US2301475A

US2301475A - Communication system

Info

Publication number: US2301475A
Application number: US312350A
Authority: US
Inventors: Nathan H Suren; William W Carter
Original assignee: Individual
Current assignee: Individual
Priority date: 1940-01-04
Filing date: 1940-01-04
Publication date: 1942-11-10
Anticipated expiration: 1959-11-10

Description

Nov. 10, 1942. N. H. suREN ETAL COMMUNICATION SYSTEM 5 Sheets-Sheet 1` Filed Jan. 4, 1940 TPI/111) TIPP' Y l ramw.;

Nov. 10, 1942. N. H. suREN ETAL 2,301,475

COMMUNICATION SYSTEM Filed Jan. 4, 1940 V 5 SheetS-Sheel 4 Nov. l0, 1942. N. H. sUREN FAI. 2,301,475

COMMUNICATION SYSTEM Filed Jan. 4, 1940 5 sheets-sheet 5 yl yf l WM Patented Nov. l0, 1942 UNETE STATES 'iliiii @FREE CMRIUNCATGN SYSTEM Application January 4, 1940, Serial N 312,350

(Cl. Z50-S) 7 Claims.

The subject of the present invention is a method of transmitting private or secret signals or messages by public channels of communication, i. e., radio waves and telephone wires. Its object is to enable radio frequencies, which may be in use simultaneously for public broadcasts and other purposes, or telephone lines which also may be in use for ordinary purposes, to be used Without interruption of, or interference with, their normal functions, for the transmission of code messages, signals, etc. to selective receivers. A further object is to provide a means of exclusive selectivity whereby a signal intended for one denite receiver, and only the signals so intended, will be received by that receiver only. A further object is to devise a system of code signal transmission whi-ch cannot be readily intercepted, and of which the probabilities of successful decoding are so small as to be practically an irnpossibility. A still further object is to provide means by which such a code message may be sent and recorded by the authorized receiver in intelligible form requiring no subsequent decoding.

Other and related objects are set forth in the following explanation of the invention.

In its generic aspects the system of this invention consists in generating a group of mechanical vibrations (within which term we include sound vibrations) of two or more different frequencies, which may be audible or inaudible frequencies but are within the range of selectivity of available selectors; interrupting such vibrations at such intervals of time that their persistence between interruptions is very brief, but only while all the vibrations of a given group are being generated simultaneously; converting such mechanical vibrations into electrical vibrations either by a wireless transmitter or a telephone transmitter; receiving the vibrations in a group of tuned selectors of which each selector is responsive to the vibrations of one frequency only; converting the received vibrations into mechanical motion; and causing such mechanical motion to operate a recording instrument or develop souni waves.

The vibrations at the transmitting end are produced intermittently, or interrupted, according to a predetermined code of signals and the impulses converted by the receiver reproduce the signals audibly or on a printing recorder, or both. The code may be the common dot and dash system or impulses utilized according to some predetermined plan to operate a printing apparatus Illustrative embodiments of the principles thus briefly summarized are described and explained in the following speciiication and illustrated in the accompanying drawings.

In the drawings,

Fig. lis a diagram of a complete wireless transmission system embodying our invention;

Fig. 2 is a diagram of one form of selector adapted to be tuned to lter out all vibrations except those of one given frequency, within an extremely narrow range;

Fig. 3 is a rear elevation and Fig. 4 a side view of a signal generating machine organized to formulate code messages for transmission according to this invention;

Fig. 5 is a partial development of the type wheel used in this machine and in the recording machine subsequently described;

Fig. 6 is a rear elevation and Fig. 7 a side elevation of a recording apparatus adapted to print intelligibly code messages transmitted electrically from the sender shown in Figs. 3 and 4;

Fig. 8 is a diagram showing a system organized to receive selectively at diierent points signals sent by means of vibrations of six different frequencies used three at a time simultaneously;

Fig. 9 is a diagram showing a simplification of yne reeciving end of the system shown in Fig. -8 where a group of recorders are located in such proximity to one another as to be controllable by mechanically connected switches;

Fig. 10 shows the receiving end of a system such as that represented in Fig. 8, with modifications enabling the recorders to be activated by groups of three vibration frequencies when the different vibrations are initiated progressively as distinguished from simultaneously,

Like reference characters designate the same parts wherever they occur in all the gures.

The system represented by Fig. l consists of a sending station designated as a whole as A and a receiving station designated as a whole as B. The equipment of the sending station comprises a vibration generator a, a signal instrument b, an amplier c, which may be omitted when amplication is not needed, and a transmitter cl For wireless transmission the transmitter may be any L :ncwn producer of radio waves connected with an antenna e. For signalling over a telephone circuit, the ordinary telephone transmitter will serve. The vibration generator and signal sender may be combined in one instrument as will presently appear.

The `vibrations generated for this purpose may be of any frequencies within practical limits. That is, the lowest frequency possible to be used is limited by the selectivity of the receiving selector,its ability to isolate a given frequency from adjacent frequencies And the high limit in radio transmission is established for practical use by the law fixing the band width between channels. As the difference between radio frequencies is fixed by law at 10,0G0Vcycles per second, the highest imposed frequency permissible for our system under present laws is 5,000 cycles per second. But in principle the highest frequency usable is limited only by the qualities of the selector.

It will be seen therefore that in practice our controlling frequencies are limited to those within the audible range, although in principle they may be outside of that range.

Vibration frequencies corresponding to the notes of the chromatic scale, or with intervals between frequencies equal to those between notes of that scale, may be used. for we have found it feasible with available tuning means to make selectors capable of discriminating between notes one half tone apart. Thus the notes of the standard scale, or intermediate tones, with sufficient intervals between tones of the series, may be used for our purpose. We will in the following description refer at times to the frequencies herein discussed as tones or notes.

