US2292387A - Secret communication system - Google Patents

Secret communication system Download PDF

Info

Publication number
US2292387A
US2292387A US39741241A US2292387A US 2292387 A US2292387 A US 2292387A US 39741241 A US39741241 A US 39741241A US 2292387 A US2292387 A US 2292387A
Authority
US
Grant status
Grant
Patent type
Prior art keywords
record
strip
transmitting
torpedo
control
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
Application number
Inventor
Markey Hedy Kiesler
Antheil George
Original Assignee
Markey Hedy Kiesler
Antheil George
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Grant date

Links

Images

Classifications

    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04LTRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L9/00Cryptographic mechanisms or cryptographic arrangements for secret or secure communication
    • H04L9/38Encryption being effected by mechanical apparatus, e.g. rotating cams, switches, keytape punchers
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04LTRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L9/00Cryptographic mechanisms or cryptographic arrangements for secret or secure communication
    • H04L9/12Transmitting and receiving encryption devices synchronised or initially set up in a particular manner
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04LTRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L2209/00Additional information or applications relating to cryptographic mechanisms or cryptographic arrangements for secret or secure communication H04L9/00
    • H04L2209/80Wireless

Description

H. K. MARKEY ETAL, 4 2,292,387

SECRET COMMUNICATION SYSTEM Filed June 10, 1941 2 Sheets-Sheet 2 Patented Aug. 111, 1942 SECRET COMlVIUNICATION SYSTEM Hedy Kiesler Markey, Los Angeles, and George Anthcil, Manhattan Beach, Calif.

Application June 10, 1941, Serial No. 397,412

6 Claims.

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 constantspeed 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 VIVI 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 lllb. This mother ship discharges a. torpedo II that travels successively along different paths l2, l3, I4, l5 and IE to strike an enemy ship II, which initially' occupies the position Ila 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 10, 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 I I was traveling in a straight line substantially parallel to the mother ship ID 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 I! and for water currents represented by the small arrows I9. However, as a result of the change in course of the enemy ship Ila 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 llb.

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 dimcult 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. Suflice it to say that the variable-frequency. carrier oscillator 2|! is controlled to oscillate at diiferent fre quencies 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 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 2|, and at the same time closes contacts 33, which connect a IOU-cycle oscillator 34 to the modulator II, 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 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 2|.

The switches 3| 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 takeup spool 40 driven by a constant-speed clock motor 4|.

Referring now to Fig. 4, the record strip 31 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 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 31 is drawn over the control head responds to perforations in the different rows A to H, inclusive, on the strip, to close the various switches 3| and the switch 42.

A typical construction that may be used in the control head 39 is shown in Figs. 5 and 6. Thus it may comprise a block or shoe 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 6| 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 i"..- sulation 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 3| 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 64 against the cooperating contact springs 58 to close the switches 3|.

The pistons 53 are maintained in uppermost position, in which the switches 3| 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 3|.

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 con densers 24a to 249 (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 ll of Fig. 1), comprises a receiving antenna 6| and a signal selector 6| that may be tuned to any one of four different frequencies by connecting thereto dill'erent condensers 24'd, 24's, 24'}, and 24's. When the condenser 24'd 39, as previously mentioned, and the control head is connected to the selector 6| and the condenser ratchet teeth advance the wheel clockwise by the length of 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 BI 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 lOO-cycles and the second to SOD-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 I66 to energize the magnet I69 and close the armature 12 on the contact I10, thereby completing a circuit from a battery 14 through a solenoid I15. The solenoid thereupon attracts its plunger I16, causing a pawl I11, connected to the plunger, to be pulled into engagement with I18 on a rudder wheel 19 and one of the ratchet teeth. A spring I80 normally maintains the pawl I11 clear of the teeth I18,

and a stationary cam face I8I guides the pawl into engagement with the ratchet teeth as it is moved by the plunger I16.

The rudder wheel 19 is secured to a rudder post 82 carrying a rudder 83, so that the rudder is moved a predetermined distance toward the left in response to a single actuation of the key 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 I 11 and plunger I16 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 12 on the contact 510, to energize a solenoid 515, identical with the solenoid I15, and actuate a pawl 511 which engages with ratchet teeth 518. The latter are oppositely directed with respect to the ratchet teeth I18, so that the pawl 511 and the teeth 518 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 I11 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 19. band 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 I11 and 511.

