Aug. 13.11, 3.942. H. K. MARKEY 222922.387 SECRET COMMUNICATION SYSTEM Filed June 10, 1941 2 Sheets?Shth 1 L. E. '056. 31; 500'" a so- laa~ 213 I 'zz vn R. 31.: FREQ UENCY CEERJER OSCIL IIHPLIFIER J7 ?condemn 43/ a? . 3? 424? a 24:7? 44? 34? 24g .243 4/ 50 0% . /ng. .I [004? 64? A 5. RECTIFIER /70 4,4: Jansen/a Mam/m 1; 55,5} 565 570 500'" FILTER RECTIFI: 7 r7 [Bil?TAT/call I 37 . Tm 37 AU, 7EmrEpo /03 Augo M, H. K. MARKEY ETAL. 2,292,387 SECRET COMMUNICATION SYSTEM Filed June 10, 1941 2 Sheets?Sheet 2 a. 4. air-gnusrzi?o'w/ r2? 33/ 55;: Patented Aug. M, 1942 2,292,387 UNITED STATES PATENT .OFFICE 2,292,387 SECRET COMMUNICATION SYSTEM Hedy Kiesler Markey, Los Angeles, and George Anthcil, Manhattan Beach, Calif. Application June 10, 1941, Serial No. 397,412 (Cl. 250?2) 6 Claims. This invention relates broadly to secret com- munication systems involving the use of carrier waves of diiferent frequencies, and is especially useful in the remote control of dirigible craft, such as torpedoes. An object of the invention is to provide a method of Secret communication which is rela? tively simple and reliable in operation, but at the same time is dif?cult to discover or decipher. Brie?y, our system as adapted for radio control of a remote craft, employs a pair of records, one at the transmitting station and one at the receiving station, which change the tuning of the transmitting and receiving apparatus from time to time, so that without knowledge of the records an enemy would be unable to deter- mine at what frequency a controlling impulse would be sent. Furthermore, we contemplate employing records of the type used for many years in player pianos, and which consist of long rolls of paper having perforations variously posi- tioned in a plurality of longitudinal roWs along the records. In a conventional player piano rec? ord there may be 88 roWs of perforations, and in our system such a record would permit the use of 88 di?erent carrier frequencies, from one to another of which both the transmitting and receiving station would be changed at in- tervals. Furthermore, records of the type de- scribed can be made of substantial length and may be driven slow or fast. This makes it pos- sible for a pair of records, one at the transmit- ting station and one at the receiving station, to run for a length of time ample for the remote control of a device such as a torpedo. The two records may be by driv- ing them with accurately calibrated constant- speed spring motors, such as are employed for driving clocks and chronometers. However, it is also within the scope of our invention to pe? riodically correct the position of the record at the receiving station by transmitting nous impulses from the transmitting station. The use of impulses for correct- ing the phase relation of rotary apparatus at a receiving station is well-known and highly de- veloped in the fields of automatic telegraphy and television. Other more speci?c objects and features of our invention will appear from the following de- tailed description of a particular embodiment thereof, as illustrated in the drawings, in which Fig. 1 is a schematic diagram of the appa? ratus at a transmitting station; 10 15 20 25 Fig. 2 is a schematic diagram of the appa- ratus at a receiving station; Fig. 3 is a schematic diagram illustrating a starting circuit for starting the motors at the transmitting and receiving stations simultane- ously; Fig. 4 is a plan view of a section of a record strip that may be employed; Fig. 5 is a detail cross section through a rec? ord- ?responsive switching mechanism employed in the invention; Fig. 6 is a sectional view at right angles to the view of Fig. 5 and taken substantially in the plane of Fig. 5, but showing the record strip in a di?erent longitudinal position; and Fig. 7 is a diagram in plan illustrating how the course of a torpedo may be changed in ac- cordance with the invention. Referring ?rst to Fig. i, there is disclosed a mother ship In which at the beginning of opera- tions occupies the position Inc and at the end of the operations occupies the position Inb. This mother ship discharges a torpedo II that travels successively along different paths I2strike an enemy ship II, which initial- ly' occupies the position [Ia but which has moved into the position at the time it is struck the torpedo ll. According to its original course, the enemy ship l1 wouldrhave reached the posi- tion ?le, but it changed its course following the ?ring of the torpedo, in an attempt to evade the torpedo. In accordance with the present invention, the torpedo II can be steered from the mother ship Illa and its course changed from time to time as necessary to cause it to strike its target. In directing the torpedo it may, under some cir? cumstances, be