Such tones may be produced by any one of many well known means, such as tuned strings, reeds, forks, pipes, sound records, etc., and may be produced intermittently at longer or shorter time intervals like or proportional to those of the dot and dash code. Or the sound vibrations may be converted into electrical undulations or vibrations and interrupted intermittently by manually or automatically operated means to produce dot and dash code signals.

The conversion of mechanical vibrations into the corresponding electrical equivalents and modulation of the radio carrier wave by such electrical vibrations are effected by the standard equipment used for radio broadcasting or any other suitable means known to radio engineers. As standard equipment is suitable for the transmission, and also the reception, of the radio wave modulations in the performance of our invention, we have deemed it unnecessary to show the transmitter amplifier or receiver in detail.

The receiving station comprises a receiver f, which may be the same as any standard radio receiver capable of being tuned to carrier waves y of different frequencies, a selector g by which the controlling frequencies of our invention are segregated from other frequencies. a collection of relays and switches in circuit with a source of power, all comprehensively designated by h, and a recorder z'. The selector, relays, and recorder are hereinafter more fully described.

The foregoing description is suflicient for an understanding of the basic principles of the invention. It will be understood that group of two, three or more different frequencies, which will be assumed for the purposes of this description to be those corresponding to any different musical notes, are produced with interruptions by the generating andisignalling means a, b. At the receiving station these vibrations activate an equal number of tuned selectors, and only selectors which are tuned to those specnc frequencies.

Relays operated'by the energy delivered from the selectors lclose electric circuits Venabling power from a battery or other power source to initiate mechanical impulses by which effects 'corresponding to the original signal are obtained.

, Selectors capable of being tuned within close limits to' specic tones are known, and in Fig.

2 we have shown illustratively one which is suitable for our purpose. This includes a transformer T of which the primary winding y is connected to the receiver f so as to carry the radio frequency with all its modulations. The secondary winding Ic of this transformer is connected with a bridge l, one arm of which con-f Vthe secondary winding n is connected to the relay. To obtain the selected note in usable form,

an auxiliary circuit o is used, having a winding p arranged as a secondary to the transformer T, a winding q arranged as a primary to the output transformer T2 and in opposition to the winding m, and a volume controller 1. This auxiliary circuit passes all tones received by the input transformer T. By setting the volume controller r so that the electrical waves in the two circuits have the same intensity, then, as the primaries m and q are in opposition, the same frequencies in each circuit will cancel out, and only the selected frequency will issue from the secondary winding of the output transformer. Each receiving station is equipped with as many such selectors as the number of tones used 'for controlling it. Other selectors than the specic one illustrated may be used within the scope of our' invention. This illustration is intended to typify by one concrete embodiment the generic idea of a tuned selector.

An illustrative embodiment of vibration generating, signal sending, and signal receiving means is shown in Figs. 3 7 similarly typifying the generic idea of means forthis purpose. The generating and sending apparatus is shown in Figs. 3 and fl. It includes a source of mechanical power H, which may be a spring motor, an electrical torque motor, or any other prime mover capable of being stopped instantly when obstructed and of starting instantly when released and is regulated to run at a prescribed rate of speed. It drives through a gear train l2, i3 a phonograph disk l on the circumference of which is a track or groove having a predeter-4 mined number of like wave groups spaced apart from one another. Each wave group is the resultant of two or more vibration frequencies, like any phonographic record of a musical chord. When the disk is set in motion its track vibrates a needle l5, such as a phonograph needle, which operates an electrical pick up I6, from which electrical undulations are conducted to the transmitter d of Fig. l to modulate the radio wave. This part of the apparatus may be the same as the means employed fer broadcasting phonographic transcriptions;

The disk I4 is coupled by a speed reducing gear train l1, I8, I9 and 2G to a shaft 2! on which are mounted a type wheel 22 and a drum 23. This drum is associated with a keyboard (Fig. 4) having keys 245 analogous to typewriter keys, each of which is carried by a lever 25. All the key levers are pivoted side by side on a shaft 25 and each is coupled to a stop lever 2l by suitable means such as gear teeth 23 on a second arm of the stop lever and on a portion of the key lever respectively. All of the stop levers 27 are mounted side by side on a shaft 29 parallel to the shaft 2l, and each has a toe 30 adjacent to the circumference of the drum. Individual springs 3l are connected to the several key levers and to a stationary anchorage in a manner to hold the keys normally raised and the stop levers El normally withdrawn from the circumference` of the drum. When any key is depressed its corresponding stop lever is moved toward the surface of the drum. Each key lever has a rearwardly extending arm 32 which is raised when the corresponding key is depressed, and is formed with a cam surface 33 beneath a latch bar 34. The latch bar is suspended by arms 35 at its opposite ends from a pivot shaft or pivots 35 and is located in a position such that rise of any key lever arm 32 dispiaces it rearwardly and the arm is able to pass clear of the latch bar while its'associated stop lever approaches the drum 23. A spring 3'! is provided to return the latch bar after any of the arms 32 has passed it, and thus retain this arm in raised position, and the associated stop lever 21 in position near the drum, until the latch is again displaced by op.- eration of another key or by other means.

