US2463236A - Secret telegraph system - Google Patents

Description

arch l, 1949. w M BACON SECRET TELEGRAPH SYSTEM Filed March 9, 194e 2 Sheets-Sheet 1 @m 0C WA WS A W S .v2

T w E: l, wg Fu" lv IS @Tx 2 sheets-shet 2 March l, 1949. w. M. BACON SECRET TELEGRAPH SYSTEM Filed March 9, 1946 NVENTOR W 'M BACON @y ATTORNEY Patented Mar. 1, 1949 NITED HCE SECRET TELEGRAPH SYSTEM Application March 9, 1946, Serial No. 653,256

6 Claims.

This invention relates to telegraph systems and more particularly to secret telegraph systems.

In telegraph systems, messages are transmitted and received in any well-known code and when intercepted in this condition, during the course of transmission, are intelligible to anyone skilled in the art. However, in secret telegraph systems the message signals are altered for transmission over the line and when intercepted in their altered form are unintelligible.

At the transmitting end of a secret system, these intelligible messages prepared at the transmitter are, before being impressed on the line, enciphered by means of other signals of what is generally known as a key code and the enciphered messages with their altered signals are transmitted over a line so that any interception on the line will cause to be received by the interceptor unintelligible messages. At the final receiving end these unintelligible messages are deciphered lby means of other signals identical with those of the key code at the transmitting end and the deciphered messages are recorded to produce the messages as originally prepared.

Heretofore in secret telegraph systems diiculties were experienced in developing a completely shielded device for transmitting messages to the enciphering set or for receiving messages from the deciphering set for recordation. At the sending end Where the transmitting device may be a keyboard or an automatic tape transmitter or a transmitting relay of a sending teletypewriter, or at the receiving end where the receiving device may be a line relay or a repeating relay or the selector magnet of a receiving teletypewriter, it has been found that each device upon the make or break of its operating contacts radiates a short, sharp Voltage pulse. These pulses when radiated in a location which is comparatively free from other electrical disturbances and in which a ciphering or deciphering set is operated, may be surreptitiously or otherwise received, or picked up, by a radio receiving device located in an adjacent room or within some other short distance or at a vmuch greater distance along a power or signal wire which is connected to or passed close by the set, and recorded as pulses by an oscillograph. From these pulses appearing on an oscillogram can be constructed the signals of the complete message as originally prepared.

An object of the present invention is to protect a secret message from detection at any point between the point of transmission and its associated enciphering set and at any point between a deciphering set and its associated receiving teletypewriter by masking short, sharp voltage pulses picked up from a transmitted message with other pulses so as to produce on an oscillogram, a pattern of voltage pulses that is uniform for all code combinations in the transmitted message.

According to the present invention an arrangement is provided in connection with a transmitting or a receiving teletypewriter for masking the short, sharp voltage pulses which are radiated from the circuit of the message signal repeating, or relaying, element at times corresponding to the transitions of the plain text signals constituting the secret message, by adding other short, sharp voltage pulses radiate-d from a similar element in a dummy circuit controlled by the plain text signal and having the same electrical characteristics as the circuit of the message signal repeating element. The pulses radiated from both circuits, if received by a radio receiving set located in proximity to the teletypewriter for producing an oscillogram of the combined voltage pulses radiated by both circuits will be arranged in a pattern that is uniform for al1 code combinations.

A feature of the invention is the provision of means for producing a series of voltage pulses, one for each of the possible transitions in a transmitted signal code combination so as to show on an oscillogram a uniform pattern for all the code combinations of a transmitted message.

Another feature is the provision of means for closing either the plain text signal circuit or the dummy circuit at each of the possible transitions in each of the message signal combinations to produce an oscillogram showing a pattern of Voltage pulses that is uniform for all code combinations, that is, each series of pulses will have the same pattern for all signal combiy nations in the start-stop permutation code.