observed directly from the mother ship in, or its course may be followed by an observer in an airplane I8 who communicates his ?ndings to the mother ship ma. It is also possible to control the torpedo directly from the airplane [8 if the latter is equipped with the necessary transmitting equipment in accord- ance with the invention. Under the particular circumstances of Fig. 7, the enemy ship. l'l' was traveling in a straight line substantially parallel to the mother ship In at the time the torpedo was discharged, and the latter was directed forwardly at a substantial angle to compensate for the speed of the ship l1 and for water currents represented by the small arrows l9. -However, as a result of the change in course of the enemy ship Ila and the e??ect of the water currents, it is observed that 2 the torpedo, if it continues on its original course, will miss the enemy ship. Hence it is steered by remote control to depart from the path :2 and follow the path 13. At later times it is noted that further changes are necessary, and its course is successively changed from the path 13 to the path 14, to the path 15, and to the path in order to strike the enemy ship 11b. The rembte control of the torpedo as described is old and broadly does not constitute a part of our invention. However, it has been very dim- 10 cult in the past to employ radio control of a . torpedo, for the reason that the enemy could quickly discover the frequency of the control sig? nals and block control of the torpedo by sending false signals of the same frequency. In accordance with our invention, we employ variable frequency radio transmitters and .re- ceivers for the remote control, and change the frequency at intervals by records at the two stations. Referring to Fig. 1, the apparatus at the trans- mitting station includes as its main elements a variable-frequency carrier oscillator 29, a modue lator. an ampli?er 22, and an antenna 23. These elements are represented. schematically since their exact construction does not consti- tute a part of the present invention. Suf?ce it to say that the variable-frequency carrier oscil- lator .29 is controlled to oscillate at different fre-_ quencies by a plurality of tuning condensers 21a, 240, 21d, 293, 241?, and 24g, adapted to be independently connected to the oscillator by an- tomatically controlled switches 31, one for each condenser. The different Condensers 24a. to 219, inclusive, are of different capacities, and these differences are indicated in the drawings by dif-- ferent spacings between the plates. Two controls are provided in the system of Fig. 1, in the form of two keys and R, respec- tively. Key is employed to transmit a signal for applying left rudder to the distant torpedo, and the key is employed to apply right rudder to the torpedo. Actuation of the key closes main contacts 32, which connect the output of the oscillator 29 to the modulator and at the same time closes contacts 33, which connect a loo-cycle oscillator 31 to the modulator which thereupon modulates the particular carrier wave being generated at that time by the oscillator 29. The modulated carrier wave is then ampli- ?ed in the ampli?er 22 and transmitted from the antenna 23. If the operator desires to apply right rudder to the distant torpedo, he actuates the key R, which closes the main contacts 32 and also closes contacts 35, which connect a 500-cycle oscil? lator 38 to the modulator The switches 31 are selectively closed by a record-controlled mechanism actuated by a rec-. 0rd strip 31, which is drawn off, a supply roll a over a control head 39 and wound up on a take- up spool 59 driven by a constant~speed clock mo- tor Referring now to Fig. 4, the record strip 31 has perforations arranged in eight different lon- gitudinally extending rows and II, respectively. Perforations in the rows A, B, C, D, E, F, and control the seven switches 3 associated with the different tuning condens- ers 24a to 24g, inclusive. The perforations in row control an auxiliary switch 12 (Fig. 1), which lights a signal lamp 43 from a battery u. The strip is drawn over the control head 15 20 25 30 35 2,292,387 responds to perforations in the different rows A to H, inclusive, on the strip, to close the vari- 0115 switches 3 and the switch 42. A typical construction that may be used in the control head 39 is shown in Figs. 5 and 6. Thus it may comprise a block or shoe 15 over which the record strip is drawn and which has a plurality of vertical passages 46, the ori?ces of which are juxtaposed to the different rows A to H, inclusive, of the strip. In Fig. 5 two of the passages 15. are shown juxtamsed to and in com- munication with apertures in the two IOWS and of the strip 31. Each of the passages 46 is communicated by a restricted passage 41 with a suction manifold 48, which is connected by a tube 49 to a suctidn pump 59. Each of the passages 46- is also con- nected by a tube 5 to the upper end of an associated-cylinder 52 containing a piston 53. Each piston 53 projects from the lower end of its associated cylinder 52. and overlies a movable spring 54 of one of the tuning switches 31. The movable spring 55 is separated by a block of in- sulation 55 from the lower end of its associated piston 53. The pistons are normally maintained in upper position in which shoulders 55 thereon - lie against the lower face of the cylinder block . 