Патент USA US2403603код для вставки
July 9, 1946. 2,403,603 A. KORN WIRELESS COMMUNICATION Filed Feb. 5, 1941 I 13 ‘0 5 Sheets-Sheet l I6 lo' / 5| PLANE I |3000 FEET ALTITUDE |2500 FEET PLANE 2 Aurrrups FIC-3.2¢ ARTHUR KORN July 9, 1946. A. KORN 2,403,603 WIRELESS COMMUNICATION Filed Feb. 5, 1941 Ow mw 5 Sheets-Sheetv 2 mOFUJm»alma am.. «2u.530. m„no. . INVENTOR ARTHUR KORN AL, ATTORNEY` July 9, 1946. A. KORN 2,403,603 WIRELESS COMMUNICATION Filed Feb. 5,i 1941 5 Sheets-Sheet 3 IlrLI. ON IKNvENToà _ ARTHUR KORN m5 l 16am/la. al@ ATrQRNEY July 9, 1946. A. KORN 2,403,603 ` WIRELESS COMMUNICATION Filed Febfä, 1941 5 'sheets-sheet 4 - INVENTOR. BY MMM/Km» July 9, 1946. 2,403,603 A. KORN WIRELESS COMMUNICATION Filed Feb. 5, 1941 5 Sheets-Shèei’l 5 ~ -OFUmJwTl I <„1l| _l I N p'î - mvENToR ARTHUR KORN L.. BY Qx l ‘l »QM aMATroRm-:v A , Patented July 9, 1946 _ 2,403,603 1 PATENT' oFFlci;- UNITED STATES 2,403,603 WIRELESS COMUNICATION Arthur Korn, Hoboken, N. J., assignor to Square D Company, Detroit, Mich., a corporation _of Michigan Application February 5, 1941, Serial No. 377,516 21 claims. l 2 This invention relates to a method of, and ap paratus for, wireless communication, more par “ticular1y.designed for communication with and between aircraft. . matically scanning a. band of carrier frequen cies in dependence on the altitude of the receiv ing craft and indicating the presence of other craft in the proximity by indicating their rela ~ It is an object of this invention to provide a 6 tive alütude with respect to the receiving craft method of, and an apparatus for, wireless com and, in further development of this invention, in munication permitting an airplane -in'fiight to addition, the direction of ñight of such craft.A More specifically, the invention aims at Dro communicate to other planes or a station on the ground Within a predetermined range or dis tance certain Hight data as, for example, its alti tude and its direction of flight. „viding a combined transmitter and receiver for ~ ‘ l0 the continuous transmission of signals represent ing altitude of a transmitting craft and simul taneously scanning a band of carrier frequen It is thus a purpose of the invention to com municate to the pilot of a plane in flight cer cies in dependence on the altitude level of the tain flight information such as altitude or direc transmitting craft including means for protect- ' tion of flight, or both, of other craft in the vicinity 15 ing the receiver from signals of the transmitter of the plane in order to eleminate the danger of with which it is combined. The invention further aims at improving the or poor visibility. above method of, and apparatus for, communi It is a further purpose of this invention to Pro.. cation by providing steps and means for elimi vide a method of, and means for, communica 20 natinginterference by stray signals. tion between an airport operator and planes in Further aims. objects land advantages of this the vicinity of the airport giving the airport con invention will Aappear from a. consideration of the description which follows with accompany trol ofñcer visible indication of altitude and di rection of all planes in the vicinity of the port. ing drawings showing for purely illustrative pur- ' For carrying out the above objects, the inven 25 poses embodiments of this invention. It is to be tion more broadly provides a method of com understood, however, that the description is not munication for continuously informing a remote . to be taken in a limiting sense, the scope of the _ station of certain data of variable magnitude‘by invention being defined in the appended claims. Referring to the drawings: ~ causing the carrier frequency of a radio signal collision in mid air especially during blind flying to be changed in response to one variable and, in 30 - Flg.- 1 is a diagrammatic illustration of the principle of this invention showingtwo airplanes case of transmission of several variables. t0 cause the carrier frequency to be modulated in addi each equipped with a transmitter and a receiver ' tion by one or several modulation frequencies. according to this invention; The invention further aims at providing suit Fig. 2a is a diagram illustrating the signals' able apparatus for practicing this method. - 35 transmitted by plane I of Fig. 1; It is thus a further and more specific object of this invention to provide a transmitter for use on aircraft including means for changing its car Fig. 2b is a diagram >illustrating the band of frequencies covered by the receiver of plane 2 of Fig. 1: ' ' rier frequency tuning in response to changes in Flg. 3 is a block diagram illustrating the oper altitude, for example by means of an altimeter, 4d ation of a transmitting and receiving unit accord-p ï and including means for modulating the variable carrier frequency in response to azlmuthal direc ing to this invention; tion, for example by means of a compass or a trative form of circuit of a transmitter and re Fig. 4 is a circuit diagram showing an illus ceiver for altitude signals; directional gyroscope. It is a further purpose of the invention to pro 45 Fig. 5 is a perspective view of an' altitude con vide a receiving apparatus capable of interpret trolled tuning element of the transmitter and re ' ceiver of Fig. 4: _ ing such signals. ÍFig'. 6 is a perspective view of a motor con- The invention thus aims at providing a receiv ing apparatus capable of scanning a certain band trolled tuning element of the receiver of Fig.'4; of carrier frequencies for signals and interpret 50 Fig. 'l is a circuit diagram showing a transmit ing the carrier frequency of received signals in ter and receiver for the transmission and recep „ tion of directional signals; and ‘ terms of the transmitted variable, such as alti Fig. 8 isa perspective view of a tuning ele tude. More particularly, the invention aims at pro ment of the transmitter shown in Fig. 6. vidìng a receiving apparatus capable of auto 55 'I_'hc principle of this invention will readily be 2,403,803 understood from the diagrammatic illustration of Fig. 1. It may be assumed that a ñrst plane In the illustration the primary tuning elei‘nent I4' is automatically adjusted by an altitude re sponsive device represented by an evacuated aneroid capsule IB'. plane is in its proximity at an altitude of 12,500 Assuming that a band of frequencies corre feet. In order to avoid collision between the two sponding to a range of altitudes of plus/minus planes, the invention provides a method and 1,000 feet relative to the altitude of the receiving means whereby the planes may exchange infor plane is to be scanned for signals, the altitude mation as to particular night data which will ' responsive device i6' will tune the receiver Ra enable each pilot to steer his plane clear of the 10 to the highest frequency of the band. In the other plane. illustrated example, the frequency of 49.35 mega Plane l is shown as equipped with a transmit cycles corresponds to the altitude of 13,500 feet. ter T1 and a receiver R1. The transmitter and A secondary tuning element shown as a vari receiver of the n_rst plane are provided with an able condenser i5' is mechanically operated by tennas i and ll respectively. A tuning element suitable means such as a motor M' for tuning in the transmitter Ti which may be a variable the receiver R2 successively to all frequencies is at an altitude of 13,000 feet while a second condenser l2 is controlled by an altitude respon sive device diagrammatically illustrated as an A from 49.85 to 49.15 megacycles thereby scanning the range of altitude from 13,500 to 11,500 feet. The frequency band is indicated in Fig. 2b by The dash-dot line in the center of the transmitter in dependence on the altitude at 20 shading. shaded band represents the altitude of the second which the plane l flies., plane which is 12,500 feet. The incoming signal In Fig. 2a there is shown how a band of fre of the ñrst plane is represented as a series of quencies may be co-ordinated with a range of dashes 2 and falls well within the band scanned altitudes. In the illustrated form of the inven ` ~ tion a band of carrier frequencies extending from 25 by the receiver R2. As hereinbefore stated, the instantaneous 48 to 51 megacycles is used