Another feature is the provision at the sending and/or the receiving end of the system, of a dummy circuit having electrical characteristics identical with those of the plain text signal circuit, the dummy circuit including a repeating relay or operating magnet identical with that of the plain text signal circuit, and two groups of contact sets which jointly function to operate either of the corresponding relays or magnets in response to each of the selecting pulses of each signal combination transmitted or received. The contact sets of one group are respectively operated by the code bars to either their marking or spacing positions in correspondence with the positions of those bars. The contact sets of the other group are controlled by the cams on the transmitting cam shaft. One contact set of the group controlled by the cams on the transmitting cam shaft is normally closed but arranged to open as soon as the cam shaft rotates out of its stop, or normal, position and remain open until the cam shaft again reaches its stop position at the end of a revolution. The other contact sets of the group controlled by the cams, which respec.. tively correspond to the selecting pulses, are normally open, but are arranged to momentarily close successively once during each revolution of the cam shaft. The printer selector magnet is normally operated inasmuch as it is under the sole control of the contact set which is always closed when the cam shaft is in its stop position and is arranged to release as soon as the cam shaft rotates out of its stop position. It will operate only at such other times during a revolution of the cam shaft as the normally open contact sets corresponding to the selecting pulses and controlled by the cam shaft, are closed and their respectively associated code bar contact sets are in their marking positions. The other magnet, which is in the dummy circuit, is normally in a released condition and is operated only at such times during a revolution of the shaft, as the above-mentioned normally open contact sets are closed and their respectively associated code bar contact sets are in their spacing positions.

Another feature is the provision on a teletypewriter of a rotatable cam shaft having cams arranged to successively close the Contact sets respectively corresponding to the selecting pulses of a signal combination. Certain of these closed sets may, depending on the signal combination being transmitted, be included in the operating circuit of the selector magnet to effect its operation in response to each marking pulse and the others may be included in the operating circuit of the dummy magnet t effect the operation of the dummy magnet in response to each spacing pulse, the interval of closure of each pair of contacts being approximately 90 per cent of the duration of the regular interval of a selecting pulse.

The invention will be better understood by reference to the following detailed description taken in connection with the accompanying drawings in which:

Fig. 1 shows the invention in connection with the transmitting end of a teletypewriter system wherein the teletypewriter is provided with transmitting contact sets arranged to close an operating circuit for the printer selector magnet or transmitting relay in response to each marking selecting pulse of a signal combination to be transmitted from the teletypewriter and to close an operating circuit of a dummy magnet or relay for each spacing selecting pulse, the operating circuit for the dummy magnet having electrical characteristics identical with those of the printer selector magnet circuit. The teletypewriter is shown as a part of a schematic circuit instead of as a part of the actual apparatus.

Fig. 1A represents a superimposed'arrangement of the cams on ya start-stop rotatable shaft replacing the regular transmitting cam shaft of a teletypewriter for the purposes of the present in- Vention.

Fig. 1B shows an end elevation view of a rotatable transmitting cam shaft assembly as modied in accordance with the present invention.

Fig. 1C is a diagrammatic showing of a plain text signal Wave for the letter I in start-stop fiveunit permutation code and its effect on both the plain text signal circuit and the dummy circuit of the circuit arrangement illustrated in Fig. 1.

The present invention will be described as applied to the transmitting end of a secret teletypewriter system, it being understood that the invention adapted for operation at the receiving end, will be obvious from the description herein given.

The signal code used herein for transmission is the start-stop, five-unit permutation code which comprises ve selecting pulses used in various combinations of current and no current intervals, namely, mark and space, depending upon the signal transmitted. Each group of five selecting pulses is preceded by a start, or space, pulse and followed by a stop, or mark, pulse, the latter being used to maintain synchronism between the Stations in the system. The mark pulses operate the printer selector magnet of a teletypewriter and are known as markingf and the space or non-operative pulses which cause it to release, are known as Vspacing The use of reference characters has been kept to a definite plan. Like parts have correspond.. ing reference characters with the addition of primary and secondary symbols in Figs. 1A and 1B respectively.

