rota tion of said antenna means, and means for mov ing the other of said parts in accordance with the output of said receiver means to form on said recording surface a continuous record of the signal intensity received from said spaced loops. 16. A radio direction finder responsive to fre quencies in the range wherein bearing deter minations are affected by the characteristics of antennas adapted to be selectively coupled to gether in predetermined different circuit rela the ionosphere, comprising directional antenna tions and a constant speed rotating part the com means including a pair of loops ñxedly mounted pass position of which is reiiected in the signal with respect to each other in spaced substantially intensity output of said antenna means, the com coaxial relation, means for rotating said antenna bination of coupling means operable between two means at a substantially constant speed about positions to Vary the said circuit relations of said 15 substantially the vertical axis of symmetry of antennas, relay means controlled by rotation of said spaced loops, receiver means adapted to pro said antenna part for selectively operating said duce in the output circuit thereof a signal inten coupling means between said two positions, and sity continuously proportional to the signal in interlock means for rendering said relay means tensity supplied to the input circuit thereof, effective to operate said coupling means only 20 means coupling said receiver means to said an when a carrier is being received by said antenna tenna means whereby the compass position of means. said loops is reflected in the signal intensity sup 14. In a radio direction finder having direc plied to said receiver means, recording means tional antenna means including a plurality of including a pair of relatively movable parts re antennas adapted to be selectively coupled to spectively comprising a recording surface and a gether in predetermined different circuit rela co-operating tracing element, means for moving tions and a constant speed rotating part the one of said parts in synchronism with the rota compass position of which is reñected in the tion of said antenna means, means for moving signal intensity output of said antenna means, the other of said parts in accordance with the the combination of coupling means operable be 30 output of said receiver means to form on said tween two positions to vary the said circuit rela recording surface a continuous record of the tions of said antennas, relay means controlled signal intensity received from said spaced loops, by rotation of said antenna part for selectively and means for periodically recording on said operating said coupling means between said two surface a reference position of said loops relative positions, said relay means including interlock 35 to said continuous record. means responsive to a carrier received by said 17. A radio direction ñnder responsive to fre antenna means for preventing operation of said quencies in the range wherein bearing deter coupling means when a carrier is not being re minations are affected by the characteristics of ceived by said antenna means. the ionosphere, comprising directional antenna l5. A radio direction finder responsive to fre 40 means including a pair of loops fiXedly mounted quencies in the range wherein bearing deter with respect to each other in spaced substantially minations are affected by the characteristics of coaxial relation, means for rotating said antenna the ionosphere, comprising directional antenna means at a substantially constant speed about means including a pair of loops ñxedly mounted substantially the vertical axis of symmetry of with respect to each other in spaced substan said spaced loops, receiver means adapted to pro tially coaxial relation, means for rotating said duce in the output circuit thereof a signal inten antenna means at a substantially constant speed sity continuously proportional to the signal in about substantially the vertical axis of symmetry tensity supplied to the input circuit thereof, of said spaced loops, receiver means adapted to means coupling said receiver means to said an produce in the output circuit thereof a signal 50 tenna means whereby the instantaneous compass intensity continuously proportional to the signal positions of said loops during rotation are re intensity supplied to the input circuit thereof, flected in the instantaneous signal intensities means coupling said receiver means to said an supplied to said receiver, and recording means tenna means whereby the compass position of energizable in accordance with the output of said said loops is reflected in the signal intensity sup 55 receiver means for producing a lasting record plied to said receiver means, recording means trace proportional at all points to the signal including a pair of relatively movable parts re intensities received from said spaced loops. spectively comprising a recording surface and a PETER C. SANDRETTO. co-operating tracing element, means for moving ELMER P. BUCKTHAL.