The tuning condensers 24'd to 24'g, inclusive, at the receiving station are adapted to be con- The brake nected one at a time to the selector 6|, to tune it to difierent 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 3|, whereby the latter are closed in response to differently positioned perforations in the record strip 31', 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 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 I00 (Fig. 6) slidably mounted for vertical movement in the head 45 and adapted to engage a special starting hole IOI (Fig. 4) in its associated record strip. The pin I00 is normally urged into a lower position by a compression spring I02, 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 I03 having a plunger I04 which is connected to the pin I 00. 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 I03 on the torpedo and the solenoid I03 in the transmitting'equip- .ment, are connected in series with a battery I05 by a circuit including conductors I06 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 I06 are broken, thereby interrupting the series energizing circuit of the solenoids I03 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 efiective 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 receivingstations are both tuned tothe same fre- @IIUGHCY. Thelamp43, actuated by the auxiliary switch 42 (Fig. '1) constitutes such an indicator.

Theswitchfl is closed to light'the lamp 43 whenever an aperture in row H (Fig. 4) ,of' the,

record strip moves overits associated passage 4 row of therecord 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, perforationsin these rows (at V which times perforations occur in one or more of the rows, A, B, and C, which transmit false signals).

The, mechanism arrangedas described, func- I 'tions to light the lamp 43v for a short time during each transitionfrom one to another of the useful lighted, that these impulses will not affectv the to pedo. I I I I It will be understood that many variations, from the construction shownv can be made without departing from the invention- Thus in order to simplify thedrawings a record strip having only eight :rows of perforations has been illustrated. However, as previously mentioned, similar record strips employed in player pianos now I I 'h'aveas many as :88rowsof 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 thetransmitter for sending false signals.

If desired, the perforations corresponding to the false signals, may be omitted from the record strip at the receiver. However this is not 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.

' I in the control head as. I The perforations in -desc'rihing in detail its application to thecon trol of a'torpedoor other craft where it is necessary to steer in only one dimension, it will be I obvious to'those skilled in the artthat by using I a large number of modulation frequencies, ad- 'ditional functions canbe performed. Thus by 1 using four modulation waves having frequencies "of say lilo-cycles, 500-cycles, LOGO-cycles and I 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 ver-,

'tical' direction, as well as in a horizontal direction, is desirable. There'is noparticular limit to the numberof control channels that can'be 7 used with our invention.

, I It is also to be understood that other methods of modulation than the conventional oneshown, '20,

lation, Can be employedinour system. Theexpression 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 moduemployed. 1 I

I Various other'departures from the exact system described will be apparent tothoseskilled' in i the art, and the invention' is, therefore, to: be

forth in the appended claims.

limited only, as set 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 conmoving said strip "past' aid regtrolled 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.

US2292387A 1941-06-10 1941-06-10 Secret communication system Expired - Lifetime US2292387A (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
US2292387A US2292387A (en) 1941-06-10 1941-06-10 Secret communication system

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
US2292387A US2292387A (en) 1941-06-10 1941-06-10 Secret communication system

Publications (1)

Publication Number Publication Date
US2292387A true US2292387A (en) 1942-08-11

Family

ID=23571097

Family Applications (1)

Application Number Title Priority Date Filing Date
US2292387A Expired - Lifetime US2292387A (en) 1941-06-10 1941-06-10 Secret communication system

Country Status (1)

Country Link
US (1) US2292387A (en)