The drum carries outwardly `projecting stops 38, each in the same plane perpendicular to the axis of the drum with one of the stop levers, whereby any stop lever when advanced by depression of a key is enabled to arrest the rotating drum. Preferably there are two, three or more of the stops 33 in the same plane with each stop lever in order to increase the difficulty of deciphering intercepted code messages. Such stops may be made as pins set into the circumference of a continuous drum, but for simplicity and ease of manufacture, the drum is preferably made of a series of disks equal in number to the stop levers 2l and equally spaced therewith,

keyed to shaft 2l and made with projections.4

forming the stops 38 in suitable angular relationship with the projections on other disks.

The type wheel 22 carries printing types on its circumference representing characters such as the letters of the alphabet, the numerals, and marks of punctuation; or other characters or symbols which may be used conventionally or arbitrarily as a means of intelligibly recording. corriiriunicationsl Each key is appropriated to one of such characters or symbols, and the stops 38 on the drum 23 are located in suitable angular relationship to the characters on the type wheel and to the stop levers so as to arrest the type wheel with any selected character in a predetermined zero position when the key corresponding to that character is depressed.

The aero position referred to may be that which enables a printed record toV be made of the seiected character, and in the present illustration is the uppermost point of the wheel. A printing attachment is here shown consisting of a paper tape 39 passing from a supply roll 4B to a take up roll 4I around guide roils 42 located near the type wheel, an inked ribbon 43 passing between the type wheelv and paper around guide rolls M, and a hammer '35 at the outer side of the paper adapted to strike the paper and ribbon against the type which is in zero position.

For conveying intelligence by means of the Roman alphabet and Arabie numerals, with punctuation, a total of about forty, or a few more, characters is suiicient. But to increase the difficulty oi deciphering, two or more series of characters are provided in which the characters are arranged in different sequences. For instance, the characters may be arranged in conventional order in one series, in inverted order in another series, and in jumbled order in still another series; or they may be differently jumbled in two or more series. But however they may be arranged, the stops 38 which cooperate with any one stop lever are spaced so that whenever the key related to that stop lever is depressed, the corresponding character in one or another series will be arrested in the zero position. In other words, all stops 38 of the same disk, or in the same Zone of the drum, are separated from one another with an angular spacing equal to that between the repetitions of the same character on the type wheel.

Each key, when depressed, releases the stop lever previously in arresting positiorrby disf placement of the latch bar effected through the cam surface on the rear arm 32 of the key lever. In order that the release of a previously latehed key lever shall certainly occur, the hanger arms 35 carry a second b ar 34a at a height above the bai' 34 suicient to permit entrance between them of the extremities of the arms 32, The bar 34a has an inclined under surface located where it will be engaged by the key lever arm 32, when the key is fully depressed, and be then displaced so as to hold the latch bar 34 clear of the key lever arms. Such cooperation of any key lever arm 32 with the bar 33a continues until the corresponding key is released after being depressed and insures opportunity for a previously latched key lever to return into normal position before the latch bar returns into latching position. But the latch is returned by its spring 3l into arresting relation to the key lever last operated as soon as the key is released by removal of the operators finger from it.

An electromagnet ll is connected in circuit with a source of electric energy, indicated in Fig. 4 as a battery cl, and with a switch or circuit closer t8. This magnet serves to operate the printing attachment and to open its own circuit after so operating. The switch is normally open, having an arm 49 carrying one contact, which is spring biased so as to separate from the complemen'tal contact, For closing the switch there is provided a loosely pendent lever arm 5u carried pivot-ally by a lever 5i pivotcd at 52 to a fixed part of the framing or supporting structure (not shown). A spring 53 reacting between a part of the carrier lever 5l and the pendent arm E holds the latter against the extremity of the switch arm 4S and causes it to swing over the upper side of such extremity when raised. An extension on the lower extremity of arm 55 limi-ts its movement in that direction by coming to bear against the end of switch arm The carrier lever 5i is i Lised preparatory to closing the switch by a ratchet wheel 5G with which a pawl element or tooth 55 on the carrier arm engages. Ratchet 54 .is secured to a shaft 56, which latter is rigidly connected coaxially with the gear i? phonograph disk lf3, extends through a central bore in the shaft 2l, wherein it has a rotative bearing. The ratchet wheel has as many teeth as the phonograph disk has Wave groups, and its teeth are relatedl to the pawl element 55 so as to raise the carrier lever as each such group passes the pick up needle, thereby placing the switch closing lever in operative position with the 'fst movement of the mechanism following depression of key. But closing of the switch is not effected until the carrier lever descends when the mechanism is arrested by one (any one) of the stop levers 2l.

lever l by a gear sector Si! on the lever and a pinion 5l loose on the shaft of the escape wheel,

with which latter it has a one way driving connec'tion by means of a pawl E2. Rise of lever 5| turns the pinion El without turning the escape wheel, but descent of lever 5l causes the escape wheel to turn, the rotation of which is retarded by the pallet. Such retardation is predetermined to prevent descent of the lever 5G far enough to close the switch before it is again lifted by a iollowing tooth of ratchet Eli. But. when the drum is arrested (at which time the phonograph disk and ratchet wheel are also arrested) timey is afforded for the switch to be closed.

The armature 5H of the magnet dais carried by a pivoted lever having an arm 52| by which the printing hammer t5 is carried. Closing of the switch le therefore causes t'he hammer to press the paper and inked ribbon against the type wheel and make an imprint. An extension 531 of the armature lever pro'trudes so that its path crosses a cam portion of an arm 55a forming part oi the switch closer 56 wherefore the movement imparted to the extension 53| by the magnet displaces the switch closer and allows the switch to open by its own spring action.

