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“SECRET COMMUNICATION SYSTEM”: FREQUENCY HOPPING; THE SOLUTION FOR THE JAMMING PROBLEM


HEDY LAMARR   Hedy Lamarr. She Born Hedwig Eva Maria Kiesler in Vienna, Austria-Hungary in 1914, Lamarr was first known for her risqué role in the 1933 Czech film Ecstasy. At 19 she married Friedrich Mandl, a munitions manufacturer with ties to Mussolini and Hitler. Mandl insisted she accompany him to meetings, often with scientists and others with military knowledge. Here she was exposed to applied science, a subject that interested her for many years. Lamarr developed a passion for helping the U.S. military after walking away from the unhappy marriage to the Austrian Fascist weapons manufacturer in 1937. [03] She made plans to leave both her husband and Europe and booked passage on a boat to the United States. Making the acquaintance of Louis B. Mayer along the way, she had an MGM contract before hitting land. Often cast as the exotic seductress, she starred opposite other greats including Spencer Tracy, Clark Gable, James Stewart, Lana Turner and Judy Garland. [01] Hedy Lamarr was a movie star in the golden age of Hollywood of the 1930s and 40s. George Antheil was a Dadaist avant garde composer. The two became friends, and during World War II, they became inventors. [02]Called the most beautiful woman in the world, Hedy Lamarr was a MGM actress in the golden era of Hollywood, but her real life story is better than any of her films. She may have also been a kleptomaniac, but she was anti-Nazi and concerned about the Allied forces in World War II. Hedy Lamarr wasn’t just a beautiful movie star. According to a new play, Frequency Hopping, she was also a shrewd inventor who devised a signal technology that millions of people use every day. [03] THE IDEA FOR A NEW PATENT It is the explain how one of the best known actresses of mid-20th century revolutionized weapons systems and helped create cell phones [03] Lamarr developed the idea of frequency hopping, a system of randomly creating a sequence of frequency changes understood by the controller and the torpedo to mask the signal. With Antheil’s help, they used a piano roll to randomly change between 88 frequencies (the number of keys on a keyboard) to encrypt the signal. A patent was granted to Lamarr (under her married name Markey) and Antheil for a “Secret Communication System” but the thought of controlling torpedoes with an electro-magnetic piano roll didn’t immediately appeal to the US Navy. Despite having a patent for Frequency Hopping technology, Charles Kettering suggested she would be more help to the war effort by using her celebrity to sell bonds, which she did. Still her invention is sited in later patents for spread-spectrum communication technology which is used for GPS, Wi-Fi and cell phones today. [01] In an attempt to stall her acting career, he had brought her to his business meetings, where she found herself continuously listening to “fat bastards argue antiaircraft this, vacuum tube that,” explains Lamarr’s character—played by Erica Newhouse—in the play, Frequency Hopping. In the meetings, they had talked about developing detection devices to listen to, and jam, the radio signals that American aircraft and weapons used to communicate with one another; and Lamarr wanted to foil their plans. “Can you guide your torpedo towards an enemy target—or just use radio control period—without being detected? Or jammed?” Lamarr’s character asks. [03] Spread spectrum technologies are useful in situations where a large number of radio communications are taking place near each other, such as in a cellphone system or a WiFi network. Techniques similar to Lamarr and Antheil’s system make it possible for many phone users or computers to use the same cell tower or wireless router at the same time without too much interference or loss of signal. [02] “SECRET COMMUNICATION SYSTEM” FREQUENCY HOPPING; THE SOLUTION FOR THE JAMMING PROBLEM In 1941 Lamarr met avant-guard composer George Antheil who experimented with player pianos and the automated control of musical instruments. Drawing on her previous military exposure, Lamarr realized torpedoes could be controlled by radio frequency to more accurately strike enemy ships, but the signal would be easily detected and jammed, rendering the torpedo useless. The actress and the composer wanted to find a way to securely guide torpedoes. While radio remote controls for torpedoes already existed, they had a major weakness: once the targeted ship figured out what frequency was being used by the attacking ship to guide the torpedo, they could jam the control signal by broadcasting noise on that frequency and overpowering the commands from the attacking ship. [02] In addition to being harder to block, messages broadcast on a frequency hopping system are also harder to intercept: if a would be eavesdropper is listening to one particular frequency, they will hear at most a short part of a message before the radios jump to a different frequency. [02] A key part of making this “Secret Communication System” work was coordinating the frequency shifts between the ship and the torpedo. The torpedo’s receiving antenna needs to be tuned to the same frequency as the ship’s broadcasting