Cited By (62)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2707208A (en) * 1945-03-31 1955-04-26 Rca Corp Secrecy facsimile system
US2816720A (en) * 1950-10-11 1957-12-17 Northrop Aircraft Inc Incremental remote radio control system
US2999170A (en) * 1956-05-29 1961-09-05 Gen Electric Co Ltd Receivers for use in electric signalling systems
US5084901A (en) * 1988-12-26 1992-01-28 G.D.S. Co., Ltd. Sequential chirp modulation-type spread spectrum communication system
USRE34004E (en) * 1953-03-30 1992-07-21 Itt Corporation Secure single sideband communication system using modulated noise subcarrier
US6178144B1 (en) 1998-06-02 2001-01-23 Seagate Technology Llc Magneto-optical recording system employing linear recording and playback channels
US6208594B1 (en) 1998-06-02 2001-03-27 Seagate Technology Llc Efficient linearization of saturation channels
US6263268B1 (en) 1997-08-26 2001-07-17 Transcontech Corporation System and method for providing mobile automotive telemetry
US6542443B1 (en) 1999-06-02 2003-04-01 Seagate Technology Llc Efficient linearization of saturation channels
US6676017B1 (en) 2002-11-06 2004-01-13 Smith, Iii Emmitt J. Personal interface device and method
US6687205B1 (en) 1998-06-09 2004-02-03 Seagate Technology Llc Parallel coded spread spectrum communication for data storage
US20040215815A1 (en) * 2003-04-22 2004-10-28 Sony Corporation Data communication system, data communication apparatus and data communication method, connection establishment method and apparatus, connection establishment system, and computer program thereof
US20050063328A1 (en) * 2003-05-02 2005-03-24 Microsoft Corporation Slotted seeded channel hopping for capacity improvement in wireless networks
US20050083977A1 (en) * 2002-02-08 2005-04-21 Moulsley Timothy J. Radio communication system
US20050091493A1 (en) * 1997-04-16 2005-04-28 Sony Corporation Remote control of VCR with electronic mail
US20060074677A1 (en) * 2004-10-01 2006-04-06 At&T Corp. Method and apparatus for preventing speech comprehension by interactive voice response systems
US20070100514A1 (en) * 2005-11-02 2007-05-03 Park Tai S Remote control of conveyance and appliance functions
US20070171060A1 (en) * 2000-09-21 2007-07-26 Trent Douglas E Portable security container
US20070208235A1 (en) * 1993-09-04 2007-09-06 Marcus Besson Wireless medical diagnosis and monitoring equipment
US20070244614A1 (en) * 1997-08-26 2007-10-18 Paxgrid Telemetric Systems, Inc. Automotive telemetry protocol
US20070297524A1 (en) * 2006-06-13 2007-12-27 Ben Jones Approach for spectrum analysis in a receiver
US20080002831A1 (en) * 2001-05-30 2008-01-03 Palmsource, Inc. System and method for prioritizing and balancing simultaneous audio outputs in a handheld device
US7386588B2 (en) 1998-05-29 2008-06-10 Research In Motion Limited System and method for pushing information from a host system to a mobile data communication device
US20080186932A1 (en) * 2007-02-05 2008-08-07 Duy Khuong Do Approach For Mitigating The Effects Of Rogue Wireless Access Points
US20090041096A1 (en) * 2007-08-02 2009-02-12 Bae Systems Information And Electronic Systems Integration Inc. Efficient synchronization of a spread spectrum signal in the presence of delay and frequency uncertainty
US7498999B2 (en) 2004-11-22 2009-03-03 Ruckus Wireless, Inc. Circuit board having a peripheral antenna apparatus with selectable antenna elements and selectable phase shifting
US7498996B2 (en) 2004-08-18 2009-03-03 Ruckus Wireless, Inc. Antennas with polarization diversity
US7511680B2 (en) 2004-08-18 2009-03-31 Ruckus Wireless, Inc. Minimized antenna apparatus with selectable elements
US7525486B2 (en) 2004-11-22 2009-04-28 Ruckus Wireless, Inc. Increased wireless coverage patterns
WO2009057626A1 (en) 2007-10-29 2009-05-07 Tokyo Institute Of Technology Physical amount detection device
