Hedy Lamarr: inventor?
click on a picture to enlarge it and see its title
This is Hedy Lamarr.
This is Thomas Edison.
What do they have in common?
THEY WERE BOTH INVENTORS!
History popularizer Richard Rhodes devoted a book to exploring Hedy’s most renowned excursion into what we normally think of as Edison’s bailiwick. It’s called Hedy’s Folly. The author makes no attempt at objectivity but portrays his subject exactly as she would have wanted to be portrayed. Following a lead established by other writers, he sets out to convince us that “Hedy in Vienna, George [Antheil] in Paris and then the two of them meeting up in Hollywood to invent a fundamental new wireless technology makes a remarkable story …” Now neither Hedy nor her collaborator had had any training in wireless technology nor even in science, yet the breakthrough attributed to them – which goes under the name “frequency hopping spread spectrum” – is currently used in military and radio control applications and in consumer products that go under the name “bluetooth”; and its purview is sometimes extended by Hedy’s fans to encompass the entire realm of cell phones and WiFi.
So, take that, Edison!
From the looks of your fellow inventor, you didn’t need to expend all that perspiration after all.
On the other hand…
if you’ve been led to conclude as I have that the judgment of history is always wrong, you’ll be inclined to take a step back, ask who Hedy Lamarr was, what she knew, and what exactly she did contribute to the development of wireless technology.
She was born Hedwig Kiesler in Vienna in 1914 and left school at the age of 16 to follow a career in acting, landing small parts on the stage before going to Berlin to become involved in films. She muddled along with modest success until she attained instant fame by appearing naked in some of the scenes of a 1933 Czech film called Ecstasy.
The manner by which she achieved her renown – which her parents learned of only after the movie came out – would cling to Hedy and color people’s perception of her for the rest of her life. It was of course her attractiveness that led to her being invited to do nude scenes, and that same quality naturally drew the interest of the men she encountered. One of them was an Austrian industrialist and munitions manufacturer named Friedrich Mandl who persuaded her to marry him later in the same year that Ecstasy was released – also, by the way, the year in which Hitler came to power in Germany. After the marriage Mandl tried in vain to buy up all the copies of Ecstasy in order to have them destroyed. Hedy meanwhile found herself in charge of a household frequented by some of Austria’s richest and most influential men. It was a situation that would have delighted most women of ambition, of which Hedy was certainly one, but in this as in many other matters she proved to be quite different from most women. In fact she developed a distaste for her husband and the life into which he’d led her, resulting in a divorce after four years of marriage. Even before it took effect though, Hedy was off to Paris and then to London where she encountered U.S. film mogul Louis B. Mayer. He knew of her from her appearance in Ecstasy and invited the strikingly beautiful 22 year old to come to Hollywood. She arrived in October of 1937 and was awarded a boffo part in the movie, Algiers, with Charles Boyer. Over the course of the next dozen years she appeared in 19 films opposite such major stars as Clark Gable, Spencer Tracy, John Garfield, Robert Taylor and Jimmy Stewart,
Hedy capped her movie career in 1949 with her most commercially successful role, playing Delilah to Victor Mature’s Samson in Demille’s version of the biblical epic. But whatever positive qualities Hedy had were undermined by her penchant for making bad decisions. In her personal life this led to a string of sexual adventures and failed marriages; in her professional life to an attempt to transcend the crowd-pleasing popularity she’d achieved with her natural attractiveness by exercising greater control over the movies she became involved in. As things turned out, her success as Delilah was followed by a series of box office disappointments that gradually undid the degree of stardom she’d attained; and in contrast with actresses who managed to bounce back from temporary lulls, Hedy was never able to regain her former prominence. Few interesting roles came her way after 1951, and by the time her sixth and last marriage ended in 1965 her career had been in the doldrums for a long time.