antenna in order to receive the guidance signal. [02] Lamarr’s solution to the jamming problem was to spread the control signal over a variety of frequencies. The control signal from the attacking ship would start out on one frequency, and then jump to another frequency, and then yet another. By changing frequencies at regular intervals, it would be much harder for the enemy to jam the control signal, since it would take a huge amount of power to block all the possible frequencies that the attacking ship was using. [02] Here, Antheil’s experience as an avant garde composer came in handy. He was obsessed with machinery, and in particular, once wrote a piece that was intended to feature sixteen player pianos. This provided a way to keep the two antennas in sync: the ship and the torpedo would each have an identical player piano roll. Rather than controlling a musical instrument, the marks on the rolls would set each antenna to a particular frequency. So, by reading the player piano rolls at the same speed, the ship and torpedo could keep jumping frequencies, and still have their antennas tuned together. [02] Lamarr and Antheil’s frequency hopping system was one of the first designs in a broader class of communications technologies called spread spectrum techniques. These technologies use a larger range of frequency bandwidth than is strictly necessary just to convey a message alone, like the Secret Communication System’s jumping around using a variety of frequencies. [02] Lamarr realized that by transmitting radio signals along rapidly changing, or “hopping,” frequencies, American radio-guided weapons would be far more resilient to detection and jamming. The sequence of frequencies would be known by both the transmitter and receiver ahead of time, but to the German detectors their message would seem like gibberish. “No jammer could detect it, no German code-breaker could decipher a completely random code,” she says in the play. [03] DELAY IN USE THE NEW TECHNOLOGY In 1940 after working on the project for several years, Lamarr called on an unlikely invention partner: avant-garde composer George Antheil, 13 years her senior. As the play—which includes a 25-piece robotic orchestra performing one of Antheil’s most renowned pieces—makes clear, frequency hopping spread spectrum is based on a musical concept. The frequencies are “carried in waves through space like melodies,” Lamarr’s character explains. [03] More broadly, frequency hopping can be compared with aspects of human communication, argues the production’s Brooklyn-based playwright and director Elyse Singer, whose other works include Love In The Void (alt.fan.c-love), a play about Courtney Love’s Internet postings. Just as the frequencies “hop” to avoid detection, “we send secret codes to each other, shift and hop and avoid, especially in romantic relationships,” Singer says. The play explores this theme in the tumultuous relationship that develops between Lamarr and Antheil. [03] The pair succeeded in patenting their technology, and presented the concept to the National Inventors Council in 1940, but their invention—which used a piano roll to change between 88 frequencies—was not well received. “The U.S. Navy said, ‘Thank you very much for the patent, Miss Lamarr—we won’t be needing your services here in Washington,'” Lamarr’s character laments onstage. [03] Unfortunately, the navy didn’t immediately use Lamarr and Antheil’s system. The basic idea was not used until 1962 during the Cuban Missle Crisis, and by then the patent had expired. , by this time of the Cuban Missile Crisis, frequency hopping radios were in common use on Navy ships, using electronic devices to keep frequencies synchronized rather than player piano rolls. [02]. The technology was little noticed until ITT (International Telephone and Telegraph) found it while doing patent research for the civilian coding system CDMA, and duly noted the expired work. This according to Lamarr supporters validates the claim that Frequency Hopping is the basis for spread-spectrum communication technology, used in Bluetooth, Wi-Fi network connections and CDMA (Code Division Multiple Access), a channel access method used in wireless phones. [01] The delay in use of a now common technology begs the question, are people with good ideas but lack the usual education and experience taken seriously? There are practical reasons why Lamarr’s idea was not immediately used. The military already had a lot on it’s plate, radar, sonar, the atomic bomb, and the components needed may have been too crude or not available at all in 1942. There are skeptics that feel Lamarr has received too much credit, or because of lax patenting practices may not have had a new or worthy idea at all. (See patent US 723188 A, N. Tesla, 1903) When you dig deeper and find stories of Lamarr and Antheil meeting over a breast augmentation discussion (Antheil being a self proclaimed expert in Glandular Criminology) or Lamarr’s simplistic responses when questioned about the invention it’s hard not to have doubts. While ITT sited the patent, it had no bearing on ITT’s development of CDMA and was more of a novel antidote to an otherwise dull document. She and Antheil were recognized with the 1997 Electronic Frontier Foundation