Thus the circuit is closed whenever the movement of the type wheel is arrested, and opened as soon as printing has been effected. The operator is informed by visible or audible evidence of the operation of this printing attachment when the next letter of the message may be transmitted by depression of another key. He may not depress such other key until the printing attachment is operated in response to the action of the key last previously depressed, because to do so would cause failure to record the last transmitted letter at the receiving station. It is within our contemplation to provide automatic means under control of the magnet or its armature lever for preventing actuation of a key until after the printing attachment has operated, as by blocking the latch bar 3i so that it cannot release the key levers; but we regard such automatic obstruction as nonessential in View of the definite indi-cation given to the senses oi the operator by the printing attachment in its movement. The delay of such movement caused by the retarding escapement 58, 5e gives time for operation of the recording printer at the receiving station,

A lever 51M, which we call a synchronizing stop lever, is provided to correlate the type wheel of the recording instrument (later described) at the receiving station with the type wheel of the sending instrument. This lever is connected to the shaft 25 beside the end of drum 23 by means of a pin 55! so that it may swing in two directions, i. e., about the axis of the shaft and toward and away from the adjacent end of the drum. It has a short arm 55! arranged to coact with a synchronizing stop 57| on the adjacent end of the drum and a finger or blade 58! arrange to engage the threads of a screw or worm 59| on shaft 2l. A spring 63 is connected to this lever tending to hold the blade in engagement with the screw, and a spring 55 acts on the lever with tendency to withdraw the arm 55| from the synchronizing stop 5H. Preferably a single spring is used in practice for these purposes, arranged to act approximately on the line of the resultant of the forces exerted by the

springs

63 and 54, but for convenience of illustration in diagrammatic drawings such as these, we have shown two springs. It is within the skill of the machine designer to mount properly the above described equivalent single spring. The synchronizing lever has a cam or wedge portion 64| with which cooperates the extension of an arm 65| connected to the nearer one Vof the suspension arms or hangers 35 which carry the latch bar. The arrangement of these parts is such, as shown in Fig. 4, that when any key is depressed, the consequent movement of the latch bar causes arm to displace the synchronizing lever from engagement with the screw 5SH, whereupon the arm 561 is withdrawn from the synchronizing stop 5?! and the drum is left free to be rotated.

The stop lever may be so displaced, not only by the regular keys, but also by a special key 65, which we call a synchronizing key, carried by a key lever 65 which is like any other key lever except that it has no means for actuating a stop lever 21 and is not coupled to any such lever. But it has a rear arm 32| which, when the key is depressed, causes the latch 34 to be displaced and the synchronizing lever disengaged as just described. When the latch returns to normal position, the stop lever is permitted to engage the screw 5SH at a point axially removed to the right (with respect to Fig. 3) from its point of previous engagement, whereby rotation of the drum feeds the lever back toward its arresting position. In this embodiment such displacement is equal to the lead of two turns of the screw so that the drum may rotate, before being arrested by the stop lever, through an angle enough greater than one complete turn to insure placementJ of the type wheel of the receiving instrument in zero or starting position from whatever position it may have been left in at the end of a previous message. A suitably located stop pin or shoulder (not shown) limits the displacement of the stop lever to the distance above mentioned.

The displacement of the synchronizing stop lever similarly caused by operation of the regular type keys ensures against interference by the synchronizing stop with the rotation of the drum in sending a message. The greatest angular movement of the drum between any two stopping positions controlled by the levers 2 and stops 38 is less than one complete rotation, which is insufficient to cause return of the synchronizing stop lever into obstructing position.

The signal disk i4 turns at a high rratio with respect to the type wheel, which is here represented as being 6 to 1 but may be of othersuitable value. Thus a conveniently small phonograph disk having a conveniently small number of wave groups may be used with a type wheel having a large number of characters. There are as many wave groups as the number of characters on the typ-e wheel divided by the speed ratio, and the several wave groups are spaced proportionaly to the spacing of the characters on the type wheel. As the motor is regulated to run at an exact speed, the electrical waves or modulations generated by each group on the disk have the same frequencies as those produced by all other groups, whereby an impulse effect is produced, with the traverse of each wave group past the needle, at whatever receiving station is tuned to the frequencies of these wave groups.

An apparatus for recording the messages sent by the sending apparatus just described is shown in Figs. 6 and 7. This apparatus includes a type wheel 51 which contains exactly the same char-V acters in the same number and sequence as the characters of the type wheel 22. It is driven by a prime mover 68, which may be a spring or electric motor, capable of starting instantly and of driving the type wheel and other parts of the instrument at a suiliciently rapid rate; i. e., enough faster than the corresponding parts of the sending instrument to compensate for the intermittent movement presently described. The motor is coupled by gearing 69, il) with a let off or escape wheel and the latter is geared to the type wheel 6'! by a gear train T2, i3, M, 'l5 and shaft '16. The let off wheel has teeth equal in number to the number of wave groups on the sending disk le; and the speed ratio between this wheel and the type wheel 6l is equal to the speed ratio between the sending disk |15 and the type wheel 22 of the sending apparatus. The winding of an electromagnet 'H is coupled to a source of electric power under control of the tuned receiver whereby it receives a current irnpulse whenever an electrical wave group is generated by the sending disk. The armature '8 of this magnet is carried by a pawl lever 'i9 which is connected by a link 89 with a lever S2 which carries a pawl 8i. The two pawls are at diametrically opposite sides of the escape wheel and separated from one another by a distance so 1e lated to the wheel teeth that, when either pawl is displaced clear of the wheel the other pawl is in a notch between two teeth. A spring 83 is connected to this pawl assemblage normally tending, and eiective when the magnet is deenergized, to hold the pawl 8| clear of the wheel and the pawl 'le in a notch between two teeth. But when the magnet is energized the pawl 79 is disengaged and the pawl 8| brought into engagement with the wheel. The pawl 8| is mounted on the lever i with provision for movement tangentially of the wheel a distance substantially equal to the tooth spacing by means of pins 54 passing through slots in the pawl, and a spring 85 is connected with the pawl and lever in a manner to hold the pavvl at the limit ci its motion in the direction opposite to that of the adjacent side of the wheel. Thus the pawl is able to yield under the pressure of the motor driven wheel when brought into the path of any of the teeth thereof enough to permit rotation through the whole angle between adjacent teeth when pawl 'E9 is withdrawn.