US7561020B2 (en) 2005-06-27 2009-07-14 The Chamberlain Group, Inc. System and method for using operator as a repeater
US7589615B2 (en) 2004-11-22 2009-09-15 The Chamberlain Group, Inc. Multi-frequency security code transmission and reception
US7639106B2 (en) 2006-04-28 2009-12-29 Ruckus Wireless, Inc. PIN diode network for multiband RF coupling
US7646343B2 (en) 2005-06-24 2010-01-12 Ruckus Wireless, Inc. Multiple-input multiple-output wireless antennas
US7652632B2 (en) 2004-08-18 2010-01-26 Ruckus Wireless, Inc. Multiband omnidirectional planar antenna apparatus with selectable elements
US20100087156A1 (en) * 2008-10-07 2010-04-08 The Chamberlain Group, Inc. Method and Apparatus to Facilitate Using Multiple Carrier Frequencies
US7696946B2 (en) 2004-08-18 2010-04-13 Ruckus Wireless, Inc. Reducing stray capacitance in antenna element switching
US20100184384A1 (en) * 2009-01-21 2010-07-22 Ben William Jones Integrated Circuit For Signal Analysis
US20100184395A1 (en) * 2009-01-21 2010-07-22 Nils Bagge Adaptive Channel Scanning For Detection And Classification Of RF Signals
US20100254432A1 (en) * 2009-04-03 2010-10-07 Charles Martin Transmitter-emitter system using frequency hopping with unidirectional communication
US20100301999A1 (en) * 2009-05-27 2010-12-02 Overhead Door Corporation Channel-switching remote controlled barrier opening system
US7880683B2 (en) 2004-08-18 2011-02-01 Ruckus Wireless, Inc. Antennas with polarization diversity
US7965252B2 (en) 2004-08-18 2011-06-21 Ruckus Wireless, Inc. Dual polarization antenna array with increased wireless coverage
US20110153471A1 (en) * 2002-01-04 2011-06-23 Davis Jr Tommy Lee Equipment management system
US20110216809A1 (en) * 2001-01-25 2011-09-08 Bandspeed, Inc. Approach For Managing The Use Of Communications Channels Based On Performance
US8023899B2 (en) 2009-04-30 2011-09-20 Bandspeed, Inc. Approach for selecting communications channels in communication systems to avoid interference
US20110231546A1 (en) * 1997-08-26 2011-09-22 Nathanson Martin D Automotive telemetry protocol
US8031129B2 (en) 2004-08-18 2011-10-04 Ruckus Wireless, Inc. Dual band dual polarization antenna array
US8068068B2 (en) 2005-06-24 2011-11-29 Ruckus Wireless, Inc. Coverage antenna apparatus with selectable horizontal and vertical polarization elements
US8117344B2 (en) 1996-12-13 2012-02-14 Visto Corporation Global server for authenticating access to remote services
US8217843B2 (en) 2009-03-13 2012-07-10 Ruckus Wireless, Inc. Adjustment of radiation patterns utilizing a position sensor
US8686905B2 (en) 2007-01-08 2014-04-01 Ruckus Wireless, Inc. Pattern shaping of RF emission patterns
US8698675B2 (en) 2009-05-12 2014-04-15 Ruckus Wireless, Inc. Mountable antenna elements for dual band antenna
US8756668B2 (en) 2012-02-09 2014-06-17 Ruckus Wireless, Inc. Dynamic PSK for hotspots
US8786495B2 (en) 2010-07-14 2014-07-22 Zebra Enterprise Solutions Corp. Frequency channel diversity for real-time locating systems, methods, and computer program products
US8842630B2 (en) 2010-12-17 2014-09-23 Cisco Technology, Inc. Extendable frequency hopping timeslots in wireless networks
US20150032607A1 (en) * 2005-06-30 2015-01-29 Innova Electronics, Inc. Mobile device based vehicle diagnostic system
US9019165B2 (en) 2004-08-18 2015-04-28 Ruckus Wireless, Inc. Antenna with selectable elements for use in wireless communications
US9092610B2 (en) 2012-04-04 2015-07-28 Ruckus Wireless, Inc. Key assignment for a brand
US9407012B2 (en) 2010-09-21 2016-08-02 Ruckus Wireless, Inc. Antenna with dual polarization and mountable antenna elements
US9570799B2 (en) 2012-09-07 2017-02-14 Ruckus Wireless, Inc. Multiband monopole antenna apparatus with ground plane aperture
US9634403B2 (en) 2012-02-14 2017-04-25 Ruckus Wireless, Inc. Radio frequency emission pattern shaping