to cover altitudes from tuning of the receiver is dependent upon the zero to 30,000 feet. adjustment of the secondary tuning element, for The transmitter of `the plane I ñying at an example. the angular position of the rotor plates altitude of 13,000 feet will, according to the chosen of the condenser l5'. Therefore, the adjustment 30 coordination of frequencies with altitude, trans of the secondary tuning element at the instant mit signals of a frequency of 49.3 megacycles. of reception of a signal is representative of the The signals may be transmitted periodically and altitude of the plane from which the signal are represented in Fig. 2a by dashes 2 parallel originates relative to the altitude of the receiving evacuated aneroid capsule i3. The tuning ele ment l2 changes the carrier frequency of the to the time axis. _ . These signals are picked up by the second plane 35 plane. As Will be outlined in greater detail below, an which is equipped with means for interpretating indicator may be associated with the movable the signals in_terms of altitude. This is accom member of the secondary tuning element, in the plished by automatically scanning a relatively illustrated example the rotor plates of the narrow band of carrier frequencies coordinated condenser l5', to indicate the altitude of the 40 to the altitude of the receiving plane. For this transmitting plane relatively to the receiving purpose a receiver is provided for picking up plane. any signals transmitted by planes flying at ap The scanning of the frequency band corre proximately the same altitude as the receiving sponding to the desired/'altitude range relative plane. As a practical example, the receiver may 45 to the altitude of the receiving plane maym be be so adjusted as to respond to all signals trans repeated at any desired number of cycles per mitted by planes flying within a predetermined unit oi time. i ' distance of about five or ten miles and at an alti I have found it convenient to traverse the tude differing from the altitude of the receiving tuning range approximately ten times per second plane by less than 1,000 feet altitude. 50 which would correspond to «a rate of rotation of To this end, the receiver of each plane isthe rotor shaft of the condenser l5' of ten revo equipped with a primary and a secondary tuning lutions per second, or 600 revolutions per minute. element. The purpose of the primary tuning ele An indicator such as a glow lamp operated by ment is to set the receiver for a carrier fre the receiver Rz will, accordingly. be actuated ten quency in dependence on the altitude of the .55 times per second by- a signal Picked up by the receiving plane. The secondary tuning element permits periodic receiver. l This arrangement will be further illustrated in the succeeding detailed ñgures of scanning of a relatively narrow frequency band the drawings. corresponding to the altitude range in which the From the foregoing it will appear that during presence of other planes is to be ascertained. In -60 each scanning cycle the receiver will also be the illustrated embodiment, the altitude range is tuned to the frequency of the transmitter with chosen tc extend from plus 1,000 feet to minus which it is associated in the same plane. Since 1,000 feet with respect to the altitude of the it is undesirable to pick up a signal from the receiving plane. transmitter with which the receiver is associated, Referring now to Fig. 1 the transmitter and in other words, since it is undesirable to pick up receiver of the second plane correspond in all particulars with the transmitter and receiver of ‘the signal of the transmitter T2 by the receiver R2 during each tuning cycle, means are provided for protecting the receiver from signals of the the~ñrst plane. Primed reference numerals are associated transmitter. . accordingly used for denoting the elements of Many forms of means and circuits are known 70 the second plane. in the art of electric communication which may The transmitter T2 is equipped with a trans b'e employed for this purpose. mitting' antenna I0', the receiver R2 includes an In the embodiment of the invention described antenna I I’. A primary and a secondary tuning hereinafter in greater detail, I employ mechani element is provided for tuning the receiver R2 75 cally operated means for silencing the trans to the desired frequency. 2,403,603 5 mitter for the period of time during which the receiver would respond to the signal of the associated' transmitter. ' This may conveniently be accomplished by - 'Finally the ‘received signal vmay be interpreted in terms ofr volume in_order lao-determine change'in distance from the'transmitting station. Referring now -to Fig. 3„ the transmitter T in means of blanking keys S1 and Si' operated by cludes a tuning element shown as a variable con the motors ,M dhd M', respectively, for inter el' denser I-'2 y for controlling the carrier frequency rupting the Í„transmitter signals while the .associated receiver is scanning the frequencies close lto the transmitter~ frequency.„ This l of a signal'emitted by the-antenna I D. _ 'I’he‘tun- - ing element is controlled by an altitude responsive means ~shown as an> evacuated diaphragm I3. signals from other planes flying in the vicinity '10 The carrier may be modulatedto give the sig nal a distinct characteristic. A modulator- Sz for at-the same altitude. modulating the carrier frequency is shown in the The _communication method and system form of >a rotatable interrupter disk I1 mounted according to this. invention pe ‘ts simultaneous on a shaft I8 of a motor 23. The disk Il includes transmission of several variables to a receiving insulating sectors 20 and rotates between brushes station. arrangement permits undisturbed reception 0f Illustrating this feature by reference to - a communication method and system for aircraft, it is possible to transmit,-in additionto informa tion regarding altitude, further data, such as 2I and 22 periodically-to interrupt the flow of current between the same.` I Turning -now to the receiver R, an incoming signal-is pickedr-up by :thefantenna II. The re as hereinbefore explained, includes apri direction of flight, or course of the transmitting 20 ceiver, mary and a secondary tuning'element shown as' ' I variable condensers I4 and I5. The condenser I'4 Fig. 3 illustrates in the form of a block is adjusted in response to altitude by an altitude u diagram the structure of a device for practicing' responsive element illustrated as an evacuated the method for communicating a plurality of diaphragm capsule IVG. ~ . variable data. A_ secondary tuning element shown as a4 var Referring ñrst to the method, a signal is plane. transmitted and the carrier `frequency of the signal varied within the limits of a predetermined bandof carrier frequencies in dependence'on a first variable, such as altitude in the -pres'ent specific example, The carrier may further be modulated by a predetermined fixed or variable modulating fre quency. A variable modulation mayßbe` im pressed on the carrier in response to the azi muthal direction of the pli-.ne transmitting- the iable condenser I5 is periodically operatedby the ‘ e motor 23, a shaft 24 being shown driven over a gear train 25 from the motor shaft I8. The con denser I5 is preferably/ of the type in which the capacity increases gradually during the greater part ofone revolution andl which after reaching a maximum capacity may be' brought to its mi'n imum capacity position by further rotation through a; relatively small angle. One form of condenser having this character- ' ~ istic is known as a “270°-condenser” and is so~ con signals. "I'his variation may be cyclic, that is to structed as to increase its” capacity during 270° of say, in traversing the entire azimuth circle from ~ rotation of its rotor from a minimum to a maxi north via east, south and west to north, the AFurther rotation of the rotor plates modulating frequency may be caused to increase 40 mum. through anangle of 90° will restore the condenser during one-half of the azimuthal circle and be to the-position of minimum capacity. caused to decrease again during the other half of The capacity of the condenser I5 is preferably the circle. For example, there may be caused' an ladded to that of the condenser I4, thereby chang increase in frequency from a minimum to a max ing the tuning of the receiver successively imum for directions between north and south through a predetermined band of carrier frequen through east. The modulation frequency may cies. The upper limit oi’A the band is fixed by the then be decreased again for directions within the sum of the capacities of condensers I4 and I5 second half of the azimuthal circle including. when condenser- l5 has its minimum position, the west. . in order to eliminate ambiguity arising from 50 lower limit- by the sum when condenser I5 is at the cyclic increase and decrease in the- modulation A signal of a frequency Within the band maximum capacity. frequency, a further and ñxed modulation fre- ' quency may be impressed on the ca_rrier for dl rections within one-half of the azimuthal circle. ‘I‘his modulation may be of a higher frequency. No such distinguishing modulation being pro . » , . .