A printing mechanism is provided beside the type wheel consisting of a paper tape SS, an inked ribbon 8l and a hammer (i8 carried by a lever 99, one arm of which carries the armature 9G of an electrcmagnet 9|, and is acted on by a spring 92 arranged to withdraw the armature from the magnet. This mechanism is substantially like that rdescribed in connection with the sending machine. It may be understood without illustration that we employ in the oommercial instruments, both the sending and receiving instruments, known means for propelling the paper tape after each impression a distance sufcient to avoid over printing of one character on another.

The winding of the magnet di is connected in circuit with a source oi power, represented as a battery 93, and with a switch 9d. Said switch includes a spring biased arm carrying one electrode and tending constantly to separate said electrode from the complemental electrode. It is controlled b-y a lever 99 pivoted at 99 and carrying a pivoted pendent lever |98 (like the lever 5i) of the sending instrument) lproject-ingtoward the switch arm 96 and closing the switch when lowered by descent, after rise, of the carrier lever. This lever has an upper bent arm 892 cooperating with an extension 89| on the armature lever 39 as in the sending instrument. Gravity and a spring 98| tend to lower lever 98. The pawl lever 82 extends toward lever 99 in such `proximity to a cam protuberance on the under side of the latter that, when moved by the magnet TI, as described, it engages this protuberance to prevent switch-closing descent of the lever. The switch controlling lever has a gear sector |02 meshing with a pinion |93 which is loosely rotatable on the shaft of an escape wheel |05 and has a one way driving connection therewith by a pawl m with the escape wheel |95. A pallet i cooperates with the escape wheel. Rise of the sector turns the pinion without affecting the escape wheel, but descent of the sector turns the escape wheel by means of the pawl and its rotation is retarded by the pallet.

A ratchet wheel |01 is connected rigidly with the let off wheel 'Il to turn at the same speed therewith and has the same number of teeth, but its teeth are inclined in the opposite direction so that they act as cam elements. They are arranged to coact with a pawl tooth |68 on the lever 98 so as to raise the latter whenever a tooth on the let oi wheel is allowed to escape past the pawl 18. The rise of lever 98 thus effected is sufficient to raise the switch closing lever I 60 so that the step on its end which closes the switch 94 is above the spring arm 95 in position to close the switch with subsequent descent of the arm. At each movement of the connected pawls to the left (with respect to Fig. '7) the arm 82 is brought under protuberance (1| While this arm and cam protuberance would sufce to raise the lever with each impulse of the magnet, we prefer to use the power of the driving motor through the cam ratchet |01 for that purpose -rather than to impose this burden on the magnet. But the protuberance may assist or supplement the cam ratchet in holding the lever in raised position. The delay caused by the retarding escape wheel prevents closing of the switch during the normal period between impulses when two or more are sent in succession, preventing the switch from being closed until the let off mechanism pauses after cessation of impulses due to arrest of the sending instrument by the means previously described.

The recorder also includes a synchronizing lever m9 pivoted transversely to a supporting shaft i9 by a pin and having a stop arm ||2 cooperating with a synchronizing stop H3 on the type Wheel, a iingerror blade cooperating with a screw H5 on the printing wheel shaft l, and a long arm terminating in a cam face beside a projection H5 on the armature lever. A spring ||1 holds linger |13 inengagement with the screw and permits disengagement therefrom by the action of `pin H6 when the printing magnet is energized. A spring 8 swings the lever aside about the pivot and withdraws the arm l2 from the stop I I3 or an equivalent single spring operating on the resultant line of the efforts of these two springs may be used. Each actuation of the printing magnet releases the synchronizing lever and causes it to re-engage the screw at a point far enough removed from stop ||3 to permit at least one rotation of the Vtype wheel, but not so extensive a rotation as that permitted the drum of the sending instrument Vwhen its synchronizing stop is released. Thus the printing of the last character of a message leaves this type wheel free to be automatically correlated with the type wheel of the sending instrument.

In this disclosure of signal sending and recording means we have not attempted to show details of framing, bearings and other supporting means for the moving and stationary parts, but have contented ourselves with a description of the principles of the machines and a diagrammatic illustration of their parts and an operative relationship between such parts in as simple a manner as possible and with the least possible number of drawings. This showing is sufficient for an understanding of the invention and to enable draftsmen and mechanics, using the common knowledge and skill oi their respective callings to design and build operative oommercial machines.

In order that a message may be correctly transmitted by the instruments here described, they must be in correct correlation or coordination with each other. Normally they are so related, particularly where in frequent use, for the conclusion of one message leaves them in correct positions for sending the next one. But in case they are not, or if the operator wishes to avoid any possibility of their being out of step, he depresses `the synchronizing key 65 of the sending instrument before sending the message. releases the synchronizing stop 57| without imposing any other stop in the path of the drum, and at the same time causes displacement oi any stop lever 27 which may previously have been in the path of a stop 3B. The drum and sending disk I4 then rotate and a succession of equally timed wave groups is transmitted, causing the type wheel of the recording instrument to be rotated step by step at the same average rate as the continuously rotating type wheel of the sending instrument. The synchronizing levers of both instruments are simultaneousiy fed by their screws toward the arrestinfr position; and that of the receiving instrument, having a shorter distance to go, reaches its arresting position iirst. The rotating parts of the sending instrument, however, continue until similarly arrested. The type wheels of both instruments then are in correlated zero position; in other words, corresponding characters of both are registered with the respective printing hammers.