Cited By (115)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2707208A (en) * 1945-03-31 1955-04-26 Rca Corp Secrecy facsimile system
US2816720A (en) * 1950-10-11 1957-12-17 Northrop Aircraft Inc Incremental remote radio control system
USRE34004E (en) * 1953-03-30 1992-07-21 Itt Corporation Secure single sideband communication system using modulated noise subcarrier
US2999170A (en) * 1956-05-29 1961-09-05 Gen Electric Co Ltd Receivers for use in electric signalling systems
US5084901A (en) * 1988-12-26 1992-01-28 G.D.S. Co., Ltd. Sequential chirp modulation-type spread spectrum communication system
US20070208235A1 (en) * 1993-09-04 2007-09-06 Marcus Besson Wireless medical diagnosis and monitoring equipment
US8771184B2 (en) 1993-09-04 2014-07-08 Body Science Llc Wireless medical diagnosis and monitoring equipment
US9361603B2 (en) 1996-12-13 2016-06-07 Good Technology Corporation System and method for globally and securely accessing unified information in a computer network
US8117344B2 (en) 1996-12-13 2012-02-14 Visto Corporation Global server for authenticating access to remote services
US8812702B2 (en) 1996-12-13 2014-08-19 Good Technology Corporation System and method for globally and securely accessing unified information in a computer network
US8745167B2 (en) 1996-12-13 2014-06-03 Good Technology Corporation System and method for globally and securely accessing unified information in a computer network
US6925567B1 (en) * 1997-04-16 2005-08-02 Sony Corporation Remote control of VCR with electronic mail
US7143296B2 (en) 1997-04-16 2006-11-28 Sony Corporation Transmitting/receiving apparatus and a transmitting/receiving method
US7376843B2 (en) 1997-04-16 2008-05-20 Sony Corporation Remote control of VCR with electronic mail
US20050091493A1 (en) * 1997-04-16 2005-04-28 Sony Corporation Remote control of VCR with electronic mail
US20050160283A1 (en) * 1997-04-16 2005-07-21 Sony Corporation Transmitting/receiving apparatus and a transmitting/receiving method
US7454626B2 (en) 1997-04-16 2008-11-18 Sony Corporation Transmitting/receiving apparatus and a transmitting/receiving method
US8560609B2 (en) 1997-08-26 2013-10-15 Paxgrid Telemetric Systems, Inc Automotive telemetry protocol
US7593999B2 (en) 1997-08-26 2009-09-22 Paxgrid Telemetric Systems, Inc. Automotive telemetry protocol
US20110231546A1 (en) * 1997-08-26 2011-09-22 Nathanson Martin D Automotive telemetry protocol
US20070244614A1 (en) * 1997-08-26 2007-10-18 Paxgrid Telemetric Systems, Inc. Automotive telemetry protocol
US6263268B1 (en) 1997-08-26 2001-07-17 Transcontech Corporation System and method for providing mobile automotive telemetry
US7509376B2 (en) 1998-05-29 2009-03-24 Research In Motion Limited System and method for redirecting message attachments between a host system and a mobile data communication device
US7386588B2 (en) 1998-05-29 2008-06-10 Research In Motion Limited System and method for pushing information from a host system to a mobile data communication device
US6178144B1 (en) 1998-06-02 2001-01-23 Seagate Technology Llc Magneto-optical recording system employing linear recording and playback channels
US6208594B1 (en) 1998-06-02 2001-03-27 Seagate Technology Llc Efficient linearization of saturation channels
US6687205B1 (en) 1998-06-09 2004-02-03 Seagate Technology Llc Parallel coded spread spectrum communication for data storage
US6542443B1 (en) 1999-06-02 2003-04-01 Seagate Technology Llc Efficient linearization of saturation channels
US20070171060A1 (en) * 2000-09-21 2007-07-26 Trent Douglas E Portable security container
US8873500B2 (en) 2001-01-25 2014-10-28 Bandspeed, Inc. Approach for managing the use of communications channels based on performance
US8542643B2 (en) 2001-01-25 2013-09-24 Bandspeed, Inc. Approach for managing the use of communications channels based on performance
US9883520B2 (en) 2001-01-25 2018-01-30 Bandspeed, Inc. Approach for managing the use of communications channels based on performance
US20110216809A1 (en) * 2001-01-25 2011-09-08 Bandspeed, Inc. Approach For Managing The Use Of Communications Channels Based On Performance
US9379769B2 (en) 2001-01-25 2016-06-28 Bandspeed, Inc. Approach for managing the use of communications channels based on performance
US20080002831A1 (en) * 2001-05-30 2008-01-03 Palmsource, Inc. System and method for prioritizing and balancing simultaneous audio outputs in a handheld device
US8370225B2 (en) 2002-01-04 2013-02-05 Prova Group, Inc. Equipment management system
US8898077B2 (en) 2002-01-04 2014-11-25 Prova Group, Inc. System and method for tracking authenticated items
US20110153471A1 (en) * 2002-01-04 2011-06-23 Davis Jr Tommy Lee Equipment management system
US8199711B2 (en) 2002-02-08 2012-06-12 Koninklijke Philips Electronics N.V. Radio communication system