51 containing the cylinders 52,-under which con? - ditions the contacts II are open. However, un? der certain conditions. to be described, the pis- tons 53 are urged downwardly, by compression springs 53a positioned thereabove, to carry the movable springs 54 against the cooperating con- tact springs 59 to close the switches The pistons 53 are maintained in uppermost . position, in which the switches 31 are open. 40 45 50 55 70 when a solid portion of the record strip 31 over- lies the passages but are depressed by the springs 53a. when apertures in the record strip move into registration with the passages IE. Thus so long as the upper end of a passage 46 is closed by the record strip 31, suction is ap? plied from the manifold 48 through the restrict-- ed passage to the cylinder 52, and lifts the piston 53 against the force of the spring 53a. However, when a perforation in the record strip is in registration with a passage 45, air flows freely into the upper end of the passage and into the restricted passage 41, thereby breaking the suction applied to the upper end of the piston 53 and permitting the spring 53:: to move the piston downwardly and close the associated switch It. It will be obvious that by so positioning the perforations in the different rows that perforations in different rows are successively brought into registration with their associated passages 46 (Fig; 5), different ones of the switches 3 will be successively closed, to= connect different ones of the tuning con- densers 21a to 249r (Fig. 1) inclusive, to the oscillator 29 and thereby change the frequency of the carrier wave. Furthermore the frequency changes can be purely arbitrary, without any periodic recurrence that would render it easy for an enemy to anticipate the frequency at any particular instant. Referring now to Fig. 2, the apparatus at the receiving station, (which may be on the tor- pedo of Fig. 1), comprises a receiving an- tenna SI and a signal selector 8 that may be tuned to any one of four different frequencies by connecting thereto different condensers 2l?d, 24?s, 24'1', and 2417. When the condenser 2rd 39, as previously mentioned, and the control head 75 is connected to the selector SI and the condenser 2,292,387 mm is connected to the oscillator 26, the trans- mitter and receiver are both tuned to the same frequency, and so on. When a signal received on the antenna 66 is of the same frequency to which the selector 6 is tuned, the signal is ampli?ed in. an ampli?er 64 and delivered to a detector 65. There will then appear in the output of the detector the modulation wave that was impressed upon the - carrier at the transmitting station, and this modulation wave is applied to the input of a pair of ?lters I66 and 566, the ?rst of which is tunedto IOU-cycles and the second to 500-cycles. The output of the ?lter I66 is delivered through a recti?er I68 to a magnet I69, and the output of the ?lter 566 is delivered through? a recti?er 568 to a magnet 569. The magnets I69 and 569 act on a common armature 12, which is nor- mally positioned in a neutral position but moves in responSe to energizatio'n of magnet I69 to close on a contact I16 and moves in response to energization of magnet 569 to close on a con- tact 516. If a received signal was produced by actuation of the key (Fig. 1) at the transmitting sta- tion, then it is modulated with a wave of 166- cycles, and the modulation wave will be passed by the ?lter I66 to energize the magnet I69 and close the armature 12 on the contact 116, there- by completing a circuit from a battery 14 through a solenoid I15. The solenoid thereupon attracts its plunger I16, causing a pawl I11, connected to the plunger, to be pulled into engagement with ratchet teeth I18 on a rudder wheel 19 and advance the wheel clockwise by the length of one of the ratchet teeth. A spring "186 normally maintains the pawl I 11 clear of- the teeth I18stationary cam face I81 guides the pawl into engagement with the ratchet teeth as it is moved by the plunger I16. The rudder wheel 19 is secured to a rudder - post 82 carrying a rudder 83, so that the rudder is moved a predetermined distance toward the left in