A message is sent by the operator striking the keys 24 in the same manner as one would the keys of a typewriter. The rst key displaces the latch bar 34, releasing the synchronizing key and synchronizing lever, (or, if the synchronizing key had not been just previously depressed, then the key corresponding to the last character of the last previous message), and placing itsl associated stop lever 2l in the path of a stop corresponding to the letter or character to which the now de-.

pressed key is appropriated. The sending disk rotates through a proportional angle, transmitting a number of Wave groups, equal to the number of characters on the type wheel in an angle equal to that between the stop lever 2'! and the nearest stop 38 in the same zone. The resultant impulses received in the tuned receiving station cause an equal angular movement of the type wheel of that station. When the wheels of both instruments then pause, the switch closing levers of both, which have meanwhile been maintained in raised position by the lifting ratchets and retarding escapements, descend and close the switches 48 and Elfi. A printing impression is This Y made at both stations and the switches are simultaneously opened.

The retarding escapements here shown are of well known character and are capable of being adjusted as to their timing function so as to permit descent of both carrier levers 5i and 98 at the same rate or at different rates as desired. If necessary to insure that each character will `be printed at the receiving station before another series of impulses are generated at the sending station, the retarding escapement of the sending instrument may be adjusted for greater delay than that of the receiving station. But ordinarily this is unnecessary.

In the operation of the let off device of the receiving instrument, withdrawal of lpawl 7S from the ratchet wheel brings pawl 8l into a vtooth space at the opposite side and allows the wheel to turn through the full spacing of one tooth immediately. When the armature is released, pawl 'I9 enters the next tooth space while pawl BI is withdrawn (by the action of spring 83) but the wheel does not rotate. Pawl 8|, as soon as released from the ratchet wheel, is raised by its spring 85 ready for re-engagement with the wheel. With each wave impulse, the ratchet -wheel turns one step and waits for the next ima repetition of the action thus described. As all the stops in any one zone of the sending instrument drum are equally correlated angularly with the same number or letter on the type wheel, when two or more sets of characters are -provided 0n the wheel, it is immaterial whether the drum turns througha large or a small angle before being arrested. In any case the character corresponding to the key depressed is placed in printing position when the drum is arrested, and

a number of impulses corresponding to the angle of rotation is transmitted to the recording instrument, causing the type Wheel of the latter to be turned through an equal angle.

At the conclusion of the message both type wheels are left in the last printing position and, so long as both remain in corresponding positions, a further message may be sent and correctly received without employment of the synchronizing means herein described. Such synchronizing means, however, overcomes any liability of failure to record the received message f correctly due to displacement of the recording type wheel'unknown to the sender.

The signal transmission by the instruments just described is eiected by impulses of equal duration, equally spaced in point of time, the number of which is equal to the number of spaces on the type wheels between successiveA letters or symbols of the message. rIhese impulses are translated at the receiving station into a printed record the same as the message transmitted. Where the characters are jumbled, and particularly when two or more series of characters are provided and those of one or more sets are arranged out of their conventional order, the nurnber of impulses between pauses affords no logical guide for decoding the message in case it is intercepted by an interloping receiver. But the correlated receiving instrument automatically decodes the message transmitted with the aid of such jumbled characters.

The transmitted message is receivable only at a station or stations provided with selectors tuned to the frequencies of the wave groups generated by the sending phonograph disk. But the same instrument may be used for sending to different receiving stations by the mere substitution of different disks having recorded tone group frequencies to which the different stations are tuned. In order to make interception more diilicult, the tone groups of the sending instrument may be augmented by one or more idle tones which are not intended to affect the receiving instruments, but will confuse a spy.

The type wheel of the sending instrument is not essential for the transmission of messages because the drum, or its equivalent, is the controlling element which determines thenurnbern of impulses generated at each stage of transmission. But the type wheel and printing attachment here are desirable as they cause a record to be made at the same time the message is sent, which may be useful as a check on the accuracy of the rnes- Sage received.

The speed of message sending is limited by the time required for operating the relays at the receiving station, which time is in the order of 1/60 of a second. Hence approximately 60 impulses may be transmitted per second and the control disk is geared to rotate at a corresponding rate, or slower if desired.

The tones produces by the wave groups transmitted with this rapidity and for correspondingly short periods of time, cause noperceptible interference with words or music broadcast at the same time by means of a radio wave of the same frequency as that used for signal transmission, since their duration is too short to have any disturbing effect on the ear of the listener. Hence our system may be used by employment of the same radio frequencies used for other purposes, and on telephone lines used at the same time for conversations.

The principles of means for selectively and exclusively activating different receiving stations and recorders are more fully illustrated in Fig. 8. This illustrative system is controlled by six different tones used three at a time. For convenience the tones will be referred to as l, 2, 3, 4, 5 and 6, which may be of any consecutive or nonconsecutive pitches, but all different from one another, The reference characters here used are the same as in the general diagram of Fig. l, modified by exponents related to the several tones. OJ-b represents the tone generator and signal sender, such as that illustrated in Figs. 3 and 4. d is the transmitter of standard character, and c an amplifier which is usually necessary but not an essential factor of the invention. f is the receiver of standard character and s is a power source such as a battery or generator capable of furnishing sufficient energy to operate the recording instrument of Figs. 6 and 7 or other recorders. g1 is a selector tuned to the tone l by selective means such as the network shown in Fig. 2 or equivalent means. Its input side is connected to the receiver and its output side to a relay 1L11 sufficiently sensitive to close a switch in the,` power circuit from the power source s when traversed by the signal transmitting vibrations. g2, g3, g4, g5 and g6 are similar selectors tuned to the

tones

2, 3, 4, 5 and 6 respectively. Selector g2 is connected with relay b21 and selector g3 with relay 1131. The several recorders are located in the column beneath the reference4 letter i, distinguished4 from one another by numbers designating the tene groups which control their operation.