US20050083977A1 (en) * 2002-02-08 2005-04-21 Moulsley Timothy J. Radio communication system
US7554943B2 (en) * 2002-02-08 2009-06-30 Koninklijke Philips Electronics N.V. Radio communication system
US7974929B2 (en) 2002-11-06 2011-07-05 Smith Iii Emmitt J Personal interface device and method
US8380636B2 (en) 2002-11-06 2013-02-19 Emmitt J. Smith, III Personal interface device and method
US6676017B1 (en) 2002-11-06 2004-01-13 Smith, Iii Emmitt J. Personal interface device and method
US20040098353A1 (en) * 2002-11-06 2004-05-20 Smith Emmitt J. Personal interface device and method
US7652997B2 (en) * 2003-04-22 2010-01-26 Sony Corporation Data communication system, data communication apparatus and data communication method, connection establishment method and apparatus, connection establishment system, and computer program thereof
US20040215815A1 (en) * 2003-04-22 2004-10-28 Sony Corporation Data communication system, data communication apparatus and data communication method, connection establishment method and apparatus, connection establishment system, and computer program thereof
US20050063328A1 (en) * 2003-05-02 2005-03-24 Microsoft Corporation Slotted seeded channel hopping for capacity improvement in wireless networks
US7379447B2 (en) * 2003-05-02 2008-05-27 Microsoft Corporation Slotted seeded channel hopping for capacity improvement in wireless networks
US9019165B2 (en) 2004-08-18 2015-04-28 Ruckus Wireless, Inc. Antenna with selectable elements for use in wireless communications
US7696946B2 (en) 2004-08-18 2010-04-13 Ruckus Wireless, Inc. Reducing stray capacitance in antenna element switching
US8314749B2 (en) 2004-08-18 2012-11-20 Ruckus Wireless, Inc. Dual band dual polarization antenna array
US7511680B2 (en) 2004-08-18 2009-03-31 Ruckus Wireless, Inc. Minimized antenna apparatus with selectable elements
US7498996B2 (en) 2004-08-18 2009-03-03 Ruckus Wireless, Inc. Antennas with polarization diversity
US8031129B2 (en) 2004-08-18 2011-10-04 Ruckus Wireless, Inc. Dual band dual polarization antenna array
US7652632B2 (en) 2004-08-18 2010-01-26 Ruckus Wireless, Inc. Multiband omnidirectional planar antenna apparatus with selectable elements
US8860629B2 (en) 2004-08-18 2014-10-14 Ruckus Wireless, Inc. Dual band dual polarization antenna array
US9837711B2 (en) 2004-08-18 2017-12-05 Ruckus Wireless, Inc. Antenna with selectable elements for use in wireless communications
US7965252B2 (en) 2004-08-18 2011-06-21 Ruckus Wireless, Inc. Dual polarization antenna array with increased wireless coverage
US9077071B2 (en) 2004-08-18 2015-07-07 Ruckus Wireless, Inc. Antenna with polarization diversity
US7880683B2 (en) 2004-08-18 2011-02-01 Ruckus Wireless, Inc. Antennas with polarization diversity
US7558389B2 (en) * 2004-10-01 2009-07-07 At&T Intellectual Property Ii, L.P. Method and system of generating a speech signal with overlayed random frequency signal
US20060074677A1 (en) * 2004-10-01 2006-04-06 At&T Corp. Method and apparatus for preventing speech comprehension by interactive voice response systems
US20090228271A1 (en) * 2004-10-01 2009-09-10 At&T Corp. Method and System for Preventing Speech Comprehension by Interactive Voice Response Systems
CN1758330B (en) 2004-10-01 2010-06-16 美国电报电话公司 Method and apparatus for preventing speech comprehension by interactive voice response systems
US7979274B2 (en) 2004-10-01 2011-07-12 At&T Intellectual Property Ii, Lp Method and system for preventing speech comprehension by interactive voice response systems
US7589615B2 (en) 2004-11-22 2009-09-15 The Chamberlain Group, Inc. Multi-frequency security code transmission and reception
US7498999B2 (en) 2004-11-22 2009-03-03 Ruckus Wireless, Inc. Circuit board having a peripheral antenna apparatus with selectable antenna elements and selectable phase shifting
US7525486B2 (en) 2004-11-22 2009-04-28 Ruckus Wireless, Inc. Increased wireless coverage patterns
US9379456B2 (en) 2004-11-22 2016-06-28 Ruckus Wireless, Inc. Antenna array
US9093758B2 (en) 2004-12-09 2015-07-28 Ruckus Wireless, Inc. Coverage antenna apparatus with selectable horizontal and vertical polarization elements
US9270029B2 (en) 2005-01-21 2016-02-23 Ruckus Wireless, Inc. Pattern shaping of RF emission patterns
US8704720B2 (en) 2005-06-24 2014-04-22 Ruckus Wireless, Inc. Coverage antenna apparatus with selectable horizontal and vertical polarization elements
US8068068B2 (en) 2005-06-24 2011-11-29 Ruckus Wireless, Inc. Coverage antenna apparatus with selectable horizontal and vertical polarization elements
US7675474B2 (en) 2005-06-24 2010-03-09 Ruckus Wireless, Inc. Horizontal multiple-input multiple-output wireless antennas
US9577346B2 (en) 2005-06-24 2017-02-21 Ruckus Wireless, Inc. Vertical multiple-input multiple-output wireless antennas