Referring to Fig. 1, the teletypewriter keyboard transmitter comprises a set of keys represented by key |00, key levers represented by levers |0|-|,' |0|.-2, and |0|-3, etc. which are maintained in normal position by springs |02|, |02-2 and |02-3, etc., a bank of contact springs |03 |0 32, |033, |03-4 and |03-5 in engageable relation with fixed terminals |04-|, |04-2, |043, |04-4, |04-5,respectively. Cams IUS-el, |05.-2, |05-3, |05-4, and |05-5 xedly mounted on rotatable shaft |06. Shaft |06 is arranged to be driven by driven clutch member |01 and driving clutch member |08 connected through a set of gears (not shown) to the main shaft of the printer unit which, in turn, is driven by a motor (also not shown). The teletypewriter employed herein may, with certain modifications hereinafter described, be of the type disclosed in U. S. Reissue Patent 20,330, granted to S. Morton on April 13,*1937. For example, what is referred to herein as a printer selector magnet |2| may actually be a repeating relay, such as relay (30), of an enciphering and deciphering device |31 disclosed in K. E. Fitch et al. U. S. Patent 2,405,571, dated Aug. 13, 1946. Other reference characters in parentheses shown in the drawings of the present application represent corresponding elements in K. E. Fitch et al. U. S. Patent 2,405,571. The cams together with start-stop cam |09 mounted on shaft |06 are normally held stationary because clutch members |01 and |08 are held apart by latch member ||0 which is normally in engagement with throw-out cam When a key, such as key |00, is momentarily depressed. universal bar H2 which is pivotally supported at each end by a pin, such as pin |i3, and extends beneath all the key levers, is momentarily operated in a counter-clockwise direction around pin I3 to move the free end of latch member ||0 in a clockwise direction around pin ||5 and against the tension of coil spring |l0. Latch member ||0, upon being rotated around pin 5 disengages at its free end throw-out cam I thereby permitting the driven clutch member |01 to mesh with the driving clutch member |08 to cause cam shaft |06 to rotate about its axis- At the end of one revolution of cam shaft |06, driven clutch member |01 is disengaged from the driving clutch member |08 by the throw-out cam again engaging latch member |0 and the cams on shaft |06 are brought to a stop and remain stationary until the keyboard is again operated. Beneath the key levers |0||, |0|-2, |0|-3, etc. are ve selector, or code, bars ||6-|, IIE-2, l |6-'-3, ||64 and ||6-5, and the front portion of the universal bar ||2, which extends across the width of the keyboard. The selector, or code, bars are provided with saw-toothed shaped notches arranged according to the requirements of the signal code. These bars rest on rollers (not shown) and are guided at each end so that they may be easily moved endwise. When a key is depressed, the key lever, striking the slanting sides of certain of these notches, will operate one or more of these bars either to the left or to the right depending upon whether the corresponding pulses of the signal combination are to be marking or spacing pulses as described in S. Morton U. S. Reissue Patent 20,330, supra.

Each of the selector, or code, bars has connected to its right end a bumper of insulative material. When each of the code bars ||6| to |6-5 is moved toward the right it causes its corresponding bumper of bumpers to |`|5 to actuate a contact spring member of those designated ||8| to ||85 into engagement with a contact member of those designated ||9| to IIB-5, and when moved toward the left withdraws its corresponding bumper to permit its associated spring member ||8 to engage its respectively associated contact member of those designated |20| to |20- 5. The contact spring members ||9 are in either of two positions, namely, in engagement with their respectively associated contact members ||9 or |20. When the contact spring members ||8| to l |8-5 are in engagement with their respectively associated contact members |20 each is prepared to send a mark pulse to selecting magnet |2| and when in engagement with their respectively associated contact members ||9| to ||95 each is prepared to send a space pulse to operate dummy magnet |22.

In connection with Fig. 1B reference may be had to H. L. Krum U. S. Patent 1,595,472, granted August 10, 1926, Fig. 2, for a detailed description of the arrangement for locking code bars I6 in their set positions until the transmitting cam shaft |06 completes a revolution after each teletypewriter key is operated. None of the keys except the one depressed can be operated until locking bar |45 is raised. Fig. 1B is substantially similar to Fig. 2 of S. Morton U. S. Reissue Patent 20,330, supra, except that the switch Shifters |30" do not latch during the time that transmitting cam shaft |06 is rotating through a revolution. The reference characters in Figs. 1 and 1B designate like parts.