She made headlines the following year by being arrested for shoplifting. The charge was dropped, but with the help of a couple of ghost writers she capitalized on her time in the spotlight by turning out an autobiography called Ecstasy and Me. In it she came across as self-absorbed, self-indulgent and sex-obsessed, and although she’d approved the contents of the book before it was released, she turned around afterward and disavowed everything in it, suing her publisher in the process. In fact she did relate many of its incidents quite differently on other occasions. In 1991 she was again charged with shoplifting and again let go. She lived out her life in relative seclusion, succumbing to heart disease at her home near Orlando, Florida in 2000 at the age of 85. Her later years bring to mind the travails of some other female stars of her era: Betty Hutton, for example, Veronica Lake and Rita Hayworth.
Enigmatic as Hedy was, one of the most intriguing things about her was that during the period of her maximum allure, she devoted a lot of her spare time to inventing things. A scientific lightweight she may have been, but the ideas she came up with depended on curiosity and imagination rather than technical competence. At one time or another she delved into such diverse realms as reconstituting soda pop from a pellet (a la Alka Seltzer), better designs for traffic signals and tissue boxes, and methods for tightening the skin. The idea for which she was awarded a patent, however, and whose subsequent revelation led to a curious renewal of fame in the 1990’s, lay in a field for which people of her background seem particularly ill suited. It was to making the weapons of war more deadly that Hedy and her musically inclined collaborator set their hands at the end of 1940.
Hedy had been in Hollywood for three years. Although the United States stayed on the sidelines when Germany invaded Poland in 1939, Hedy’s emotions became engaged with the plight of the Allies and especially the vulnerability of their ships to German U-boats. Given the fact that torpedoes were the primary means by which the Germans were sinking Allied ships, it’s curious that Hedy sought to improve the effectiveness of those devices rather than of measures designed to counteract them.
From 1933 to 1937 Hedy had been married to a munitions manufacturer, so she’d had contact with people familiar with military matters in general and submarine warfare in particular. She later recalled a conversation she’d had in 1936 with a German engineer involved in designing torpedoes that could be steered remotely after launch. Since torpedoes run under water, radio wasn’t a suitable means of guidance; a wire that unreeled from them during transit was the method most commonly employed. Glide bombs were a form of torpedo dropped from airplanes. They’d been introduced by Germany in World War I, and since they traveled through air they could be and were adapted to radio control during World War II. In seeking a patent, Hedy constructed a scenario in which torpedoes were launched from a ship and directed to their targets by a shipboard controller who could turn the torpedo’s rudder left or right with radio signals. Since radio didn’t propagate through water we’re led to wonder if Hedy intended the torpedoes to stay on the surface. Whatever she had in mind, the patent application made it clear that the recommended measures could be used to enhance the security of any device controllable by radio, whether on land, sea or in the air.
The deficiency of radio for wartime purposes to which Hedy addressed her attention was its vulnerability to interception and jamming. The solution she came up with was to vary the transmitted frequency in a pattern that would be unpredictable to an enemy. A commercially available radio of the time may have suggested the idea by allowing any of eight preset frequencies to be selected or changed from a dial on a remote control device.
The use of radio to guide devices from a distance had been invented and explored by others, so Hedy couldn’t hope to patent that part of her plan, but for any application in which radio control was appropriate, varying the frequencies in the way she described would make interception difficult or impossible. Therefore when she submitted a request to the patent office it was under the title, “Secret Communication System”. You can’t patent an electric light by noting that sending electricity through a wire will make it glow; and you can’t patent a secret communications system by noting that varying the frequency it uses will prevent jamming. You have to provide an application of your idea that’s capable of accomplishing a purpose you describe. That’s what Hedy set out to do by showing how her anti-jamming strategy could be used to make the remote control of torpedoes more secure. One of the things her idea relied on was that the sending and receiving radios always had to be tuned to the same frequency. A method for achieving that coordination was supplied by a man Hedy met almost by chance and who came to be listed as her collaborator.
His name was George Antheil (ANT-hile) and he was a composer.