US7646343B2 (en) 2005-06-24 2010-01-12 Ruckus Wireless, Inc. Multiple-input multiple-output wireless antennas
US8836606B2 (en) 2005-06-24 2014-09-16 Ruckus Wireless, Inc. Coverage antenna apparatus with selectable horizontal and vertical polarization elements
US7561020B2 (en) 2005-06-27 2009-07-14 The Chamberlain Group, Inc. System and method for using operator as a repeater
US9824507B2 (en) * 2005-06-30 2017-11-21 Innova Electronics Corporation Mobile device based vehicle diagnostic system
US20150032607A1 (en) * 2005-06-30 2015-01-29 Innova Electronics, Inc. Mobile device based vehicle diagnostic system
US20070100514A1 (en) * 2005-11-02 2007-05-03 Park Tai S Remote control of conveyance and appliance functions
US7639106B2 (en) 2006-04-28 2009-12-29 Ruckus Wireless, Inc. PIN diode network for multiband RF coupling
US8023575B2 (en) 2006-06-13 2011-09-20 Bandspeed, Inc. Approach for spectrum analysis in a receiver
US20070297524A1 (en) * 2006-06-13 2007-12-27 Ben Jones Approach for spectrum analysis in a receiver
US8686905B2 (en) 2007-01-08 2014-04-01 Ruckus Wireless, Inc. Pattern shaping of RF emission patterns
US20080186932A1 (en) * 2007-02-05 2008-08-07 Duy Khuong Do Approach For Mitigating The Effects Of Rogue Wireless Access Points
US20090041096A1 (en) * 2007-08-02 2009-02-12 Bae Systems Information And Electronic Systems Integration Inc. Efficient synchronization of a spread spectrum signal in the presence of delay and frequency uncertainty
US20100308816A1 (en) * 2007-10-29 2010-12-09 Tokyo Institute Of Technology Physical quantity detection device
WO2009057626A1 (en) 2007-10-29 2009-05-07 Tokyo Institute Of Technology Physical amount detection device
US20100087156A1 (en) * 2008-10-07 2010-04-08 The Chamberlain Group, Inc. Method and Apparatus to Facilitate Using Multiple Carrier Frequencies
US8331928B2 (en) 2008-10-07 2012-12-11 The Chamberlain Group, Inc. Method and apparatus to facilitate using multiple carrier frequencies
US8849213B2 (en) 2009-01-21 2014-09-30 Bandspeed, Inc. Integrated circuit for signal analysis
US20100184395A1 (en) * 2009-01-21 2010-07-22 Nils Bagge Adaptive Channel Scanning For Detection And Classification Of RF Signals
US8447252B2 (en) 2009-01-21 2013-05-21 Bandspeed, Inc. Adaptive channel scanning for detection and classification of RF signals
US20100184384A1 (en) * 2009-01-21 2010-07-22 Ben William Jones Integrated Circuit For Signal Analysis
US8723741B2 (en) 2009-03-13 2014-05-13 Ruckus Wireless, Inc. Adjustment of radiation patterns utilizing a position sensor
US8217843B2 (en) 2009-03-13 2012-07-10 Ruckus Wireless, Inc. Adjustment of radiation patterns utilizing a position sensor
US20100254432A1 (en) * 2009-04-03 2010-10-07 Charles Martin Transmitter-emitter system using frequency hopping with unidirectional communication
US8023899B2 (en) 2009-04-30 2011-09-20 Bandspeed, Inc. Approach for selecting communications channels in communication systems to avoid interference
US8698675B2 (en) 2009-05-12 2014-04-15 Ruckus Wireless, Inc. Mountable antenna elements for dual band antenna
US9419344B2 (en) 2009-05-12 2016-08-16 Ruckus Wireless, Inc. Mountable antenna elements for dual band antenna
US8970345B2 (en) 2009-05-27 2015-03-03 Overhead Door Corporation Channel-switching remote controlled barrier opening system
US20100301999A1 (en) * 2009-05-27 2010-12-02 Overhead Door Corporation Channel-switching remote controlled barrier opening system
US8581695B2 (en) 2009-05-27 2013-11-12 Grant B. Carlson Channel-switching remote controlled barrier opening system
US9483935B2 (en) 2009-05-27 2016-11-01 Overhead Door Corporation Channel-switching remote controlled barrier opening system
US9684054B2 (en) 2010-07-14 2017-06-20 Zih Corp. Frequency channel diversity for real-time locating systems, methods, and computer program products
US8786495B2 (en) 2010-07-14 2014-07-22 Zebra Enterprise Solutions Corp. Frequency channel diversity for real-time locating systems, methods, and computer program products
US9407012B2 (en) 2010-09-21 2016-08-02 Ruckus Wireless, Inc. Antenna with dual polarization and mountable antenna elements
US8842630B2 (en) 2010-12-17 2014-09-23 Cisco Technology, Inc. Extendable frequency hopping timeslots in wireless networks
US9226146B2 (en) 2012-02-09 2015-12-29 Ruckus Wireless, Inc. Dynamic PSK for hotspots
US8756668B2 (en) 2012-02-09 2014-06-17 Ruckus Wireless, Inc. Dynamic PSK for hotspots
US9634403B2 (en) 2012-02-14 2017-04-25 Ruckus Wireless, Inc. Radio frequency emission pattern shaping
US9092610B2 (en) 2012-04-04 2015-07-28 Ruckus Wireless, Inc. Key assignment for a brand
US9570799B2 (en) 2012-09-07 2017-02-14 Ruckus Wireless, Inc. Multiband monopole antenna apparatus with ground plane aperture