Pioneer Award, but received little or no compensation in their lifetimes. Maybe Hedy Lamarr was ahead of her time. Maybe she was just passing on something she overheard in her Nazi-sympathizer ex-husband’s business meetings. Does she belong in a list of great inventors? I tend to think not and that her story is overly romanticized, but I do respect her as an intelligent person looking to solve a complex problem. Whatever you believe it makes a great Hollywood script. Hedy Lamarr died in Florida in 2000[01] The technology, says Singer, was far ahead of its time. Although her ideas were at first ignored, the technology (which she and Antheil patented in 1942) was later used by the military—during the Cuban missile crisis in October 1962, for example—and more recently, it has been employed in wireless technologies like cell phones. It was eventually recognized in 1997, when the Electronic Frontier Foundation honored Lamarr with a special Pioneer Award and she became the first woman to receive the Invention Convention‘s BULBIE Gnass Spirit of Achievement Award. [03] A performace fittingly, Frequency Hopping is itself a highly technological production Being able to project images on two planes helps us to get into Lamarr and Antheil’s mindscape, which is really where artists and scientists develop new ideas,”. Frequency Hopping was runs in 2008 at New York City’s 3LD Art & Technology Center.[03] [01] Hedy Lamarr and Frequency Hopping From : http://www.deadinventors.com/2013/10/hedy-lamarr-and-frequency-hopping.html [02] http://www.businessinsider.com/hedy-lamarr-george-antheil-frequency-hopping-2014-7 [03] Hedy Lamarr: Not just a pretty face by By Melinda Wenner on June 3, 2008. http://www.scientificamerican.com/article/hedy-lamarr-not-just-a-pr/ Rights & Permissions [04] performances through June 29  2008 at 3LD Art & Technology Center http://www.hourglassgroup.org/frequency.html [05] PDF: https://patentimages.storage.googleapis.com/pdfs/US2292387.pdf WEB: https://www.google.com/patents/US2292387?dq=hedy+lamarr+patent&hl=en&sa=X&ei=6OBUUqGrJrHwiQLJ4YDICA&ved=0CDcQ6AEwAA See also: https://en.wikipedia.org/wiki/Hedy_Lamarr It was lots more fun being scientific than going to the movies. – Hedy Lamarr quote from The Stars and Stripes [01] Source [01] Credit: Courtesy of Dixie Sheridan Written & Directed by Elyse Singer Original Score by Joshua Fried performed by the 25-piece automated Ballet Mécanique Orchestra Production and Multimedia Design by Elaine J. McCarthy Starring Erica Newhouse and Joseph Urla Costume Design by Angela M. Kahler Lighting Design by Tyler Micoleau Sound Design by Marcelo Anez Wigs and Make-up Design by J. Janas and R. Greene Robotics by Eric Singer’s LEMUR: League of Electronic Musical Urban Robots Programmed by Paul Lehrman/Ballet Mécanique Project Dramaturg: Erika Rundle [04] PATENT [05] Secret communication system US 2292387 A Source : Google H. K. MARKEY ETAL, SECRET COMMUNICATION SYSTEM Filed June 10, 1941 2,292,387 2 Sheets-Sheet 1 Patented Aug. 11, 1942 H. K. MARKEY ETAL, SECRET COMMUNICATION SYSTEM Filed June 10, 1941 2,292,387 2 Sheets-Sheet 2 Patented Aug. 11, 1942

Publication number US2292387 A
Publication type Grant
Publication date Aug 11, 1942
Filing date Jun 10, 1941
Priority date Jun 10, 1941
Inventors Antheil George, Markey Hedy Kiesler
Original Assignee Antheil George, Markey Hedy Kiesler
Export Citation BiBTeX, EndNote, RefMan

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 6 Claims. (CI. 250-2) This invention relates broadly to secret communication systems involving the use of carrier waves of different 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 relatively simple and reliable in operation, but at the same time is difficult to discover or decipher. Briefly, our system as adapted for radio control of a. remote craft, employs a pair of synchronous 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 determine 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 positioned in a. plurality of longitudinal rows along the records. In a conventional player piano record there may be 88 rows of perforations, and in our system such a record would permit the use of 88 different carrier frequencies, from one to another of which both the transmitting and receiving station would be changed at intervals. Furthermore, records of the type described can be made of substantial length and may be driven slow or fast. This makes it possible for a. pair of records, one at the transmitting 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 synchronized by driving 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 periodically correct the position of the record at the receiving station by transmitting synchronous impulses from the transmitting station. The use of synchronizing impulses for correcting the phase relation of rotary apparatus at a receiving station is Well-known and highly developed in the fields of automatic telegraphy and television. Other more specific objects and features of our invention will appear from the following detailed description of a particular embodiment thereof, as illustrated in the drawings, in which Fig. 1 is a schematic diagram of the apparatus at a transmitting station; Fig. 2 is a schematic diagram of the apparatus