Assuming that the signal generator produces simultaneously the tones l, 2 and 3, then through the selectors g1, g2 and 93, the relays 1111, h21 and 1131 are simultaneously operated and a circuit is made through the recorder bearing the number 123. In like manner the selector g4 is connected with relay h11 whereby, if the tone group consists of tones l, 2 and 4, the recorder at E24 is actuated. Selector g5 is similarly connected with relay 1151 and Q6 with relay 1161, whereby the tone 4 or tone 5 substituted for tone 3 of the tone group causes actuation of the recorder 25 or 26 respectively.

A second relay 1222 is coupled with the selector g2. Other relays, designated by the letter 1L with appropriate exponents are similarly coupled to the selectors g3, g4, g5 and Q6, and connected in circuit as shown by the diagram So as to cause operation of the different recorders each by its own appropriate tone group.

To avoid duplication, all of the twenty record ers represented are shown in the diagram as connected by wiring with thirty-four relays and six selectors, all receiving impulses from a single receiver and power from a single power source. Eut it is to be understood that where the syscomprises stations separated from one another in space, each station will consist of one recorder with its own receiver, power source7 three selectors and three relays. Any such recorder is operable by vibration frequencies to which its selectors are tuned carried by a radio wave to which its receiver is tunedy provided the impulses so received are powerful enough to operate its relays.

Where a number of recorders may be located in the same place, as in a re engine station to record alarms sent from scattered boxes, mechanically coupled plural switches may be operated by the relays to close one gap in the circuits of all the recorders which are affected by the same tone. Thus, referring to Fig. 9 which illus trates a simple system controlled by six tones, the conductors t1 and t2 represent connections from the receiver to all of the tuned selectors g1 to 9'1 inclusive. Relay h1, controlled by the selector g1 is connected to close a circuit between the conduc-tors u1 and u2 from a power Source s, in which is included the magnet of a switch v1. Similarly each of the other selectors and relays is connected to operate one of the switches o2 to o6 inclusive. The switch o1 is adapted to open and close a switch contact U11 in all of the recorder circuits associated with tone 1. rlhe switch o2 operates circuit closer U21 in circuit with all the recorders controlled by both tone l and tone 2; and circuit closer 1:22 in all the other recorder circuits controlled by tone 2. In similar fashion the other switches control circuit closers in the circuits of the several recorders, as will be cle-ar from the diagram. Each of the fire alarm boxes or other transmitters corresponding to the recorders herein indicated by the oblong outlines bearing three-digit numerals, generates a group of three tones which is imposed on a radio wave. The group of tones for each box is different and distinctive but the radio wave length and frequency for all is the same. Each box therefore, when operated, causes the appropriate one of the recorders at the central station to record or indicate its operation.

It may be remarked that for the purposes of j this invention andthe. genericA protection sought,

we make no distinction between a recorder and an indicator, considering thata recorder is an indicator also and that one is the equivalent of the other.

In the foregoing description it has been assumed that the tones generated at the transmitting station are produced simultaneously. Where the tones are generated progressively, and may be so generated in any order, the number of possible stations in a system using a given number of tones is factorial G times the number of stations possible with tone groups generated simultaneously, where G is the number of tones used in the group. In Fig. l We show how, by the employment of auxiliary switches, different stations, each controlled by the same three tones, may be selected exclusively by those tones when produced in different sequences. As in the preceding gure, t1 and t2 represent the conductors of the output circuit from the receiver; u1 and u2 represent the line wires from a power source; g1 to g6 inclusive represent selectors tuned to the respective tones; and h1 to h6 inclusive designate therelays associated with the several selectors. Let it be assumed that the tone group consisting of the

tones

1, 2 and 3 generated in that order is received at the receiving station. The electrical vibrations corresponding to tone 1 then operate the relay h1 to close a circuit between the lines u1 and u2 in which is included a relay switch ull. This switch then closes a gap in the magnet circuit of switch 'U21 which is in circuit with the switch of the relay h2. When tone 2 comes to the receiver this circuit is completed and the switch 'U21 then closes a gap in a circuit which includes the magnet of switch D31 and relay h3; whereby, when tone 3 comes into the receiver all three switches '011, U21 and U31 are closed between the power lines and the recorder or indicator 23. It is necessary that tone 1 persist until

tones

2 and 3 are received and that tone 2 persist until tone 3 is received. There must be an overlapping of the three tones for a time long enough to cause operation of the recorder. The production of these tones in sequence causes one impulse to be generated at the recorder, such as the activation of magnet 'il in Figs. 6 and '7.

If the tone sequence is 2-1-3, for instance, the switch '026 is rst closed, causing the switch 2212 to be closed when tone 1 is received and switch 'U36 to be closed when tone3 is received, completing the operating circuit for the recorder 213. Similarly the same three tones in the order 3-2-1 cause iirst the switch 12311 then the switch 1128 and finally the switch 1118 to be closed in succession, operating the recorder 32|.