„ scanned by the receiver R is amplified by an am-l pliner A and- utilized for actuating an indicator. The altitude indicator is shown in the illustrated embodiment :to include _a glow- lamp 26. . A band pass filter F1 may be interposed be vided for the- other half; signals representing east. tween the amplifier and the indicator to elim and west-course become distinct although. ac inate interference. by radioïsignals of :other than cording to the present example, the variable mod ulation frequency assigned to west is the same as 60 a predetermined distinguishing frequency. The filter in the illustrated` embodiment is tuned to the one assigned to east. " the frequency of the modulator Sz, the same dis The modulated carrier frequency may further tinguishing modulating frequency being used' by ` bemodulated, preferably at a relatively low fre-, all planes. A A . \ quency, in order to give all transmitted signals a; During each tuning cycle a-»received signal will particular characteristic enabling filtering of the _cause .the glow lamp 26 to light once. 'The glow signal at a receiving station in order to eliminate lamp will respond’at the exact moment at which stray signals or interferences. ` the >receiver is tuned to the carrier frequency of A signal formed according to this method may ’ the particular signal. ' The angular position of > be interpreted at the receiving station as to the various data transmitted by the signal. The car 70 the rotor- of the tuning element l5 at theinstant rier frequency represents one variable, s'uch- as . altitude. In addition, the received signal may include further variables such as direction of f flight represented by modulation frequencies. 475 ofreception of a signal thus becomes a measure ofthe carrierfrequency of the signal. -Indicat _ing means are provided for indicating this posi ' tion. In the 'i'uustratedembodinient a rotatable disk _ 2,408,603 Further data. may be transmitted by4v the same 21 is mounted on the'motorshaft I8. The ‘ro tatable disk carries a marker or pointer 28 which may be painted thereon to cooperate with the graduations of a ñxed dial 29 preferably grad uated in feetof relative altitude'. The glow lamp‘26 preferably provides the sole signal by additionally modulating the4 signal in dependence on such data. In the illustrated form of the invention, means are providedl for .trans mitting information regarding the azimuthal di rection of the Etransmittinf.; plane` by modulating the signal in response to azimuthal direction. illumination for vthe indicating means. At the instant of reception of a signal the glów lamp will A modulator Ma is shown for this purpose con‘ trolled by a. directional instrument, in the illus light to render the momentary position of the ' pointer 28 visible` relatively to the dial. Assum 10 trated embodiment, a compass magnet. Referring now also to 8. the modulator ing the rate of` rotation of the rotor shaft to be includes an inductance coil 35 wound lsubstantial ten revolutions per second, the lamp 26 will light ly in the Íforni of a triangle and curved so »that~ its hypotenuse forms a circle .normal -to the curved area oi the triangle. The coil 35 is acted upon by a movable mass 38, preferably of iron, adapted to modify the inductance of the coil. The mass te is mounted for rotation on .theshaft ten times during each second giving the appeal’ ance of the pointer 28 to be stationary due to the resulting stroboscopic eiîect. The scanning cycle ymay be assumed to begin at the moment when the condenser I5 is in the position'of greatest capacity. Since the motor 23 runs at a substantially constant speed, the » 3l by means or an arm 08. The shaftvßl'is ro tatable in bearings as and 48. A direction re spons'ive element shown as a pair of magnets“ mounted on the shaft by means of arms I2 and scanning cycle is completed within a predeter-I mined time, for erample, one tenth ot a second during which the pointer 28 makes a full revó 48 maintains the mass 38 nxedin azimuth. A lution. The relationship in point of time of the mass M may be provided to counterbalance the periodic reception of a signal, also called time ` " ` phase of the signal, with respect to a ñxed zero 25 mass 3a. As the craft turns in azimuth the inductance point of the scanning cycle, for example the in will be caused to rotate relatively to the'mass 30 stant at which the condenser l5 assumes its about the axis of the shaft 31 thus causing the greatest capacity, thus becomes a measure of the mass to act on a wider or narrower area.of the carrier frequency of the signal in the illustrated arrangement and, accordingly. of the altitude of 30 inductance 85. rll'his movement causes the fre» the transmitting plane relatively to the receiving quency of the modulator to increase and decrease depending on the direction of relative movement. plane. . The device may be so adjusted that the mass In the illustrated embodiment, the graduation 36 is opposite the narrowest partl of theiinduc of the indicator is spread over an arc of 270°, a tance while the craft is headed north. The mass 270° condenser. I5 being used in the receiver R. will move into a position opposite the widest part The condenser will be described in greater detail of the inductance if the craft changes its course by 180°. This movement will cause the frequency In the drawing the pointer is shown in a po of the modulator to decrease from a maximum sition of plus 400 feet altitude indicating that a signal is being received from a plane flying l1:00 40 to a minimum. If the craftV continues to turn in the same direction the modulating frequency feet higher than the receiving plane. will again increase to assume al maximum after Since the condenser l5 after reaching its maxi the turn of 360° has beencompleted. ` . mum capacity is rotated further into the posi The range of modulating frequencies is pref tion of minimum capacity, the lamp will light again during the remaining 90° of rotation of 45 erably so selected that it may be covered by one scale of a frequency meter. A suitable range the condenser and the indicator. It is for this would be 500 to 700 cycles. ^ reason advantageous to provide a. blanking sector The cyclic change in the modulating frequency 30 of 90° covering the marker or pointer 28 dur entails an ambiguity since the same `modulating ing the 90° movement from minimum to maxi frequencies are co-orclinated with either half of mum capacity of the condenser. The glowing of the azimuth circle. This ambiguity may be elim the lamp Z-l during the 90° movement of the con inated by impressing a further and distinguishing denser into its position of maximum capacity thus below. - ‘ becomes unnoticeable. . modulation on the signal during one-half of the ' It will be noticed that the mark in the center of the graduation 'represents a. relative altitude 55 azimuth circle. diiîerence of zero. A signal causing the lamp to light at this point will be a signal of the same carrier frequency as the one transmitted by the transmitter T associated with the receiver. Means further inductance coil 45 curved as to form a In the illustrated embodiment this means is shown in the form of a blanking key Si com prisingl'a disk ofi conducting material 3i includ ing an insulating sector 32. The