at a receiving station; Fig. 3 is a schematic diagram illustrating a starting circuit for starting the ,motors at the transmitting and receiving stations simultaneously; 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 record-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 VI-VI of Fig. 5, but showing the record strip in a different longitudinal position; and Fig. 7 is a diagram in plan illustrating how the course of a torpedo may be changed in accordance with the invention. Referring first to Fig. 7, there is disclosed a mother ship 10 which at the beginning of operations occupies the position la and at the end of the operations occupies the position l0b. This mother ship discharges a. torpedo II that travels successively along different paths l2, l3, I4, l5 and IE to strike an enemy ship 17, which initially’ occupies the position 17c but which has moved into the position llb at the time it is struck by the torpedo H. According to its original course, the enemy ship I! would have reached the position I10, but it changed its course following the firing 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 circumstances, be observed directly from the mother ship 10a, or its course may be followed by an observer in an airplane l8 who communicates his findings to the mother ship Illa. It is also possible to control the torpedo directly from the airplane IB if the latter is equipped with the necessary synchronous transmitting equipment in accordance with the invention. Under the particular circumstances of Fig. 7, the enemy ship 17 was traveling in a straight line substantially parallel to the mother ship 17 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 17 and for water currents represented by the small arrows 19. However, as a result of the change in course of the enemy ship 17 and the effect of the water currents, it is observed that 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 12 and follow the path B. At later times it is noted that further changes are necessary, and its course is successively changed from the path l3 to the path l4, to the path i5, and to the path ii, in order to strike the enemy ship l7b. The remote control of the torpedo as described is old and broadly does not constitute a part of our invention. However, it has been very difficult in the past to employ radio control of a torpedo, for the reason that the enemy could quickly discover the frequency of the control signals 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 receivers for the remote control, and change the frequency at intervals by synchronous records at the two stations. Referring to Fig. 1, the apparatus at the transmitting station includes as its main elements a variable-frequency carrier oscillator 20, a modulator 2|, an amplifier 22, and an antenna 23. These elements are represented schematically since their exact construction does not constitute a part of the present invention. Suffice it to say that the variable-frequency. carrier oscillator 2|! is controlled to oscillate at different frequencies by a plurality of tuning condensers 24a, 24b, 24c, 24d, 24c, 24!, and 24a, adapted to be independently connected to the oscillator by automatically controlled switches 3|, one for each condenser. The different condensers 24a to 2417, inclusive, are of different capacities, and these differences are indicated in the drawings by different spacing’s between the plates. Two controls are provided in the system of Fig. 1, in the form of two keys L and R, respectively. Key L is employed to transmit a signal for applying left rudder to the distant torpedo, and the key R is employed to apply right rudder to the torpedo. Actuation of the key L closes main contacts 32, which connect the output of the oscillator 20 to the modulator 21, and at the same time closes contacts 33, which connect a 100-cycle oscillator 34 to the modulator 21, which there upon modulates the particular carrier wave being generated at that time by the oscillator 20. The modulated carrier wave is then amplified in the amplifier 22 and transmitted from the antenna 23. If the operator desires to app y 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 oscillator 36 to the modulator 21. The switches 31 are selectively closed by a record-controlled mechanism actuated by a record strip 31, which is drawn off a supply roll 36 over a control head 39 and wound up on a take up spool 40 driven by a constant-speed clock motor 41. Referring now to Fig. 4, the record strip 27 has perforations arranged in eight different longitudinally extending rows A, B, C, D, E, F, G, and H, respectively. Perforations in the rows A, B, C, D, E, F, and G control the seven switches 3| associated with the different tuning condensers 24a to 24g, inclusive. The perforations in row H control an auxiliary switch 42 (Fig. 1), which lights a signal lamp 43 from a battery 44. The strip 37 is drawn over the control head 39, as a previously mentioned and the control head responds to perforations in the different rows A to H, inclusive, on the strip, to close the various switches 31 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 45 over which the record strip is drawn and which has a plurality of vertical passages 46, the orifices of which are