Each of conductors |23| to |23--5 is connected at one end to its respective contact spring member of those designated ||8| to ||85 and at the opposite end to its respective terminal member of those designated |04| to |04-5. The marking contact members |20| to |20-5 are connected to a path extending over conductors |24, |25 and |45, through the winding of selector magnet |2| to grounded positive battery are connected to a path extending over conductor |21, through the winding of dummy magnet |22,

to grounded positive battery |26. The contact spring members |03| to |03--5 which are engageable with terminals |04| to |04-5, respectively, are connected to conductor |28 which extends to the grounded negative battery |29. Contact spring members |03| to' |03--5 are normally restrained from engaging terminals |04-l to |04-5, respectively, by means of gooseneck-shaped switch Shifters |30| to |30-5, respectively, the latter being pivotally supported on rod |3|. Switch Shifters |30| to |30-5, through their respective peak portions |32| to |32-5, are at all times in engagement as shown with cams |05| to |05-5, respectively. These peak portions may be considered as idlers in continuous engagement with cams |05.

Cams |05| to |05-5 have peripheral indents of the same angular distance, spirally arranged with respect to each other so as to follow successively, during the revolution of cam shaft |06, in passing the alignment of points on peak portions |32 whereat the cam indentations are successively engaged. The indentation on each of cams |05| to |05-5 subtends an angle about 10 per cent less than the angle subtended by an indentation on each of the selecting cams of a regular transmitting cam shaft of a teletypewriter such as shown in Mortons Reissue Patent 20,330, supra, so that each of the successive closures between contact members |03 and terminals |04 is of a duration slightly less by 10 per cent than the closure of a selecting pulse of the usual start-stop, five-unit permutation code. In other words, the circuit controlled by cams |05 is, during each revolution of shaft |06, opened for the usual start pulse and then successively closed for per cent of the duration of each of the next five pulses and closed again for the stop pulse.

In accordance with the above, start-stop cam |09 controls in a manner similar to that of cams |05| to |05-5 the restraint of gooseneckshaped switch shifter |33 over contact spring member |34 which is normally in engagement with terminal |35. Peak portion |36 of switch shifter |33 is at all times in engagement with start-stop cam |09 and normally maintains the contact between contact spring member |34 and terminal |35 closed in a circuit traceable from grounded negative battery |29, conductor |28, terminal |35, contact spring member |34, conductor |45, through the winding of selector magnet I2 to grounded positive battery |26, and therefore when the start-stop cam shaft |06 is stationary, the operating circuit for selector magnet |2| is closed to maintain the magnet operated. However, the normally closed contact between contact spring |34 and terminal |35 is opened at the beginning of each revolution of cam shaft |06 to thereby open the operating circuit for selector magnet |2| to send thereto a start, or spacing, signal and the magnet releases. Then cams |05- to |05-5, in turn, condition the operating circuit for the ve selecting pulses of the signal coni` bination. After the circuit is conditioned for the fifth selecting pulse, contacts of contact spring |34 and terminal |35 are again closed by start-stop cam |09 to close the circuit for the stop, or mark, pulse. The contact between contact spring member |34 and terminal |35 will remain closed until the keyboard is again operated, at which time the clutch driven member |01 will again be permitted to mesh with clutch driving member |08 to start cam shaft |06 through another revolution rhereicuyl conditioning-' the; circuit. for another;V sig:- nal'.

In the startstop; five' unit permutation code the pulses of. each signal are arranged" sothat the start, pulse. and eachi ofthe selecting; pulses Nos.` l to are of equall duration;that-.is;.unity; andv the stop: pulse is. 1.42 times longer.' This would meanA that each'. of thel sectorsres-pectively. corresponding; tov the'. start' pulse andI the ve select-ing pulses Would have any angular' width of 48;5.-| degrees and-thersector'correspondingto the; stopf pulse'. wouldY have'.v an angularv Width: of 68:9-I degrees as shownin Fig. 1A. HoWever',,ln order' to satisfy the requirements of thev present invention-special cams areprovided; in plac'ef of the regular selecting cams cnf the.' transmitting camshaft |06. Asjhereinbefore stated each.` of the selectingcams, Hit-I to'V I(l5- 5haslaniinden tation which is approximately" 90A per cent in angularrwidth of those provided onr theriselecting cams of. the'ordinary teletypewriter,.the indenta, tions provided on. cams, |V|l5l|f to |05-51 having an' angularxdistance' of 485+ degrees minus L8-IT degrees',or43;7- degrees Whichis 90per cent of theangularwidthgof the'in'dentation onztheure'gu' lar. selecting' cams.. This difference. of l'per'cent is divided into equal parts for application atthe beginningandthe ending of each' indentation. so that; all contacts.' controlled by` cams I05--III to M35i-5', as'. Well* as cam I 09. as hereinbefore'vr stated,` are openv at thei beginningand theending ofeach SeIeCtingpulSe o'f` everysignal combination. The reason, for decreasing 'the' angular 'Widthof the-indentations'on cams IOSL-I to IUS-5 isto provide orthe release of either the selector'magnet' |2'I aftereach^ pulse of a continuous series of marking pulses or'the dummy magneta'fter each pulse-of al continuous. seriesof spacing pulses'.