insulating sector frequency on the carrier »when the azimuth lies in a chosen half of the azimuth circle herein chosen to be north to south through east. The is soïarranged with respect to contact brushes 33 and 34 as to out oiï the transmitter while the Referring now to the receiver, an indicator may be provided for indicating the data transmitted as variations in modulation. frequency. In the ' In the illustrated embodiment thereis shown a half cylinder. The coil is coupled with indlict»Y ance 35 so that when the iron~ mass 36 is opposite _ the coil 45 there is suiïicient mutual induction to < are therefore provided for preventing the receiver 60 allow relay fili to .be energized. Relay 48 controls, a. further modulator S3 shown in the illustrated from responding to the signals of the transmit embodiment as including a disk 41 mounted on ter with which it is associated. the motor shaft i8 and having alternateconduct Such means may take the form of a Switch ingand insulating sectors 48 and 49 respectively. or other device for rendering the transmitter in The disk is shown as moving between brushes operative during the period of time during which 50 and 5l. ' the receiver would respond to the signal of the This modulator will impress its characteristic associated transmitter. ìiioin'êegr 28 passes thezero mark on the gradua frequency may be 3,000 cycles. «» A 75 illustrated embodiment there is shown‘an indi D 2,463,603 . 9 _ cator 52 having two pointers 53 and 54 movable over dials 55 and 56 respectively. The dials bear frequencies in a manner hereinbefore described. One-half ofthe indicator dial is rendered visible at a time, the distinguishing lamp 51 or 56 being The pointers 53 and 54 are jointly actuated from the movable element of a frequency meter lit through the selector relay 59, ' later to be described in greater detail. The fre' quency meter is connected to the amplifier A of the receiver R preferably' through a band-pass ñlter Fn permitting only frequencies of the mod to move in opposite directions. ' ' 10 azimuth direction co-ordinated to the modulating directional graduations. eachl dial covering one half of the azimuth circle. ulator M2 to pass through, in the illustrated form of the invention, frequencies between 500 and '700 cycles. 'I'he pointers 53 and 54 are connected y frequency of the incoming signal in terms of 10 . At the same time the receiving` plane transmits its own altitude by changing the carrier frequency of the outgoing signals in response to changes in altitude. c , ‘ 'l'he receiver associated with the transmitter is protected Vfrom the outgoing signals through the - blanking key Si interrupting the transmitter While the associated receiver is scanning the fre Means are provided for distinguishing 'between quencies close to the transmitter frequency, thus the two halves of the azimuth circle to which permitting reception of incoming signals of the equal bands of frequencies are co-ordinated. In same frequency at which the transmitter `oper the illustrated embodiment 'of the invention, ates. transparent dials are employed lighted by one or Exact synchronism between communication the other of a pair of bulbs 51 and 58 selectively 20 sets of different planes is avoided by slight dif lighted through a selector relay 59. The selec ferences in the rate of the motor 23. In the ab tor relay may be combined with a band-pass ñlter sence of synchronizing means,- the motors 23 of Fà permitting only frequencies of the distinguish different planes will operate at slightly din'eren't ing modulator 41 to pass through, in the illus speeds preventing a condition to exist -for an ap trated form of the invention, 3,000 cycles. o 25 preciable length of time in which the transmitter Information regarding a change in distance of . of a second plane in the vicinity is silenced exact’-` a transmitting plane from the receiving plane 1y` during the period of scanning of the frequency may be obtained by means of a distance indi band within which the frequency of the trans cator 60 which may be of the volume responsive mitter of the second plane lies. Temporary syn type employed in radio receivers. The distance 30 chronism may thus exist during a few seconds indicator is shown to be connected to the receiver only. . and includes a pointer 6I movable over adial In Fig. 4 lthe wiring diagram of a communica 62 preferably graduated in units of distance. A tion device is shown for transmitting altitude sig setting marker 63 may be provided, adjustable by nals. The device includes a transmitter and a, means of a setting knob 64, to permit an easy receiver. ' ' i reading of a change in volume of an incoming Referring ñrst to the transmitter, the antenna signal. After setting into a position opposite circuit includes a doublet antenna I0 and an in of the pointer, the movement of the pointer rel ductance 65. .The antenna coil is coupled with atively to the setting marker in response to the oscillator circuit in a suitable manner, in the changes in volume of the signal will 'be a meas 40 illustrated -embodiment there being shown a plate ure of the change in distance from the trans inductance 66 and >a. grid inductance 61 onefor mitting plane. An increase in volume, causing the pointer to move to the right, therefore indi cates a decrease in distance, while a movement in the opposite direction, towards the end ofthe dial, marked infinite, indicates that a transmitting plane moves away from the receiving plane. The operation of the device illustrated- in Fig. 3 is as follows: ‘ The transmitter T transmits a signal, the car both of which are inductively coupled with the antenna inductance. The coils 66 and 61 are connected by blocking condenser 68. The oscil lator is supplied with energy by a 'thermionic tube 69_and is controlled :by a suitable tuning ele ment, there being shown a variable condenser I2 .l n mechanically connected to an altitude responsive diaphragm I3. The tuning element I2 changes 50 the carrier frequency of the transmitter in de rier frequency of which is changedin dependence pendence on the altitude to which the diaphragm ' on changes in altitude ofthe transmitting plane I3 responds. as hereinbefore described. . A second plane or station equipped with the same communication device will pick up the sig nal with its antenna II. The receiver R of the receiving station is -tuned to a frequency co-or dinated to the altitude of the receiving plane and through its mechanically operated tuning ele The altitude controlled condenser is shown in greater detail in Fig. 5. The diaphragm I3 actu ates the rotor plates 10 of the condenser I2 by ' means of a pinion 1I and a, toothed sector 12 to which the center piece 13 of the diaphragm is connected by means of a link 14. In order to give a distinguishing characteristic 60 to the altitude signals, the transmitter output responding to a predetermined altitude band may be modulated by a characteristic frequency. above and below the altitude of the receiving In the illustrated form ofthe transmitter there plane. is shown a modulator Sz including the motor The altitude indicator of the receiving plane is driven disk I1 having insulating sectors 20 im `iointly actuated by the received signal and the bedded therein. The disk is driven by the motor mechanically operated tuning means to indicate 23 through the shaft I8 and moves between the carrier frequency of a received signal in terms brushes 2l and 22 therebyA changing the grid bias of altitude in a manner hereinbefore described. of the'thermionic tube at a suitable frequency Upon reception of a signal the setting marker 63 which may 'be of the order of about 100 cycles. of the distance indicator 60 may be set at a posi 'I‘he grid leak may consist oftwo resistances .15 tion opposite of the pointer 6I to determine and 16. The resistance-15 lies parallel to the changes in distance of the transmitting plane. brushes 2l and 22 of the> disk and is short cir At the same time the azimuthal direction of cuited periodically to reduce the grid leak to the motion of the transmitting craft may be read at value of the resistance ‘Iiil thereby modulating the the azimuth indicator indicating the modulating carrier of the transmitter. Preferably resistance ment I5 scans a band of carrier frequencies cor aeoaoos 4 l1 12 . „ i In Fig. '7 a communicationl‘device is'shown ‘I5 is greater than ‘I8 in order to secure deep mod ulation. The transmission of signals is periodically in terrupted while the associated receiver scans fre quencies close to the carrier frequency at which the transmitter operates. For this purpose there for transmitting in addition to information re by the plate battery il. successive conducting and insulating laminations' garding altitude further information Vregarding the course of ithe airplane. The transmitter circuit is similar to the one described in Fig. 4 except for the provision of an additional grid leak 88 forming part of a modulator Se for im is shown the blanking key S1 including a disk 8| pressing on the carrier an additional frequency having an insulating sector 32 and moving. be for distinguishing between the two halves of the tween the brushes 33 and 34. The interrupter Si azimuth circle. The grid leak 88 is periodically operates to interrupt the plate voltage supplied 10 short-circuit.