The relays responsive to other tones are connected with switches in essentially the same manner to operate the indicators at 120 different stations by diiferent groups and sequences of three tones each. The connections for approximately half of these stations are shown in Fig. l0. A suitable extension of the diagram to include the whole series will be readily apparent to those skilled in the art. In this case, as in Fig. 8, the stations havebeen grouped together to save space and avoid duplication of selectors and relays. But in actual practice each station may be widely separated and spaced from all others and contain its own three selectors, relays and sequence switches.

The same principles are capable of indefinite extension with the use of a greater number of tones, while stations may be made more selective by using more than three tones in their controlling tone groups. Equivalents of the several means and instrumentalities hereinbefore described are included within the scope of the protection herein claimed, such as other means of vibration generation or tone production than the phonograph disk herein illustrated; other means of indicating or recording than the type wheel illustrated, such as interruptions producing dot and dash signals and a marker for printing such signals. And any suitable radio or telephone equipment may be used for transmitting and receiving the tone frequencies.

The word tone in this description is used as indicating Vibrations, Whether audible or not, which have a definite frequency, whether such frequency is that of a musical note of the standard scale or an inharmonious frequency.

What we nclaim and desire to secure by Letters Patent is:

1. The method of communication which consists in generating periodically a group of vibrations of different frequencies like or analogous to a chord of tones, each period consisting of a limited time during which such Vibrations are generated and a time during which no vibrations are generated, causing such periodic generation to cease at the conclusions of diiferent numbers of periods in accordance with a signal code, transmitting such vibrations electrically, transforming the vibrations into mechanical motion at a receiving station by power under the control of a plurality of receivers each tuned to the vibrations of one particular frequency, and causing the movements so resulting from the transformed received vibrations to produce periodic impulses Y correlated with the generation of such group of vibrations.

2, The method of communication which consists in modulating a radio carrier wave by a plurality of vibrations of respectively diierent prescribed frequencies with overlapping of the persistence of such vibrations of different frequencies in point of time, generating such modulating vibrations periodically with persistence during brief periods of time and intervals between successive generations, sending signals by so producing such modulating vibrations in numbers of periods according to a code, receiving the modulating vibrations in different selectors, each tuned to vibrations of a specific frequency, at a receiving station, combining and transforming the received electrical vibrations of different frequencies into a mechanical impulse with each period of received vibrations, and causing the successive impulses so produced toreproduce the message transmitted from'the sending station.

3. The method of communication which consists in producing periodically at a sending station a group of vibrations of different frequencies, one at a time with persistence of the vibrations of each frequency until all those of the group, have been generated, transmitting such vibrations electrically to a receiving station, causing the vibrations of each frequency to operate a selector tuned to that frequency at the receiving station, and causing the vibrations of one frequency first received to control the effect produced by subsequently received vibrations of a different frequency.

4. A communication system comprising an apparatus for mechanically generating groups of respectively different vibrations with an interval after each group, means for controlling the ac.

tion of said generating means to cause generation of different numbers of successive groups in accordance with a prescribed signal code, a transmitter having means for transforming such mechanical vibrations into electrical undulations, a receiving station having selectors tuned individually to the different vibrations of such group, a source of electrical energy, relay switches in the circuit of said source, each under control of one of said selectors, a motive apparatus in circuit with said source adapted to produce a mechanical impulse when said relay switches are closed, a signal instrument, and means operated by said motive apparatus for propelling said signal instrument through a number of successive steps equal to the number of vibration groups generated with each action of said generating means.

5. A communication system comprising a mechanical generator of vibrations having means for producing in regular periodic succession a group of vibrations of respectively different frequencies with intervals between successive groups, means under the control of an operator for actuating said generator to produce a greater or less number of such groups in continuous succession and to intermit such vibration production at the end of a prescribed succession of groups, an electrical transmitter for transforming and transmitting said groups of vibrations, a receiver of electrical vibrations, a plurality of selectors associated with said receiver and each tuned to pass vibrations of a given frequency different from the frequency to which another of said selectors is tuned, relays each separately operable by one of said selectors, a power source in circuit with said relays, means connected for operation by said power source and adapted to produce a single impulse of mechanical motion when all of said relays are energized at the same time by vibrations passing through their respective selectors, an indicating instrument movable through successive steps of movement, and means for causing each said impulse to move the said instrument through one of said steps.

6. A communication system comprising a generator of vibrations having means for producing vibrations of respectively different frequencies in successive groups, with the vibrations of one frequency in each group preceding and overlapping the generation of the other vibrations of the same group, and repeating such groups of vibrations with intervals between them, means for propelling said generator and arresting its action under control of an operator after production of one or more groups of vibrations, a transmitter having means for converting such vibrations into electrica-l vibrations, a receiver of electrical vibrations, a plurality of selectors each tuned to vibrations of a specic frequency diierent from that to which another selector is tuned, a source of electrical energy, an indicator instrument and a normally open switch therefor in circuit with said source of energy, means operable by one of said selectors for closing said switch, and means operable by another selector for preventing -actuation of the last named means except when such other selector is energized.

7. In a communication system, a receiver of electrical vibrations responsive to a range of vibration frequencies, a plurality of selectors connected to said receiver each tuned to pass vibrations of a frequency within said range and different from the frequency which the other selector can pass, a source of electrical energy, an electrically operated indicator, a'normally open relay switch between said indicator and the power source, a normally open relay circuit closable by one of said lselectors for actuating the indicator relay, a normally open relay switch in the circuit between the power source and the said selectoroperated relay circuit, and means controlled by another selector for closing the last named switch, whereby actuation of the indicator is made possible only when said selectors are energized in a predetermined order.

NATHAN H. SUREN. WILLIAM W. CARTER.