Similar Documents

Publication Publication Date Title
US3445815A (en) Central to remote station signalling system
US3601587A (en) Register control system and method
US3098220A (en) Personal call system
US4031330A (en) Digital radio transmission system
US2972140A (en) Apparatus and method for communication through the sense of touch
US3550124A (en) Radar-telemetry system
US2462069A (en) Radio communication system
US3403381A (en) System for radio communication by asynchronous transmission of pulses containing address information and command information
US2524782A (en) Selective calling system
US2418116A (en) Multiplex synchronizing system
US2325829A (en) Signaling system
US1869659A (en) Method of maintaining secrecy in the transmission of wireless telegraphic messages
US2412974A (en) Electric wave communication system
US2421017A (en) Communication and guiding system
US2157122A (en) Warning system for indicating the proximity of aircraft
US2283523A (en) Scanning radio receiver
US3406391A (en) Vehicle identification system
US3900873A (en) Installation for measurement by radio-electric transmission of a distance between two stations
US2404354A (en) Secret signaling system
US1892431A (en) Echo torpedo
US3746991A (en) Remote control communications system
US2173154A (en) Telecontrol system
US3521068A (en) Optical time division multiplex communication system
US2421106A (en) Airway traffic control system
US2960573A (en) Electric carrier current communication systems