The contact spring members IIB are actuated by-'theirrespective code bars I-I 6 into'engagement with their respectively associated contacts IIB and! lsdependingfon- Whether the' corresponding selectingy pulse-oi the signal' combination is-'spac ing' or marking, and remain in such position until tliekeyboard is-againoperated. The' cam Shaft HE'v in making one revolution Will successively close'- the operating circuit for selector' magnet' |21 or dummyv magnet |22', the operatingcircuit selected for' closure depending; upon the position or'the corresponding' Contact spring member I'I8 they time'the closure iseiected by th'ecorresponding; cam but the' closure of the` particular circuit will be' for a duration of'only 90per cent of that' of' the regular selecting pulse,

As h'ereinbefore` stated, selectorr magnet I'TI mayserve' a's'the regular printer' selector'magnet' of a teletypewriter, or'as'a sending orl azrepeat'er relay' for' transmitting the plain text signalsl to' code` ciphering'set of device ISI'Wherein thesig; nai's of a key code are' superimposed; onth'e plain text.si'gnal for transmitting,unintelligible signals' over the line. With respect to the selecting pulsesofeaolicode combination, selector magnet I2'TI,` i's arranged.' to operate and release in response. toeach markingselecting pulse and' dummy mag,- net. |22 is arranged to operate and' release in response to each spacing, selecting pulse, of.' each signalcombinatiomwhereby a short voltage pulse is radiatedj by eitherv magnet atI every possible^ transitionrandeacli signal combination radiates avseries ofv pulses that forms a uniform pattern for. every' signal characterrtha't is` originallyV pre'- pared 'w segment: off start-stop' camv IUS" leaves'- the?peak'1 The-method. ofi operationvwill lnow; be; described withTv particular. reference to lig.` li-C whereinY a startfstop, 4five-unitpermutation code rep*- resentng the lettery I-fis shown. indiagrammatic formiin; lineA iiand the relativef duration of the regular pulses of. eachofl the signal` combinations is indicatedl in line. am the. starta'ndl. each oi4 the five.. selecting. pulses being Y representedl unity and4 the stop. pulse being. representedL as; 1142 times' longen. When. key IBB'. representing the letter- I' on.. thekeyboardu off the sending teletype., Writ'er is operated., key,A lever. I Il'L---L is; momen tarily. depressed against the. tensioni. of. spring', member Ill'ZA--I, to move selection, or' code;. bars ||B2 and. Illii-Btowar-dl the left;A andi selector bars;v IIi6'-|.',. Hit-42 and?. I FGI-5.. tfowardethariglt, unless; tliese, barsY are already` intl'ieir respective desiredlpositions. Theselector bars, HG1-I1. |"I`6l- 4 and M5L-5 move t'owardthe right' izo-cause their respectively associated. Contact springA members ||8;,.sucli as members. I IST-IL, [lili- 4T and! I|8`5 to. engage: space" contacts- ||9"-|",. |'|..4- and I'|B-'-5,`. respectively. The selector bars IISl--Z and lit-3 movetwvardl the left, to cause. their respectively associated'. contact spring members IIE,v such as members |'|8-2`and` IIB- 3; to engage tneir' mark contacts |2'|l`-2' and I2|l3, respectively.

The depression of key lever' |.|)|.`-|`or any'other key lever" of the keyboard; causes universal bar I'i2`to' rotate in a counterclockwise' direction around pin' |i|lan;cli'fhey freev endof'y the universal bar moves upwardly' against the tension' of coil Spring' II to causev latchm'ember" I/ILD' t'o disengage throw-out: cam I'I'i. When latch member I I Um'oveso'ut of engagement. with throwiout" cam H13, driven' clutch' member |01 is' permitted to" mesh with driving Gluten member |08" and. @am shaft Illis 'started on a revolution'througli a singie cycle. Should' there' be no'further'operation of' the' keyboard' following theoperation' of .a key', su'cl'a'skey I'lll;I latch' member l'lihaving'imme'- diately returned t'o normal' under" tne^inuence of; coil; spring' I I0", would' engage' throw-out cam I'Iattne endofitlie cycle'ofc'am shaft IUG andvk the` cam" shaft would again be' lockedinit's'normal position, selector magnet. I2| would be maintained operated in its marking position and dummy magnet' 22', would be' maintained released inits* spacing position.