response to a single actuation of the key at .the transmitting station. The key need be closed only momentarily, and as soon as it is released the magnet I69 and the solenoid I15 are released, whereupon the pawl I11 and plunger 116 are retracted into neutral position by the spring 186. If the key at the transmitting station is. actuated, then the carrier wave is modulated with the BOO?cycle modulating wave, which is passed by the ?lter 566 at the receiving station, to en- ergize the magnet 569. ture 12 on the contact 516, to energize a solenoid 515, identical with the solenoid I15, and actuate a pawl 511 Which engages with ratchet teeth 518. The latter are oppositely directed with. respect to the ratchet teeth I18, so that the pawl 511 and the teeth 516 function to shift the rudder 63 to the right, instead of to the left. Some means must be provided?to retain the rudder 63 in whatever position it has been moved by the pawl I11 or 511, and we have shown a brakedrum 84' frictionally engaged by a brake- band 85 and connected by a pinion 86 and a gear segment 81 to the rudder wheel '19. band 85 offers suf?cient frictional resistance to movement of the rudder to retain it in the posi- tion to which it has been moved, but insuf?cient to prevent movement of the rudder by the pawls I11 and 511. The tuning condensers 24? to inclusive, at the receiving station are adapted to be cont This closes the armaThe brake 70 75 3 nected one at a time to the selector totune it to different frequencies, by contacts similar to the contacts 3 at the transmitting station, and actuated in the same way under the control of a record strip 31', which may be identical with the record strip 31 at the transmitting station, and is pulled over a control head 39? by a clock motor 41' which runs at the same speed as the motor 4 at the transmitting station. The de- tailsof the control head 39' and the switches Whereby the latter are closed in response to dif- ferently positioned perforations in the record strip 31', are the same as those at the transmit? ting station, which were described with reference to Figscourse necessary that the record strips 31 and 31' at the transmitting and receiving sta- tions, respectively, be started at the same time and in proper phase relation with each other, so that corresponding perforations in the two record strips will move over their associated control heads at the same time. We therefore provide an apparatus for holding both record strips in a starting position until the torpedo is ?red, and for then simultaneously releasing both strips so that they can be moved at the same speed by their associated motors 4 and The holding mechanism at each station in- cludes a pin I66 (Fig. 6) slidably mounted for vertical movement 1n the head 45 and adapted to engage a special starting hole I61 (Fig. 4) in its associated record strip. The pin I66 is normally urged into a lower position by a compression spring I62, as shown in Fig. 5, so that it is clear of the record strip and does not impede its move- ment. However, the pin is adapted to be held in upper position in engagement with the hole I61 in the record strip, by a solenoid I63 having a plunger I64 which is connected to the pin I 66. The solenoid is shown energized in Fig. 6. Referring now to Fig. 3, when a torpedo equipped with the apparatus disclosed in Fig. 2 is prepared for ?ring from the mother Ship, on which the transmitting apparatus of Fig. 1 is mounted, both the solenoid I63 on the torpedo and the solenoid 163 in the transmitting?equip- .ment, are connected in series with a battery I65 by a circuit including conductors I66 which ex- tend between the torpedo and the transmitting station on the mother ship, thereby holdingboth the record strips in starting position. When the torpedo is ?red, the conductors I66 are broken, thereby interrupting the series energizing cir- cuit of the solenoids I63 and releasing both sole- noids simultaneously to permit the strips at both stations to start in phase with each other. It will be noted that whereas there are seven tuning condensers 24 at the transmitting station, there are only four tuning condensers 24' at the receiving station. The extra three tuning con- densers at the transmitting station provide three additional channels for the transmitter for which there are no corresponding channels at the re- ceiver, to thereby permit the sending of false impulses to confuse the enemy. In the particular system shown, the receiving apparatus is effective to receive on the channels ineffective to receive on the channels A, B, and C. If the operator at the transmitting station sent a signal while the os- cillator was operating on one of the channels A, B, or C, the signal would not be received on the torpedo. It its