juxtaposed to the different rows A to H, inclusive, of the strip. In Fig. 5 two of the passages 46 are shown juxtaposed to and in communication with apertures in the two rows C and G 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 suction pump 56. Each of the passages 46 is also connected by a tube 61 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 3|. The movable spring 54 is separated by a block of insulation 55 from the lower end of its associated piston 63. The pistons are normally maintained in upper position in which shoulders 66 thereon lie against the lower face of the cylinder block 51 containing the cylinders 62, under which conditions the contacts 31 are open. However, under certain conditions to be described, the pistons 53 are urged downwardly, by compression springs 53a positioned there above, to carry the movable springs 64 against the cooperating contact springs 58 to close the switches 37. The pistons 53 are maintained in uppermost position, in which the switches 37 are open, when a solid portion of the record strip 31 overlies the passages 46, but are depressed by the springs 53:: when apertures in the record strip move into registration with the passages 6. Thus so long as the upper end of a passage 46 is closed by the record strip 31, suction is up plied from the manifold 48 through the restrict ed passage 41 to the cylinder 62, and lifts the piston 53 against the force of the spring 63a. However, when a perforation in the record strip is in registration with a passage 46, air flows freely info 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 63a to move the piston downwardly and close the associated switch 31. It will be obvious that by so positioning the perforations in the different rows A, B, C, D, E, F, and G, 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 condensers 24a to 24g (Fig. 1) inclusive, to the oscillator 26 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 torpedo 11 of Fig. 1), comprises a receiving antenna 60 and a signal selector 61 that may be tuned to any one of four different frequencies by connecting thereto different condensers 24’d, 24’e, 24’f, and 24’g. When the condenser 24’d is connected to the selector 61 and the condenser 24d is connected to the oscillatr 20, the transmitter and receiver are both tuned to the same frequency, and so on. When a signal received on the antenna 60 is of the same frequency to which the selector 61 is tuned, the signal is amplified in an amplifier 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 filters I66 and 566, the first of which is tuned to l00-cycles and the second to 500-cycles. The output of the filter I66 is delivered through a rectifier I68 to a magnet I69, and the output of the filter 566 is delivered through a rectifier 568 to a magnet 569. The magnets I69 and 569 act on a common armature 12, which is normally positioned in a neutral position but moves in response to energization of magnet I69 to close on a contact I and moves in response to energizaticn of magnet 569 to close on a contact 510. If a received signal was produced by actuation of the key L (Fig. 1) at the transmitting station, then it is modulated with a wave of 100- cycles, and the modulation wave will be passed by the filter 166 to energize the magnet I69 and close the armature 72 on the contact 170, thereby completing a circuit from a battery 14 through a solenoid I15. The solenoid thereupon attracts its plunger 176, causing a pawl 177 , connected to the plunger, to be pulled into engagement with ratchet tecth 178 on a ruder whell 79 and advance the wheel clockwise by the length of one of the ratchet teeth. A spring 180 normally maintains the pawl 177 clear of the teeth 178, and a stationary cam face 181 guides the pawl into engagement with the ratchet teeth as it is moved by the plunger 176. The rudder wheel 79 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 L. at .the transmitting station. The key need be closed only momentarily, and as soon as it is released the magnet I69 and the solenoid I are released, whereupon the pawl 177 and plunger 176 are retracted into neutral position by the spring 180. If the key R at the transmitting station is actuated, then the carrier wave is modulated with the 500-cycle modulating wave, which is passed by the filter 566 at the receiving station, to energize the magnet 569. This closes the armature 72 on the contact 570, to energize a solenoid 575, identical with the solenoid I15, and actuate a pawl 577 which engages with ratchet teeth 578. The latter are oppositely directed with respect to the ratchet teeth 178, so that the pawl 577 and the teeth 578 function to shift the rudder 83 to the right, instead of to the left. Some means must be provided to retain the rudder 83 in whatever position it has been moved by the pawl 177 or 511, and we have shown a brakedrum 84 frictionally engaged by a brakeband 85 and connected by a pinion 86 and a gear segment 81 to the rudder wheel 79. The brake band 85 offers sufficient frictional resistance to movement of the rudder to retain it in the position to which it has been moved, but insufficient to prevent movement of the rudder by the pawls 177 and 577. The tuning condensers 24’d to 24’g, inclusive, at the receiving station are