In transmitting" the start-stop; five-unit' per- Imitation code signal corresponding'to theletter` I, the' space and. mark; pulses' constituting the` signal are established by'the' joint operation of the group' of' contact sets controlled by cam' shaft, Iilv and' the group of Contactlv setscontrolled` :by' code barsv MI5; during a" revolution of" the' shaft I'il';v The operation` resulting from'thetransmission`of"tl"1e signal may. be` described; in the f`o1l'ow ing'. manner:

("1) The'contact between' Contact springfmember |34 and terminal |35' is opened atth'e'beginning' of' the start fpulse, or first interval, and remains" opened for' the" duration' ofA they ve se1ect. ingwpulses oi the` signal combination. A start,

or,I space; pulse'isjsent to the operating' circuit for' terminal: |35`r being due to' the' removal of"y theA restraint;v on switch` shifter' |33 when the* stop portion |36 of shifter |33. The start, or first, interval sector of the cam, now of reduced diameter engages the peak portion |36. The dummy magnet |22 which is normally in a released condition, remains in a released condition.

(2) At the end of the start, or first interval, peak portion |32-I of switch shifter |30| continues on the cam M15-i of normal diameter for a short distance, say about 2.4-1- degrees as indicated in Fig, l-A or about per cent of the unit interval of a selecting pulse, and then engages the indentation on cam IUS-I to remove the restraint on switch shifter ISU-l. This permits the contact between contact spring member ID3-I and terminal |04-I to close during the second interval that is, for 90 per cent of the unit interval of a selecting pulse, whereby a `shortened pulse for the first selecting pulse is transmitted in a circuit extending from grounded negative battery |29, contact spring member H13-I, terminal ld-I, conductor |23-l, contact spring member IIB-l and space Contact ||9-|, conductor |21, through the winding of dummy magnet |22, to grounded positive battery |26 to operate dummy magnet; |22 in place of selector magnet |2|. Selector magnet |2| is not responsive to a space pulse and therefore remains released.

(3) Near the end of the second interval, peak portion |32| of switch shifter ISU- I leaves the indentation of cam IUE-I at a point about 2.44- degrees, in angular distance, before the beginning of the third interval and continues on cam |05| of normal diameter but peak portion I 32-2 of switch shifter ISD-2 reaches a point, say 2.44- degrees, in angular distance, beyond the beginning of the third interval where it engages the indentation of cam |05-2 to close the contact between contact spring member ID3-2 and terminal Hill-2 during the third interval, that is, for 90 per cent of the unit interval. A shortened pulse for the second selecting pulse is therefore transmitted over the circuit traceable from grounded negative battery |29, conductor |28, contact spring member IOS-2, terminal M14-2, conductor |23-2, contact spring member IIS-2, mark contact |2U-2, conductors |24, |25 and I 45, through the winding of selector magnet |2| to grounded positive battery |26. Selector magnet |2| operates in response to the shortened second selecting pulse which is marking, and dummy magnet |22 was released when peak portion |32| left the indentation of cam IUE-l as stated above.

(4) Near the end of the third interval peak portion |32-2 of switch shifter ISU-2 leaves the indentation of cam IUS-2 at a point about 2.4+ degrees, in angular distance, before the beginning of the fourth interval and continues on cam |05-2 of normal diameter but peak portion |32-3 of switch shifter IBD-3 reaches a point about 2.4-1- degrees, in angular distance, beyond the beginning of the fourth interval Where it engages the indentation on cam |05-3 to close the contact between the contact spring member |03-3 and terminal loll-3 during the fourth interval, that is, for 90 per cent of the unit interval. A shortened third selecting pulse is therefore transmitted over the circuit traceable from grounded negative battery |29, conductor |28, contact spring member ID3-3, terminal Imi-3, conductor |23--3, contact member II8-3, mar contact I 2li- 3, conductors |24, |25 and |45,