therefore desirable to provide an indicator to advice the operator at the trans? mitting station when the transmitting and re- 4 ceiving stations: are both tuned :to the same fre- ?forations in the: row on therecord fstrip occur? I Lat the beginning, and; end of: each perforation in .10 the rrows D, E, andG, and extend between - . I successive, spaced, .perforationsin these, rows (at 3 which times perforations occur in cheer-more of . the rows 13;? and C. false; . . . . The. mechanism arranged as described, func-' . I Eeons/1:0 light thealamp 43: for a short time during- - i each transitionfrom one to another of the useful . channels D, E, F, and G, to warn, the operator; . i not-to transmit a control impulse at the moment- :of . transiticin; from one frequency? to another; The lamp 43, reinai?nsligihted throughout periods: - . i employed. . Various other? departures from: the exact isyStem' . described; will 5be apparent? to . Ski?e?? gay; is, therefore, to; be, the; appended claims; a, .i I 5 When'the tranSmitter :is: tuned? to. transmit in any: ;one of the channels A, 017.0. g'I?heoperator 1. fwill, of "Course, occasionally transmit: impulses; Nadine the transmitter: is tuned. to one of the;' -. B, ore, to 'misleadithe, enemy, hut: - [heswill know; by the factthatgthe lamp Allis. -, _v lighted, that these impulses rwill'notaifect: the- ._torpedo. titunderstood that: many :Variationsf i from the construction showncanbezmadewith- . out departing from .the? inventiOn,; Inns: in order; 511:7 to siniplify' the drawings a? record strip having 1 . only eight frows iota perforations fhas boon illus- - trated. 'However, as previously mentioned, sun-- her record strips employed in player: pianos: now 4 have as. many; as :88 rows - of perforations, and: a g40 similar number could 'be employed in the p?re's- ent system to provide a large number of useable channels, to which both the transmitting and receiving stations can be tuned, and also a large number of auxiliary channels at thetransmitter for sending false signals. If desired, the perforations corresponding to the false signals, may be omitted from the record strip at the receiver. However this is not neces- sary. The record strip at the transmitting and the receiving stations can be identical in all re- spects, and any number of rows of perforations in the record strip at the receiving station can be rendered ineffective by blocking the passages 48 in the receiving head that correspond to the - false channels. It will also be'obvious that the control heads 39 and 39' at the transmitting and receiving stations, respectively, can be iden- tical but the contact springs 54 and 58 (Fig. 6) at the receiver can be left disconnected in those channels in which false signals are transmitted. A very important feature of our system is that only relatively few and relatively short signals need be transmitted. Thus it is necessary only to close one of the keys I. or momentarily to de?ect the rudder 83 by one increment in either direction. The transmission. of a very short im- pulse may not be discovered by the enemy at all. Even if the enemy should pick up one of the impulses transmitted, he would not know whether it was an effective signal or a false sig- nal. Furthermore, it is quite possible to so ar- range the records that the receiver is never twice tuned to the same frequency. 2,292,337 . redescribing in edetallits application ito-theicon-W? . 3 1 _quo'ancy.E 'I?helamp 423., actuated by the 4 . switch 42 5(Elg. constitutes-such an; indicators The switch 42 is closed" to. light the lamp. 2. whenever an aperture inrrow-H: (Fig. 4) crime, . - record Strip moves overiits. associated passage as .in' the controlheadls. The; perforations in a; _rowH of the-record strip .areso; arrangedas to! light} the lamp .43. Whenever the; operator should not send a control signal- 2 To thisend. the pier? trolof altorpedoor. other craft where it is neces-: Esary to'steer' dimensidnfit Will beiiw; - to?those'skilled inithe arttha't byvuslng 4 i a: larger number Eof modulation i ?ditionail, sanctions can, be performed;- Thus by 3 1 using .four modulation anes having freQUencfes 'wof says mommies, and 'i . goon-cycles, respectively, and _usmgiapprOpriate 9 1 filtersat' the receiving: station, it isE obVicjusthat . *xtwo rudders Can. be Controlled. This Would be mdesirable when controlling aerial torpedoes or other types of oraft in which central in; a yer?j - 1 . tical direction; as? well. ass in 3.h0r120ntal.direc- ution, is desirable: :rhereils no'particular limit 3 - . 7 to the number of control: channels "that can be . 