Fourteen years Hedy’s senior, he’d been born in the United States, but his immigrant parents had raised him to speak German as well as he spoke English. He spent his childhood immersed in music to the virtual exclusion of other subjects, and by the age of 22 he’d become sufficiently accomplished as a pianist and composer to set his sights on joining the avant garde in Paris. He succeeded to the extent that he soon found himself among such cutting edge composers as Stravinsky, Satie, Milhaud and Auric. It was a time when outrageousness could be made to substitute for musicality in getting the public’s attention. George was invited to play some of his more outré piano pieces at the opening of the Swedish Ballet in Paris in 1923. One of the concert’s backers arranged for George’s performance to trigger a riot of the sort that had brought fame to Stravinsky’s Rite of Spring ten years earlier. George hadn’t been informed of what was going to happen, but he was unfazed by the furor he caused and even amused by it. And why not? Three years later he was able to capitalize on what he’d gone through to achieve the peak of his fame by staging a performance of his own Ballet Mecanique.
George’s score called for a variety of noise makers – saws, hammers, bells, and airplane propellers – along with conventional instruments and 16 synchronized player pianos. As things turned out, he was forced to cut the number of pianos to eight and have them played conventionally; but that proved adequate for his purposes. At its premiere in Paris Ballet Mecanique created a stir of just the sort George had hoped for, although it did fall short when he tried it again in New York. In researching the orchestration he’d intended to use, George spent a lot of time at the Pleyel piano factory learning about player pianos and how they worked – knowledge he was subsequently able to draw on in designing a device to implement a new approach to musical notation he’d come up with, in which a moving scroll guided a pianist’s fingers to the appropriate keys. He called the invention SEE-note and attempted to have it patented, but his efforts came to nothing.
George continued to knock about Europe for another half dozen years before moving back to the United States during the depths of the Depression. Outrageousness no longer offered a route to fame, and George’s musical innovations drew little interest. When an opera he’d labored over flopped at Julliard, he lapsed into a period of inactivity. His need for income eventually drove him to look for work in Hollywood. He arrived in 1936 and over a period of years was able establish himself as a writer of movie music – conventional by his earlier standards but suited to its purpose. By the time he met Hedy in August of 1940, he’d completed scores for the Demille films, The Plainsman and The Buccaneer. In spite of those successes, demands for his talents remained sparse.
Hedy and George were introduced at the home of a mutual friend. They found they had a lot in common. Like George, Hedy was an accomplished pianist, familiar with life in Europe and in Paris in particular. She spoke German and English, had a strong sympathy for England in its struggle against Germany, and was possessed of a curiosity that was wide-ranging but unschooled. It also happened to be the case that although George was married, he never passed up an opportunity to be around attractive women. From the similarity of their interests and perhaps for reasons more personal, Hedy and George wound up spending a lot of time together; and the concern they shared about the war in Europe led them to devote some of that time to exploring Hedy’s ideas for weapons improvements.
George’s attempts to get SEE-note patented had given him experience that proved relevant. His technical background was slight, but if there was one thing he knew something about, it was how a player piano worked. What it did was convert perforations cut in a paper scroll into the notes the piano played. The scroll was wide enough to accommodate 88 positions across, one for each of the piano’s keys. As the scroll was pulled over a horizontal bar with 88 openings, a vacuum in the bar allowed each perforation to be sensed by the flow of air it induced when it lined up with an opening. That flow was used to trigger a hammer into striking the key corresponding to the perforation’s position. If a player piano could be made to translate perforations into audio frequencies, a similar machine could surely be designed to translate perforations into radio frequencies. In the former a flow of air would cause a hammer to strike a particular key, in the latter it would cause a switch to enable a particular condenser.
In preparing to stage his Ballet Mecanique George had not only learned how a player piano worked but how to synchronize one piano with another. If each was equipped with an identically perforated roll that was put in motion at the same moment and kept moving by motors of the same speed, the two pianos would continue to play the same notes at the same time. While a piano roll had to accommodate 88 different notes, a secret communication system didn’t need anywhere near that number of frequencies. The example described in Hedy’s plan was limited to four frequencies for actually conveying information to the torpedo and three others to confuse a potential interceptor. What was needed then, was a paper ribbon wide enough to accommodate seven perforations – more like a teletype tape than a piano roll. One ribbon would control the frequency of the sending radio while an identically punched one would control that of the receiver. If both were set in motion by the launching of the torpedo, and they were advanced by motors of the same speed, the frequencies of sending and receiving radios would remain in sync. It all sounded plausible, but George never invested the effort it would take to build a prototype and put his design to a test.