through the winding of selector magnet 2|, to grounded positive battery |26. Selector magnet (5) Near the end of the fourth interval peakl portion |32-3 of switch shifter ISU- 3 leaves the indentation of cam IUE-3 at a point about 2.44-

degrees, in angular distance, before the beginning of the fifth interval and continues on cam A IUS- 3 of normal diameter but peak portion |32-4 of switch shifter |30-4 reaches a point about 2.4-ldegrees, in angular distance, beyond the beginning of the fifth interval where i1; er1-'-v gages the indentation on cam |05-4 to close the contact between contact spring member ID3-Jl' and terminal "M -4 during the fth interval, that is, for degrees of the unit interval. A A shortened fourth selecting pulse is therefore transmitted over the circuit traceable from grounded positive battery |29, conductor |28, contact spring member ID3- 4, terminal U14-4, conductor |23-4, contact spring member IIB-ll, space contact IIS-4, conductor |21, through the winding of dummy magnet |22 to grounded positive battery |26. Dummy magnet |22 operates in response to the shortened fourth selecting pulse while selector magnet |2| which released when peak portion |32-3 left the indentation of cam IBS-3, remains released to send the fourth selecting pulse which is spacing.

(6) Near the end of the fth interval peak portion |32-4 of switch shifter I30-4 leaves the indentation of cam M15-4 at a point about 2.4-5- degrees, in angular distance, from the beginning of the sixth interval and continues on cam [l5-il of normal diameter but peak portion |3'2-5 of switch shifter ISU- 5 reaches a point about 2.44- degrees, in angular distance, beyond the beginning of the sixth interval where it engages the indentation on cam MI5- 5 to close the contact between the contact spring member |03-5 and terminal IDA- 5 during the sixth interval, that is, for 90 per cent of the unit interval. A shortened fth selecting pulse is transmitted over the circuit traceable from grounded negative battery |29, conductor 28, contact spring member H13-5, terminal IIIA- 5, conductor |23-5, contact spring member ||85, space contacts IIS-5, conductor |21, through the winding of dummy magnet I 2-2 to grounded positive battery |26- Dummy magnet |22 again operates, but now in response to the shortened fth selecting pulse, while selector magnet |2| remains in a released condition to transmit the fifth selecting impulse which is also spacing.

(7) Near the end of the sixth interval peak portion |32-5 of switch shifter ISU-5 leaves the indentation of cam IGS-5 at a point about 2.4-ldegrees, in angular distance, from the beginning of the seventh interval and continues on cam iBS- 5 of normal diameter but peak portion 36 of switch shifter |33 reaches a point where it again engages the stop segment of start-stop cam |09 to again close the contact between contact spring member |313 and terminal |35 during the seventh and last interval. A stop pulse which is always marking, is therefore transmitted over the circuit traceable from grounded negative battery |29, conductor |28, terminal |35, contact spring member |34, conductor |45, through the winding of selector magnet |2|, to grounded positive battery |25. Selector magnet |2| is operated by the stop pulse and dummy magnet I2 released when peak portion |32-5 left the indentation of cam M15-5 as stated above. Magnet |2| remains operated until the keyboard is again operated.

accepte These seven pulses `of the start-stop signal for letter '-I, as :stated above, are Vshown online liii) of Fig. 1C.

Inline c'is designatedthe 'operated positions-of the .contact spring members :H8- 1 to jM25-ii when the-codebars |'|6--'| to H-E areop'erated to ltransmit the letter I. `It is noted that in -the rst tWo 'intervals respectively corresponding to the '"stop and start pulses, vthere are no 'contacts -but for the next five lintervals which correspond to :selecting pulses Nos. 1 to 5, the-contact springmembers -I |-`8| to |18-'5 are respec tivelypos'itionedin engagement with space=con tact vv||9| mark contact 12E- 72, markcon tact 12b-J3, space kcontact ||94 'fand space contact Y||"9f5.