adapted to be connected one at a time to the selector 6|, to tune it to different frequencies, by contacts 3I’ similar to the contacts 3I 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 M which runs at the same speed as the motor M at the transmitting station. The details of the control head 39′ and the switches 31, whereby the latter are closed in response to differently positioned perforations in the record strip 31′, are the same as those at the transmitting station, which were described with reference to Figs. 5 and 6. It is of course necessary that the record strips 31 and 31′ at the transmitting and receiving stations, 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 fired, and for then simultaneously releasing both strips so that they can be moved at the same speed by their associated motors M and M The holding mechanism at each station includes a pin 100 (Fig. 6) slidably mounted for vertical movement in the head 45 and adapted to engage a special starting hole 101 (Fig. 4) in its associated record strip. The pin 100 is normally urged into a lower position by a compression spring 102, as shown in Fig. 5, so that it is clear of the record strip and does not impede its movement. However, the pin is adapted to be held in upper position in engagement with the hole IOI in the record strip, by a solenoid 103 having a plunger 104 which is connected to the pin 100. 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 firing from the mother ship, on which the transmitting apparatus of Fig. 1 is mounted, both the solenoid 103 on the torpedo and the solenoid 103 in the transmitting’ equipment, are connected in series with a battery 105 by a circuit including conductors 106 which extend between the torpedo and the transmitting station on the mother ship, thereby holding both the record strips in starting position. When the torpedo is fired, the conductors 106 are broken, thereby interrupting the series energizing circuit of the solenoids 103 and releasing both solenoids 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 condensers at the transmitting station provide three additional channels for the transmitter for which there are no corresponding channels at the receiver, 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 D, E, F, and G, but is ineffective to receive on the channels A, B, and C. If the operator at the transmitting station sent a signal while the oscillator 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 transmitting station when the transmitting and receiving stations are both tuned to the same frequency. The lamp 43, actuated by the auxiliary switch 42 (Fig. 1) constitutes such an indicator. The switch 42 is closed to light’ the lamp 43 whenever an aperture in row H (Fig. 4) ,of’ the, record strip moves over its associated passage 4 row of the record strip are so arranged as to light’ the lam’p43 whenever the operator should not send a control, signal- To this end, the perforations in the row Hon the record strip occur at the beginning and: end of: each perforation in I the rows D, Eli, and G, and extend between successive, spaced, perforations in these rows (at which times perforations occur in one or more of the rows, A, B, and C, which transmit false signals). The, mechanism arranged as described, functions to light the lamp 43 for a short time during each transition from one to another of the useful channels D,E, F, and C. The operator will, of course, occasionally transmit impulses while the transmitter is tuned to one of the channels A,B, or C to mislead the enemy but he will know, by the fact the lamp 43 is lighted, that these impulses will not affect the torpedo. It will be understood that many variations, from the construction shown can be made without departing from the invention- Thus in order to simplify the drawings a record strip having only eight :rows of perforations has been illustrated. However, as previously mentioned, similar record strips employed in player pianos now have a many has as :88 rows of perforations, and a similar number could be employed in the present 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 the transmitter 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 necessary. The record strip at the transmitting and the receiving stations can be identical in all respects, and any number of rows of perforations in the record strip at the receiving station can be rendered ineffective by blocking the passages 46 in the receiving head that correspond to the false channels. It will also beobvious that the control heads 39 and 39′ at the transmitting and receiving stations, respectively, can be identical but the contact springs 54 and 5! (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 L or R momentarily to deflect the rudder 83 by one increment in either direction. The transmission of a very short impulse 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 signal. Furthermore, it is quite possible to so arrange the records that the receiver is never twice tuned to the same frequency. Although the invention has been explained by describing in detail its application to the control of a torpedo or other craft where it is necessary to steer in only one dimension, it will be I obvious to those skilled in the art