There were additional details to be taken care of. A patent agent employed by the inventors located an electrical engineer to provide broad-brush schematics of the sending and receiving radios, with a separate condenser shown for each of the transmitter’s seven frequencies and each of the receiver’s four. The legal firm of Lyon and Lyon supplied patent attorneys to get the application into the proper form and make sure it presented each of its claims with the right level of detail. The proposal was submitted to the U.S. patent office on June 10, 1941 at the same time it was making its way to the War Department under the auspices of the National Inventor’s Council – with a push from some of George and Hedy’s high-placed friends. It wasn’t until early 1942, two months after the attack on Pearl Harbor, that the inventors heard anything back. The Navy had taken a look at their plan but rejected it. Hardly surprising under the circumstances. With the nation suddenly finding itself at war, investigating novel weapons designs wouldn’t have been high on the War Department’s list of priorities. Plus which the Navy didn’t use radio controlled torpedoes or have any plans for developing them, and the improvements known to be needed for their torpedoes were of an entirely different nature.
And, let’s face it, George’s contribution was a liability rather than an asset. The vacuum-based sensors used in player pianos were adequate for a bulky item that stood on the floor of a living room, but they’d been developed in the course of the preceding century in which electricity wasn’t available in the home, so they relied on foot pedals for the required power and currents of air rather than electricity to transfer forces. When multiple frequency radio was being expanded by other developers later on, the few who’d been made aware of George’s scheme were never tempted to use it.
Nevertheless there was some good news for the inventors. Six months after the Navy turned their proposal down, it was assigned patent number 2,292,387. Relying on different criteria from those of military evaluators, the people at the patent office concluded that the concept was original enough to get their blessing and the proposed application plausible enough. And that was all they insisted on. The award provided Hedy and George intellectual vindication, but no material rewards. Their proposal continued to lie in the Navy’s files, unused by the one customer at whom it had been aimed. The patent expired in 1959, the year that George died of a heart attack and long after Hedy had gone on to other things.
That then was the sum total of Hedy Lamarr’s contribution to wireless technology: she applied for and was given a patent for a method of protecting radio transmissions against jamming and interception by varying the frequencies-used in a manner that was unpredictable by an enemy. The purpose to which she put her idea presumed its applicability to the control of torpedoes by radio and rested on a method of synchronization that would have been clumsy in practice but probably could have been made to work. The device was never actually built, so its design was never tested. Later developers of multiple frequency systems were generally not aware of Hedy’s patent and none of them were guided or inspired by it.
Under the same incentive of improving wartime security that had motivated Hedy’s efforts, military engineers were pushing radio technology hard during the early 1940’s, and they continued to do so after the war was over. A set of techniques they worked on was later grouped under the title, “spread spectrum.” What these communications methods had in common was a reliance on a greater range of frequencies than was needed for the information they transmitted. The advantage they gained was increased protection against noise, jamming and interception.
Spread spectrum was initially confined to the military applications for which it was developed, but in the 1980’s the Federal Communications Commission authorized civilian use, and developers were quick to capitalize on an ability it provided of allowing multiple users to share a common frequency band without interfering with each other, yielding a dramatic expansion of capacity that led to such now-familiar applications as GPS, cell phones and WiFi.