-d by the interrupted disk 41 having t For reasons of simplicity, the heating devices 08 and d0. The disk which is driven by the for the cathode, such as for example the filament motor shaft I8 cooperates with brushes 50 and battery, are not shown in the wiring diagrams. 8| connected to the grid leak 88 through a relay Referring now to the receiver, the antenna coil 15 08. The relay may be of conventional ther 10 of the doublet antenna l I is coupled to the mionic type and includes a make-contact 89 for oscillator circuit of the receiver by means of a rendering the modulator S'a operative. The grid inductance 'I9 in the oscillator circuit; The make-contact is operated 'through the output of constants of the detector circuit of the receiver, tube 90 controlled by the inductance more particularly the magnitude of the grid leak 20 a,¿lethermionic which forms part of the device shown in Fig. 00, are so chosen that its self-oscillations are 8 for modulating the signals in response to periodically interrupted in a manner causing azimuthal direction. super-regenerative action at a frequency above Preferably, the grid resistor 88 is made small the range employed at the transmitter, this being. as compared to resistors 'I5 and 16 in order to in the illustrated form, frequencies of more than 25 maintain the carrier output substantially con 3,000 cycles. The detector circuit includes a stant regardless of whether the modulator S3 is thermionic tube 8i having a plate inductance 82 in operation or not. So proportioned, a dis-> connected thereto, the other terminal of the plate tance indicator operating on 4the volume meter inductance |being connected to the plate induct ance 'I9 through a blocking condenser 88. The 30 principle will remain practically unaffected by the modulator S3. ' plate circuit is completed’ through an amplifying The relay @i0 further includes the' usual grid transformer 80 and the plate battery 85.' ‘l bias battery 8i and plate battery S2. The relay The resonant frequency of the detector circuit is actuated in response to the movement of the is controlled by two tuning elements. the primary tuning being effected by a tuning element oper 35 mass 36 with respect to the inductance 45 for directions within one-half of the azimuth circle. ated in response to altitude. For directions within one-half of the azimuth In the illustrated embodiment, there is shown circle the make-contact 89 will be closed, there a condenser lé! operatively connected to an by rendering the modulator S3 operative. For evacuated diaphragm I6 in a manner illustrated directions within the other half of the azimuth in Fig. 5. A secondary tuning element shown as circle, the make-contact 89 will be open and the a condenser i5 is mechanically operated from outgoing signals will not be modulated by the a shaft 'it to permit periodic scanning of a band modulator Se. ` of carrier frequencies in the manner herein before described. The condenser I5 is preferably of the 270° type as shown in Fig. 6. The condenser has stator and rotor elements 88 and 8l so shaped that a rotation of the shaft 24 will cause a gradual increase or decrease in capacity during a rotary movement of 270°. After reaching the position of maximum or minimum capacity, the condenser is restored to its position of min imum or maximum capacity, respectively, by further rotation of 90° in the same direction. The condenser I5 operates periodically to de crease the resonant frequency of the detector` so as to effect scanning of a, frequency band of A variable modulation frequency is impressed on the signal in response to azimuthal direction. The azimuth modulator M2 operates preferably within the range of five to seven hundred cycles and includes the inductance 35 hereinbefore described in connection with Fig. 8 having a. tap intermediate its terminals. > The azimuth-responsive modulator M con stitutes an oscillator of the “Hartley" type, well known in` the art, and includes a thermionic tube 83, a grid leak 8l and condensers 95, 9S and 91. ` The output of the azimuth responsive modu lator‘may be amplified by an amplifier includ ing a thermionic `tube 98. The amplifier is shown to'be of conventional form and includes a frequency associated with plus/minus 1,000 feet of altitude dißerence with respect to the 60 further a volume control 99, a bias resistance |00 and a' coupling condenser IOI. AA coupling altitude of the airplane on which the receiver is transformer |02 is provided to modulate the- ' used. Referring to the chart 2b, the width of ` transmitter. ' the band is .2 megacycle. Referring now to the receiver, the detector 'The detector circuit operates through an amplifier A of conventional structure. an indi 65 -and amplifier circuits as well as the altitude in, dicator are not shown in detail in this flgure. cator of the form hereinhefore described. Pref The direction indicator 52 may be connected to erably there is interposed between 'the receiver the receiver through band-pass filters F2 and` and the indicator a band-pass filter F1 of con? Fa which are of conventional construction and ventional structure permitting only signals toV pass through which have the characteristic 70 will, for this reason,not` be further described. The band-pass ñlter` F2 is tuned to permit modulation impressed by the transmitter, in the only the frequencies to pass therethrough which illustrated form of the invention this being a are modulated in response to changes in modulation frequency of 100 cycles. 'I'he ele azimuthal direction, in the illustrated embodi ments of the band-pass ñlter are conventional and will, for this reason, not be further described. 75 :ment frequencies between 500 and '100 cycles. predetermined width. A suitable band includes 3,403,603 ' 13 . The filter F: is so tuned as to permit only dis tinguishing frequencies to pass through, in the illustrated form of the invention frequencies of about 3,000 cycles for actuating the selector relay 5_9. 5 The selector relay includes a movable arma craft which includes transmitting wireless signalsof a carrier frequency lwithin the limits of a pre determined band; varying said frequency within said band in dependence on the altitude of the transmitting craft; modulating said carrier fre .quency by a modulating frequency; and ,varying said modulating frequency in dependence on the ture |03 cooperating with a pair of contacts |04 and |05 for supplying current to lamps 51 and 50 azimuthal direction of flight of said transmitting 'respectively from a battery |00. The lamps 51 and 58 illuminate opposite halves 10 2. The method of communication between air of the directional dial 55, a member |01 being craft which includes transmitting wireless signalsprovided to prevent light from one bulb from .of a carrier frequency within the limits of a pre illuminating the other half of l»the dial. determined band; varying said frequency within ’I‘wo pointers 53 and 54 are movable relatively said band in' dependence on the altitude of the to the dial to indicate direction. 'I'he pointers 15 transmitting craft; modulating said carrier fre craft. 