that by using I a large number of modulation frequencies, additional functions can be performed. Thus by 1 using four modulation waves having frequencies “of say 100-cycles, 500-cycles, 1000-cycles and 2,000-cycles, respectively, and using appropriate filters at the receiving station, it is obvious that I two rudders can be controlled. This would be I recordings thereon, desirable when controlling aerial torpedoes or other types of craft in which control in, a vertical’ direction, as well as in a horizontal direction, is desirable. There is no particular limit to the number of control channels that can be used with our invention. It is also to be understood that other methods of modulation than the conventional one shown, including frequency modulation or phase modulation, can be employed in our system. The expression “carrier wave,” as used in the claims, is intended; to define the unmodulated wave when phase or frequency modulation is including frequency; modulation or phase modulation is employed. Various others departures from the exact system described will be apparent to those skilled’ in the art, and the invention’ is, therefore, to: be limited only a set forth in the appended claims. We claim: 1. In a secret communication system, a’transmittingstationincluding means for generating, and transmitting carrier waves of a’plura’lity of i I I frequencies, a first elongated record strip having I 1 differently characterized, longitudinally disposed record-actuatedmeans selec 1 tively responsive to different ones of said record’- I 1 ings for determining the frequency of said carrier Although the invention has been explained by I vl’raves, mean for ord-actuated means whereby the carrier wave frequency is changed from time to time in ac cordance with the recordings on said strip, a receiving station including carrier wave-receiving means having tuning means tunable to said carner wave frequencies, a second record strip, record-actuated means selectively responsive to different recordings on’said second record strip for tumn said receiver to said predetermined carrier frequencies, and means for moving said second strip past its associated record-actuated means in synchronism with said first strip, whereby the record-actuated means at the transmitting station and at the receiving station, respectively, are actuated in synchronism to maintain the receiver tuned to the carrier frequency of the transmitter. 2. Apparatus as described in claim 1, in which said differently characterized recordings on said record strips are distinguished by being difierently laterally displaced from each other, and said record-actuated means are selectively reisponsive to the lateral positioning of said record- 3. Apparatus as described in claim 1, in which said record strip comprises a ribbon having longitudinally extending slots therein differently characterized by bein differently laterally positioned on said ribbon, and each said record-actuated means includes a plurality of movable elements each movable to tune its associated generating or receiving means to a different one of said frequencies, and means for selectively moving said elements in accordance with the lateral positioning of the slots in said ribbon. 4. In a system of the type described, including a control station and a movable craft to be controlled thereby , apparatus at said control station comprising an oscillator and tuning means therefor, a first elongated record strip having differently characterized, longitudinally disposed recordings thereon, record-actuated means selectively responsive to different ones of said recordings for tuning said oscillator to predetermined different frequencies, means for moving said record strip past said record-actuated means whereby the frequency of oscillation is changed from time to time in accordance with the recordings on said strip, and means for selectively transmitting 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 predetermined frequencies, a second record strip, recordactuated 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 associated record-actuated means in synchronism with said first strip whereby the record-actuated means at the control station and On the movable craft, respectively, are actuated in synchronism to maintain said radio receiver tuned to the frequency of oscillation of the transmitter; mechanism on said craft for selectively determining 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 saidcraft for selectively determining its movement includes a control element movable by predetermined increments, and means responsive to successive received radio impulses for moving said element by one increment only in response to each separate impulse irrespective of the length of the impulse. 6. Apparatus as described in claim 1, including means at the transmitting station for transmitting radio signals of different frequencies to which said radio receiver tunin means are not tunable, and means coordinated with the recordings on said first strip for indicating at the transmitting station when the transmitting apparatus is tuned to frequencies that are not receivable at the receiving station. HEDY KIESLER MARKEY. GEORGE ANTHEIL.

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