The two most common forms of spread spectrum are called “direct sequence” and “frequency hopping”. A direct sequence transmitter imposes pseudo-random noise on the signals it sends out. This has the effect of expanding the range of frequencies-used and flattening the graph of their spectrum, obscuring the existence of a signal and making its interception and jamming more difficult by those who recognize its presence. The superimposed noise appears random to a potential interceptor, but it’s called pseudo-random because it can be reproduced by anyone who knows the algorithm that was used to create it. In particular, a receiver can be equipped with that algorithm in order to allow it to generate the same noise pattern and subtract it from the received signal to restore the original. Frequency hopping is similar in that it also relies on a pseudo-random generator, but rather than imposing the output as noise, the transmitter uses it to select from a variety of allowed frequencies. A receiver equipped with the same algorithm can use it to change frequencies in synchrony with those being sent.
What Hedy and George proposed is an instance of frequency hopping in which the pseudo-random sequence is punched on paper tapes rather than being incorporated into the electronics. While the underlying idea is the same, the method of implementation does make a difference. Paper ribbons and vacuum-based sensors are prone to mechanical errors and breakdowns. They aren’t capable of changing frequencies as rapidly as electronic methods nor of incorporating the same kinds of error checking and correcting schemes.
Varying transmission frequencies to inhibit jamming is a concept general enough that it can’t be attributed to a single inventor. At its most basic it’s what radio operators do manually from time to time to keep the other side guessing. Starting in 1903 with various patents and publications, Nikola Tesla and others explored the concept in the United States and elsewhere, Germany in particular; and the German army employed a version against the British in World War I. That these developments preceded Hedy’s involvement needn’t detract from her claim to originality. Given the limited knowledge she had of technical developments and the improbability that she executed a thorough patent search, it’s likely she came up with the idea on her own.
For those with enough interest in the subject and understanding of its terms, there is a scholarly article that recounts the history of spread spectrum technology, including frequency hopping, written in 1982 by electrical engineer Robert A. Scholtz. It’s called:
“The Origins of Spread-Spectrum Communications”, IEEE Transactions on Communications, Vol. COM-30, No. 5, May 1982, p. 822
The article doesn’t mention Hedy and George, which merely reflects the fact that their patent played no part in the development of frequency hopping or wireless technology since it lay unknown and unused until it was unearthed by later investigators whose advances had already passed it by. That the concept Hedy latched onto was a good one, is attested to by the degree to which it was exploited by others before and after Hedy’s interest. It also emphasizes the fact that there’s more to inventing than having a good idea or recognizing one. The Army Signal Corps became involved in developing secure radio systems starting in the early 1940’s. Their engineers did achieve successes that were kept classified and therefore unknown to the outside world until the 1980’s; but in spite of their investigations of spread spectrum technology and those of others, Robert Scholtz concludes in the paper cited above: “In 1963 BLADES [a communications system developed by Sylvania for the Navy] was installed on the command flagship Mt. McKinley for operational development tests. … intentional jamming was encountered, and BLADES provided the only useful communication link for the McKinley. Thus, BLADES was quite likely the earliest FH-SS [frequency hopping spread spectrum] communications system to reach an operational state.” (Underlining added.)
Although Hedy’s patent was never acted on, its existence did become known as a result of patent searches initiated by later investigators, the earliest remembered being in 1955 by an engineer who’d intended to use frequency hopping in a design he’d been working on, only to have it superseded by a cabled system. But later researchers of spread spectrum were as surprised as he’d been to find among papers and patents elicited from Bell Labs and Sylvania, the U.S. Army and the Navy, Telefunken and Siemens, and dozens of other centers of electronics research, a patent issued in 1941 to a pair of unaffiliated individuals for a “Secret Communications System” that relied on player piano technology to synchronize changes of frequency between a pair of communicating radios. If the names on the patent had been Helen Kugler Murray, let’s say, and Greg Atley, nobody would have given it a thought, and we would have heard no more about it, but as it turned out they were Hedy Kiesler Markey and George Antheil, and it took only a little effort of memory to recall that Markey was one of the married names of Hedy Lamarr – film star and glamour queen of a bygone era, who’d gone through some tough sledding in the meantime and was living by herself now, with her attempted contribution to the war effort and communications technology of her day having long been forgotten.