7 used with our i'nVention. - - It is also i of modulatiOn Ethan the Conventional one shown,- . ?20% 2'55 30: -, _LIna'secret. communication system, agtrans- ?9 1 clailns; is intended 3 the 'art?, . and the. invention including frequency? modulation Wave When - phase - limited only as Set forth a; claimr'w. mitt-mg station including? means for generating . . and "transmitting carrier waves of iaiplu'r'alityi of i 3 . a ?rst? elongated record, strip having i i differently characterized, longitudinally disposed . i . . recordings thereon, record-aetuat'GEd means selec'; 1 . i 3 tively responsive to different ones of said record? frequencies; lugs for determining the frequency of Said carrier 45 50 60 65 70 Although the invention has been explained by 75 waves. means, for moving Saidstrip ?pastisaia rec; 7 . 'OFd-astuated means whereby the carrier 'w'ave . . frequency is" changed from time to time in cordance with the recordings on said strip, a re? ceiving station including carrier wave?receiving means having tuning means tunable to said car- ner wave frequencies, a, second record strip, rec- ord-actuated means selectively responsive to dif- ferent recordings onrsaid second record strip for tuning said receiver to said predetermined carrier frequencies, and means for moving said second strip past its associated record?actuated means in with said ?rst strip, whereby the record-actuated means at the transmitting sta? tion and at the receiving station, respectively, are actuated in to maintain the receiver tuned to the carrier frequency of the transmitter. 2. Apparatus as described in claim 1, in which said di?erently characterized recordings on said record strips are distinguished by being differ- ently laterally displaced from each other, and said record-actuated means are selectively re- sponsive to the lateral positioning of said record- ?gs. 3. Apparatus as described in claim 1, in which said record strip comprises a ribbon having lon- gltudinally extending slots therein differently characterized by being differently laterally posi- tioned on said ribbon, and each said record-ac- tuated means includes a plurality of movable ele- ments each movable to tune its associated gener- ating or receiving means to a different one of said frequencies, and means for selectively moving said elements in accordance with the lateral po- sitioning of the slots in said ribbon. 4. In a system of the type described, including a control station and a movable craft to be con- to behnderstoodthat other methods a 5: .7 . . . or'Phasemedu- i: 3 . 18131011, Canbeemployediinour system. as3us?edin-thef73 91? jfrmuencrmodulation' is, . i 1 2,292,387 trolled thereby, apparatus at said control station comprising an oscillator and tuning means there- for, a ?rst elongated record strip having di?'er? ently characterized, longitudinally disposed re- cordings thereon, record-actuated means selec- tively responsive to different ones of said record- ings for tuning said oscillator to predetermined different frequencies, means for moving said rec- ord strip past said record-actuated means Where- by the frequency of oscillation is changed from time to time in accordance with the recordings on said strip, and means for selectively transmit- ting radio signals corresponding in frequency to the said frequency of oscillation; apparatus on said movable craft comprising a radio receiver having tuning means tunable to said predeter- mined frequencies, a second record strip, record- actuated means selectively responsive to different recordings on said second record strip for tuning said receiver to said predetermined frequencies, means for moving said second strip past its asso- ciated record-actuated means in with said ?rst strip whereby the record-actuated means at the control station and on the mov- able craft, respectively, are actuated nism to maintain said radio receiver tuned to the frequency of oscillation of the transmitter; mechanism on said craft for selectively deter? mining its movement, and means responsive to radio signals received by said radio receiver for controlling said mechanism. - 5. Apparatus as described in claim 4, in which said mechanism on said?craft for selectively de- termining its movement includes a control ele- ment movable by predetermined increments, and means responsive to successive received radio im- pulses for moving said element by one increment only in response to each separate impulse irre- spective of the length of the impulse. 6. Apparatus as described in claim 1, including means at the transmitting station for transmit- ting radio signals of di??erent frequencies to which said radio receiver tuning means are not tunable, and means coordinated with the record- ings on said ?rst strip for indicating at the trans- mitting station when the transmitting apparatus is tuned to frequencies that are not receivable at the receiving station. HEDY KIESLER MARKEY. GEORGE ANTHEIL.