53 and 54 are connected to an actuating member to move in opposite directions. ` » ` ' quency _by a first modulating frequency; varying said first modulating frequency in dependence on ' In the illustrated embodiment there is shown a movable element |08 having a shaft |09. A gear the azimuthal direction of flight of the trans mitting craft over yboth halves of the azimuth |I0 on the shaft |00 meshes with the pinion |||- 20 circle; and modulating said carrier frequency by on the shaft of the pointer 54. A second pinion a second modulating frequency during o_ne half ||2 on the shaft of the pointer 53 meshes with of the azimuth circle. pinion ||| to move the pointer 53 in the opposite 3. In a communication system for aircraft; `direction. The gear train ||0,_ | || is employed in means responsive to the altitude of the craft; a order to amplify the limited movement of the ele radio transmitter controlled by said altitude rement |00 to a movement of approximately 180° sponsive means for transmitting signals of acar for actuating the pointers in order to obtain a dial rier frequency proportional to the altitude ~of thesimilar to a compass dial. The movable element craft, said transmitter including means for modu |08 moves relatively to two field coils | I3 and ||4 lating the transmitter output; -and means re respectively. 30 sponsive to the azimuthal direction- of flight of One terminal of the ñeld coil H4 is connected the craft for adjusting said modulating means through a resistance | I5 to oneI output terminal of the band-pass ñlter. The corresponding terminal of the other field coil ||3 is connected to the for varying modulating frequencies in dependence on -the azimuthal direction. , 4. In a communication system Afor aircraft; other output terminal of the band-pass illter> 35 means responsive to the altitude of the craft; through an inductance H6. _ The two remaining terminals of the field coils are connected to a point between an inductance means responsive to thev azimuthal direction o_f . the craft; a radio transmitter controlled by said altitude responsive means for transmitting sig- . i H1 and a resistance ||8 leading to terminals nals of a carrier frequency proportional to the of the resistance ||5 and the inductance H5. 40 altitude of the craft, said transmitter including respectively. first means controlled by said direction respon~ An incoming signal, if modulated by a 3.000 sive means for modulating the transmitter signals cycle frequency, will cause one-half of the direc by a modulating frequency increasing for one half tional dial to be illuminated. If the'signal is not of the azimuth circle and decreasing for the other so modulated, the other half of the dial will be half of the azimuth circle, and second means illuminated. The movable element |08 will as controlled by said direction responsive means for sume a position relatively to the fleld coils | I3 and ||4 in dependence on the variable modulating additionally modulating the transmitter signals during only one half of the azimuth circle, where frequency representing azimuthal direction which _by altitude and direction of the craft' are distinctly . is thus indicated to inform the pilot of the course 50 communicated. y of other craft in the vicinity. 5. In a communication system -for aircraft the In many applications of the present invention, 4combination with a directionally, and altitude it is advantageous to restrict the operating range controlled transmitter for transmitting signals of of the transmitter and the receiver in order to variable carrier frequency in dependence on alti limit the response of the receiver to transmitters tude, and of variable modulation frequency in de within less than a. predetermined distance. This pendence on azimuthal direction of a craft; of may conveniently be done by limiting the output signal receiving means comprising, in combina of the transmitter, or the sensitivity of the re tion, periodically operated power means; a radio ceiver, or both, to avoid a response to signals of receiver including means operated by said power transmitters beyond the predetermined range. eo means for periodically tuning said receiver to suc In aerial navigation, for example, it is essential eessive frequencies, altitude indicating means only that a pilot be advised of flight data of other jointly operated by said power means and the out planes in his vicinity, while information about put of said receiver; a frequency responsive actu the altitude of remote planes is relatively unim ating element responsiveto the modulation fre portant since the danger -of collision in mid-air _quency of signals received by said receiver; and does not exist in the latter case. directional indicating means operable by said ac Obviously, the present invention is not re-. tuating element. ‘ stricted to the particular embodiments herein 6.v In a communication system for aircraft the shown and described. Moreover, it is not indis combination with a 'directionaily and altitude pensable that all the features of this invention be 70 controlled transmitter for transmitting signals of used conjointly as they may advantageously be 'variable carrier frequency in dependence on al employed in various combinations and sub-com titude,l and of variable modulation frequency in binations. ' dependence on azimuthal direction of a craft; of What is claimed is: signal receiving means comprising, in combina 1. ’I'he method of communication between air tion, periodically operated power means; an a1 2,403,603 of a signal is indicated by the instantaneous ro timeter; a radio receiver including primary and tary position of said rotatable element, the rotary secondary tuning means, said primary tuning position representing altitude difference of a means being connected to be operated by said al transmitting craft with respect to the receiving titude responsive means for tuning the receiver to a carrier frequency proportional to the altitude 9. A communicationdevice for aircraft as set of the receiving craft, said secondary _tuning forth in claim 8 in which there is additionally means being connected to be operated by said provided a modulating device driven by said mo power means for tuning said receiver during each tor and controlling said transmitter for interrupt cycle of operation to successive carrier frequencies within a frequency band of predetermined width 10 ing the transmitter output at a predetermined frequency; and a qfilter tuned to- the frequency of the frequencies of the band depending on the said modulating device, said filter being inter primary tuning; altitude indicating means jointly posed between said receiver and said indicating operated by said power means and the output craft. ‘ ' ' means for blocking from said indicating means of said receiver; a frequency responsive actuating element responsive to the modulation frequency 15 signals of other than said predetermined fre quency, thereby preventing erroneous actuation of signals received by said receiver; and direc of said indicating means by stray signals. tional indicating means operable by said actuat 10. A. communication device for aircraft com ing element. prising, in combination, a iirst craft provided '7. In a communication system for aircraft the combination with a directionally and altitude con 20 with an azimuth _direction indicator; a first mo tor adapted to run `at substantially constant trolled transmitter for transmitting signals of speed; a radio transmitter including a variable variable carrier frequency in dependence on al» tuning device; means responsive to the altitude titude, and of multiple modulation including mod of the craft for tuning the transmitter to a‘car ulation by a variable frequency in dependence on an azimuthal direction of a craft and“ addi 25 rier frequency proportional to the altitude of the craft, a ñrst modulator operable by said direc tional modulation by a fixed frequency for direc tion indicator for modulating the transmitter sig- tions within one half of the azimuth circle; of nais in dependence on the direction of the craft, signal receiving means comprising, in combina and a second modulator operated by said direc tion, periodically operated power means; an al timeter; a radio receiver including primary and 30 tion indicator for additionally modulating said signals by a