Who could let an opportunity like that get away, to introduce some zest into the life of an individual with a past as intriguing as Hedy’s had been? Certainly not Colonel Dave Hughes, veteran of the Korean and Vietnam wars, pioneer in the spread of the internet and wireless communications to rural areas. Born in 1928, Dave had been 9 years old when Hedy arrived in Hollywood and 21 when she’d turned her wiles on an overmatched Samson. Once Dave became aware of the actress’s forays into inventing and the kind of life she was currently living, the thing he set about doing was as good as done. It took three years, but through his efforts and those of the people he enlisted online he saw to it that the recipient of an award he’d been given by the Electronic Frontier Foundation for 1993 was bestowed on Hedy for 1997. It included a posthumous acknowledgement of George’s part as well. So there it was, attested to by a reputable scientific organization – the unarguable importance of Hedy’s contribution to wireless technology.
“In the bleak early days of World War II ensconced in her mansion outside of Hollywood, the World’s Most Beautiful Woman inveigled the Bad Boy of Music into helping her come up with a way to give the Nazis back some of their own. And all that these two unlikely individuals wound up doing was to invent frequency hopping – the crucial first step in the development of spread spectrum technology that’s led through various modes of multiple access to GPS, cell phones, WiFi and all the other wireless services we rely on so heavily today.”
Wait a minute! You can’t put that down. Anybody that knows anything about Hedy Lamarr and George Antheil will realize how phony it is. Not only did Hedy and George not invent frequency hopping, it wasn’t until years after their proposal got shelved by the Navy that anybody found out that the two of them had been given a patent for something that later came to be known under that heading; but none of the people who succeeded in putting frequency hopping and the technologies that followed it to practical use, drew on anything Hedy and George had done.
You’re missing the point. This is the way everybody wishes it had been, the way it should have been, the way it will have been … once the book comes out.
Are you telling me that’s how history gets written?
Of course it is. You mean you didn’t know?
Patented Aug. 11, 1942 2,292387
UNITED STATES PATENT OFFICE
SECRET COMMUNICATION SYSTEM
Hedy Kiesler Markey, Los Angeles, and George Antheil, Manhattan Beach, Calif.
Application June 10, 1941, Serial No. 397,412
6 Claims. (Cl. 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 difiicult 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 l0a and at the end of the operations occupies the position l0b. This mother ship discharges a torpedo 11 that travels successively along different paths 12, 13, 14, 15 and 16 to strike an enemy ship 17, which initially occupies the position 17a but which has moved into the position 17b at the time it is struck by the torpedo 11. According to its original course, the enemy ship 17 would have reached the position 17c, 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 11 can be steered from the mother ship 10a 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 10, or its course may be followed by an observer in an airplane 18 who communicates his findings to the mother ship 10a. It is also possible to control the torpedo directly from the airplane 18 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 10 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 17a 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 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 16, in order to strike the enemy ship 17b.
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 21|, 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 20 is controlled to oscillate at diiferent fre quencies by a plurality of tuning condensers 24a, 24b, 24c, 24d, 24e, 24f, and 24g, adapted to be independently connected to the oscillator by automatically controlled switches 31, one for each condenser. The different condensers 24a to 24g, inclusive, are of different capacities, and these differences are indicated in the drawings by different spacings 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 thereupon modulates the particular carrier wave being generated at that time by the oscillator 20. The modulated carrier wave is then amplifled in the amplifier 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 oscillator 36 to the modulator 21.
The switches 31 are selectively closed by a record-controlled mechanism actuated by a record strip 37, which is drawn off a supply roll 38 over a control head 39 and wound up on a takeup spool 40 driven by a constant-speed clock motor 41.
Referring now to Fig. 4, the record strip 37 has perforations arranged in eight diiferent 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 31 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 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 37.
Each of the passages 46 is communicated by a restricted passage 47 with a suction manifold 48, which is connected by a tube 49 to a suction pump 50. Each of the passages 46 is also connected by a tube 51 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 54 is separated by a block of insulation 55 from the lower end of its associated piston 53. The pistons are normally maintained in upper position in which shoulders 56 thereon lie against the lower face of the cylinder block 57 containing the cylinders 52, 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 thereabove, to carry the movable springs 54 against the cooperating contact springs 58 to close the switches 31.