predetermined fixed frequency dur 'secondary tuning means, said primary tuning means being connected to be operated by said a1 titude responsive means for tuning the receiver to a carrier frequency proportional to the altitude ing flight directions within one half of the azi muth circle; a switch operated by said motor for periodically rendering said transmitter inoper of the receiving craft, said secondary tuning 35 ative; a second craft provided with a receiver in cluding a first and a second tuning element; means being connected to be operated by said means responsive to the altitude of the craft for power means for tuning said receiver during each adjusting said first element to tune said receiver cycle of operation to successive carrier frequencies to a carrier frequency proportional to the alti within a frequency band of predetermined width the frequencies of the band depending on the pri 40 tude of the craft, a second constant speed motor for periodically tuning said receiver to succes mary tuning; altitude indicating means jointly sive carrier frequencies within. a predetermined operated by said power means and the output of band, thereby scanning said band for signals, the said receiver; a frequency responsive actuating location of the band being determined by said element responsive to the variable modulation fre first receiver tuning; an amplifier connected to quency of signals received by said receiver; means said receiver for amplifying its output; altitude responsive to said ñxed frequency; and directional indicating means including a rotatable element indicating means jointly operable by said actu driven. by said second motor, and a fixed element ating element and said fixed frequency responsive cooperating with said rotatable element, one of means. 8. A communication device for aircraft com 50 said elements being a glow lamp operated by said amplifier whereby altitude of the second prising, in combination, a motor adapted to run craft relatively to the first craft is indicated by at substantially constant speed; a radio trans mitter including a variable tuning device; means ' the rotary position of said elements at the in stant of lightingof said lamp; directional indi responsive to the altitude oi' the craft connected to said tuningdevice for tuning the transmitter 55 cating Ameans including a frequency responsive first actuating element connected >to respond to to a carrier frequency in dependence on the a1 the variable modulation frequency of incoming titude of the craft; a switch operated by said mo tor for periodically Írendering said transmitter inoperative; a receiver including a first and a sec signals,` a frequency responsive second actuat ing element connected only to respond to signals ond tuning element; means responsive to the al 60 modulated by said firstyfrequency, thereby dis tinguishing .between directions within the two titude of the craft for adjusting said first element to tune said receiver to a carrier frequency pro portional to the altitude of the craft, said second element being driven by said motor for periodically tuning said receiver to successive carrier fre quencies within a predetermined band, thereby scanning said band for signals, the location of the band being determined by said first tuning ele ment controlled in response to altitude; an am pliiier connected to said receiver for amplifying its output; and indicating means including a ro tatable element driven by said motor, and a fixed element cooperating with said rotatable element, one of said elements being a glow lamp operated by said amplifier, whereby the instance of receipt halves of ’the azimuth- circle, ' and indicating means operated by said actuating elements. 11. A communication apparatus for aircraft comprising, in combination: a transmitter of wireless signals; a device responsive to the alti tude of said apparatus for tuning said transmit terv to a carrier frequency proportional to the altitude of said apparatus, and means for modu latins said signals by a predetermined frequency 'to distinguish said signals over lstray signals; a receiver of wireless signals including filter means for excluding signals of other than said prede termined modulation frequency, whereby inter ference by stray signals is prevented; a device 17 responsive to the altitude of said apparatus l-for tuning said receiver to a carrier frequency pro portional to the altitude of said apparatus; power operated means for varying the tuning'of 18A of tuning of said receiver to the transmitterV frequency. said receiver through a band of carrier fre 14. A communicationl apparatus for aircraft comprising, in combination, a transmitter of wire less signals including a tuning element for tuning quencies bearing a predetermined relation with the tuning effected by said altitude responsive device; an altitude indicator jointly operated by said transmitter to transmit signals within a pre determined band of carrier frequencies, and an oscillator for modulating said signals by a pre said power operated means and by the output determined modulation frequency; an altitude of said receiver; and means operated by said 10 responsive device for operating said tuning ele power operated means for rendering said trans ment to tune said transmitter to a carrier fre mitter inoperative during the period of tuning quencyproportional to the altitude ofthe craft: of said receiver to the transmitter frequency. a receiver of wireless signals, said receiverin 12. A communication apparatus for aircraft cluding means for tuning said receiver to a car comprising, in combination, a transmitter of 15 rier frequency of incoming signals; altitude re wireless signals, said transmitter comprising a sponsive means for operating said tuning means first tuning element for varying the carrier fre to tune said receiver to a carrier frequency pro quency oi' said signals within a predetermined portional vto the ,altitude of lthe craft; power . band of carrier frequencies, and a modulating operated means for varying the tuning-of the oscillator including a second tuning element .for 20 receiver cyclically through a band of carrier fre varying the modulation frequency of said signals quencies bearing a predetermined relation to within a predetermined band of modulation fre the tuning effected by said altitude responsive quencies; a device responsive to the altitude of means; indicating means jointly operated by said the craft for operating one of said tuning ele power operated means and by the output ofsaid ments in dependence on the altitude of the craft; 25 receiver; filter means for excluding from said a device responsive to the azimuthal direction indicating means signals of a modulation fre of the craft for controlling the other of said quency other than that of said oscillator; and tuning elements in dependence on the direction means operated by said power operated means of the craft; a receiver of wireless signals Ain for rendering said transmitter inoperative dur cluding first power operated variable tuning 30 ing the period of tuning of said receiver to the means for tuning said receiver to incoming sig carrier frequency of the transmitter. nals of carrier frequencies within said prede l5. A communication apparatus for aircraft termined band, and second means for determin comprising, in combination, a' transmitter of wire- » ing the modulation frequency of incoming sig less signals, said transmitter including a tuning ' nals; an'altitude indicator; an indicator of azi muthal directions, one of said indicators being jointly operated by 'the output of said receiver and said ñrst tuning means, the other indicator signals within a predetermined band of carrier frequencies, and an oscillator for modulating said being operated by said second means; and means element for tuning said transmitter to transmit signals, the oscillator including a variable tuning device; means responsive to the altitude of the coupled with said first tuning means for render 40 craft for actuating said tuning element in de ing said transmitter inoperative during the pe pendence on`the altitude of the craft, whereby the riod of tuning of said receiver to the transmitter carrier frequency of the signals _becomes a meas frequency. 13. A communication apparatus for aircraft ure of the altitude of the craft; and means re sponsive to the azimuthal direction of the craft comprising, in combination, a transmitter of ' 45 for actuating said tuning device in dependence wireless signals, said transmitter comprising a ñrst tuning element for varying the carrier frequency of said signals within a predetermined :band of carrier frequencies, and a modulating os cillator including a second tuning element for varying the modulation frequency of said signals within a predetermined band of modulation fre quencies; a device responsive to the altitude of the craft for operating said ñrst tuning element; a device responsive to azimuthal direction of the craft for controlling said second tuning' element; a receiver of wireless signals including tuning means for tuning said receiver to a fre quency of incoming signals of carrier frequencies within said predetermined band; means respon-_ sive to the altitude of the craft for operating said tuning means to tune said receiver to a frequency proportional to the altitude of the craft; power operated means for varying the tuning of the receiver cyclically through a band of carrier frequencies bearing a predetermined relation to the tuning effected by said altitude responsive means; an altitude indicator jointly operated by the output of said receiver and on the direction of iiight of the craft, whereby the modulation frequency becomes a measure of the azimuthal direction of the craft. 16. A communication apparatus for aircraft 50 comprising, in combination, a transmitter of wire- n less signals, said transmitter including a tuning element controlling the carrier frequency of transmitted signals, a first' oscillator for modu-l lating said signals, said ñrst oscillator includ 55 ing a variable tuning device, and a second oscil lator tuned to a predetermined spot frequency; means responsive to the altitude of the craft for actuating said tuning element in dependence on the altitude of the craft, whereby the c_arrier 60 frequency of the signals becomes a measure of the altitude of the craft; means responsive to the azimuthal direction of thecraft for actuating said tuning device in dependence on the direc tion of flight of the craft, whereby the modula 65 tion frequency becomes a measure of the azi muthal direction of the craft; and means respon sive to the azimuthal direction of the craft for rendering said'second oscillator operative for di rections within one half of the azimuth circle said power operated means; means responsive to 70 and inoperative during the other half., the modulation frequency of an incoming signal; a direction indicator operated by said modulation frequency responsive means; and means coupled with said power operated means for rendering 17. The method of communication between air craft which comprises transmitting from a first craft a carrier wave, varying the frequency of said carrier wave according to the altitude of said transmitter inoperative during the period 75 said first craft, modulating said carrier wave by u .. u .. „. , 19 20 quencies, altitude indicating means including a rotatable element coupled to said rotatable a first modulating wave, varying the frequency of said first modulating wave according to the member and an element cooperating with saidv azimuthal direction of the nrst craft over both rotatable element to provide an indication, one halves of the azimuth circle, modulating said of said elements being actuated in response to carrier wave by a second _modulating wave dur the receiver output whereby the altitude of said ing only one-half of the azimuth circle, there transmitting craft is determinable from the by communicating the altitude and direction of relative position of the two elements at the in said first craft; receiving said communication stant of reception, direction indicating means on a second craft, said receiving comprising theincluding a ñrst modulation wave responsive steps of cyclically scanning said carrier wave 10 means operated by the output of said receiver in throughs. band of predetermined width, varying dependence upon the ñrst transmitted modulated the location of said scanned band according to wave to give over both halves of the azimuth the altitude of the second craft to derive an indi circle an indication corresponding to the direc cationof altitude of said nrst craft, and deriv tion of night of said transmitting craft, and ing anadditionalsignal from said first and sec second modulating wave responsive means ond modulations to determine the direction of said first craft. ’ responsive to said second transmitted modulating wave for visually. distinguishing between the i8. In va communication system of the char opposite halves of the azimuth circle. l acter` described including a transmitting craft 20. In a communication system for aircraft, 20 having a transmitter sending a carrier wave a first craft having a transmitter comprising whose frequency var-ies with the altitude of the means for transmitting a wave whose frequency transmitting craft, said carrier being modulated has a value dependent upon the magnetic by a first modulating wave; a receiving craft heading of the transmitting craft, the value of comprising periodically operated power means said frequency varying between maximum and 25 including a rotatable member, a radio receiver minimum as the craft’s heading changes from including means operated by said power means opposite points of the azimuth circle, said for periodically tuning said receiver to successive transmitter having means for transmitting a frequencies on a band of carrier frequencies, Wave of .a second and fixed frequency for altitude indicating means including a rotatable headings corresponding to one-half of the 30 element coupled to said rotatable member and azimuth circle between said opposite points: a an element cooperating with said rotatable second craft having a receiver comprising means element to provide an indication, one of said for deriving said first wave for indicating elementsv being connected to be actuated in headings between said opposite points, and means response to the receiver output whereby the alti for deriving said second frequency for determin 35 tude of said transmitting craft is determinable ing in which half of the azimuth circle said first from the relative position of the two elements means shall indicate. at the instant of reception, indicating means 21. In a communication system for aircraft, a including modulation wave responsive means ñrst craft having a transmitter comprising operated by the output of said receiver in de means for transmitting a carrier Wave, means pendence upon the transmitted modulated wave 40 for modulating said carrier wave with a modu of the transmitting craft. lating frequency having a value dependent upon 19. In a communication system of the char the magnetic heading of the transmitting craft, acter described including a transmitting craft the value of said modulating frequency varying having a transmitter sending a carrier wave whose frequency varies in proportion to the altitude of the transmitting craft. said carrier being modulated by a ñrst modulating wave between maximum and minimum vas the craft’s heading changes from true north to true south; said transmitter having means for modulating said carrier wave with a second and fixed modu whose frequency varies with the direction of lation frequency for headings corresponding to` night of the transmitting craft, said carrier Wave one-half of the azimuth circle between north and being modulated by a second modulating wave 50 south; a second craft having a receiver compris for ñlght directions within one half of the ing means for derivingsaid first modulating wave azimuth circle; the combination with a receiving for indicating headings between north and south, craft comprising periodically operated power means including a rotatable member, a radio receiver including means operated by said power means for periodically tuning said receiver to successive frequencies of a band of carrier fre and means for deriving said second modulating A55 wave for determining on which half y, of the azi- muth circle said ñrst means shall indicate. ARTHUR KORN.