The pistons 53 are maintained in uppermost position, in which the switches 31 are open, when a solid portion of the record strip 37 overlies the passages 46, but are depressed by the springs 53a. However, 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 37, suction is up plied from the manifold 48 through the restricted passage 47 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 46, air flows freely info the upper end of the passage and into the restricted passage 47, thereby breaking the suction applied to the upper end of the piston 53 and permitting the spring 53a 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 31 will be successively closed, to connect different ones of the tuning condensers 24a to 24g (Fig. 1) inclusive, to the oscillator 20 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 oscillator 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 6I 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 166 and 566, the first of which is tuned to 100-cycles and the second to 500-cycles. The output of the filter 166 is delivered through a rectifier 168 to a magnet 169, and the output of the filter 566 is delivered through a rectifier 568 to a magnet 569. The magnets 169 and 569 act on a common armature 72, which is normally positioned in a neutral position but moves in response to energization of magnet 169 to close on a contact 170 and moves in response to energizaticn of magnet 569 to close on a contact 570.
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 169 and close the armature 72 on the contact 170, thereby completing a circuit from a battery 74 through a solenoid 1715. The solenoid thereupon attracts its plunger 176, causing a pawl 177, connected to the plunger, to be pulled into engagement with ratchet teetg 178 on a rudder wheel 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 169 and the solenoid 175 are released, whereupon the pawl 177 and plunger 176 are retracted into neutral position by the spring I80.
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 175, 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 providedto retain the rudder 83 in whatever position it has been moved by the pawl 177 or 577, and we have shown a brakedrum 84 frictionally engaged by a brakeband 85 and connected by a pinion 86 and a gear segment 87 to the rudder wheel 79. The brakeband 85 offers suflicient 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 61, to tune it to difierent frequencies, by contacts 31′ similar to the contacts 31 at the transmitting station, and actuated in the same way under the control of a record strip 37′, which may be identical with the record strip 37 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 41 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 37′, are the same as those at the transmitting statlon, which were described with reference to Figs. 5 and 6.
It is of course necessary that the record strips 37 and 37′ 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 41 and 41′.
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 101 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’equip- .ment, 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 tothe 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 46 in the control head 39. The perforations in the row H of the record strip occur at the beginning and end of each perforation in rows D, E, F, 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 G, to warn the operator not to transmit a control impulse at the moment of transition from one frequency to another. The lamp 43 remains lighted throughout periods when the transmitter is tuned to transmit in any of the channels A, B, or 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 that 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 as many as 88rows 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 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 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 obvious to those skilled in the art that by using a large number of modulation frequencies, additional functions can be performed. Thus by using four modulation waves having frequencies of say 100-cycles, 500-cycles, 1,000-cycles and 2,000-cycles, respectively, and using appropriate filters at the receiving station, it is obvious that two rudders can be controlled. This would be 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 employed.
Various other departures from the exact system described will be apparent to those skilled in the art, and the invention is, therefore, to: be limited only as set forth in the appended claims.
- In a secret communication system, a transmitting station including means for generating and transmitting carrier waves of a plurality of frequencies, a first elongated record strip having differently characterized, longitudinally disposed recordings thereon, record-actuated means selectively responsive to different ones of said recordings for determining the frequency of said carrier waves, means for moving said strip past said record-actuateed means whereby the carrier wave frequency is changed from time to time in accordance with the recordings on said strip, a receiving station including carrier wave-receiving means having tuning means tunable to said carrier wave 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 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.
- 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 responsive to the lateral positioning of said recordings.
- Apparatus as described in claim 1, in which said record strip comprises a ribbon having longitudinally extending slots therein differently characterized by being 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.
- 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, 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 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.
- Apparatus as described in claim 4, in which said mechanism on said craft 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.
- Apparatus as described in claim 1, including means at the transmitting station for transmitting radio signals of different frequencies to which said radio receiver tuning 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.