In lline Yd yis r`indicated the current `in and the condition lof selector magnet |-2| during the transmission-'of the -signalcornbination for letter I. Duringlthestop, or normal, interval shown Iin line'b,selectormagnet 425|' is operated. 'During'the intervals respectivelyr Vcorresponding ``to the `start pulse and the iirstselecting pulse, magnet |l2i is released. During the intervals respectively corresponding-to the Asecond and/third selecting-pulse magnet -|2| operates'forfQO per-centlof LVthe duration-of'thefintervalofeach of thesepu1ses. Dur ing the intervals of the ffourthandfifthselecting pulses, magnet |2-| '-is released -andat the-end Iof the interval corresponding to the 'iifth selecting pulsema gnetil2'| is againopera'ted and fremains operated 'until the keyboard-is again `operated.

Line `e 'indicates fthe 4letter 'I signal mpick-up which would appear Lon 4an -oscillogram vin :the

form 'of short, lsharp voltage pulses, as 'they .are

radiatedby the operation `and 'release of selector magnet 2|, -received by a Anearby radio receiving set and -recorded by an voscillograph "(both `of which are vnot shown). It will -be noted that when two or more marking lpulses occur 'in iconsecutive order as shown `for selecting pulses-2 'and 3 yin the signalvfave ofl line fb, Va short, -sharpvoltage pulse "appears Jat `each ypossible transition 'in the lcontinuous marking lpulse of 'two or more :selecting pulses 4and 4therefore a-short voltage pulse occurs in 'the plain ltext 1pick-*up at the point loic- .tween fselecting pulse No. *2 `and selecting pulse No. 3. Also, Ia voltage pulse occurs when the selector magnet 'responds to an actual lsignal transition vfrom marking -to spacing lor spacing tomarking.

Linef indicates the lcurrent A-Wave due to the contacts controlled by I'start-stop fcam 41509. In other Words, when cam shaft |06 is in itsnormal position, contactspringmember |34 and-terminal |35 are interconnected during vthe idle period of the v`teletypewriter or the time lapsing between the voperation ,of 'keys -at the keyboard. YInasmuch as the contact between Vcontact spring member '|34 and terminal |35 opens at the beginning of the :start pulse and remainsfopen for the duration of the ve follotvingselecting pulses, the next six intervals, 'representing the start and rselecting *pulses Nos. 1, 2, 3, 4 and 5,are indicated 'as open 'intervals ofcontact rspring members |34 'and '|35 and therefore no lcurrent flows through these 4contacts 'in the operating circuit of 4either selecting magnet 12| or dummy magnet |22 during [these intervals.

'Line .g 'indicates the current Wave due to the closures of the contacts associated 'with cams lS--J'to IUE-5. Sincecontact-spring mem-bers .11B-"I 'to 'I fil- 5 haveprepared circuits from'the contacts controlled by the cams, a conductive'circuit, either Ato selector magnet ='|'2| or fdummy f2 magnet |22, is closed and reopened vbyeach oi the cams, and the closures are Vfor 390 per -cen't of lthe normal interval for each 'of the selecting pulses Nos. 11, i2, 3, t4 @and i5 fas fzprov-ided ffor lby the special cuttings, or lindentations, :on `cams ||I5-I vto l'M15-5fsh'ovvn inFig. 1A.

Line h rshows the `current yfin and condition ici dummy 4magnet |22. 'Dummy magnet :|22 is .frele'asecl during lthe Y'stop yand 'the :start pulses :of a signal fcornbination but .withA respect `to the particular I combination or @letter :I the :first :selecting pulse fis spacing tofcause fmagnet :|122 tto operate. Second and third selecting v.pulses :are marking i.to cause .magnet i|22 .to release, ethe fourthgand fifth selectingpul'sesare spacing toLcause magnet |22 tofopera'te. shoulditheselecting puls'esbe of'unit duration :magnet "I 22 would remain ioperated for the Jduration :of .theifourth yand z-tth selecting pulses :but :inasmuch :as `|the :indentation on the cams :have an l'angular ydistance of :90 :Ueli 102m V0f that of a yunit length, Jor Lnormal, selecting .pulse interval, magnet "|222, having l:beenoperated `vill release at every possible itransiticniof .each signal combination.

Line-:i indicates the masking pickaup, yas iit would appear on fan gosc'illogram, iin the form of short, sharp Yvoltage :pulses radiated by the operation and release of dummy magnet 422, -received by :the :nearby radio receiving .set '(lnot shown) and recorded Eby Iv.the ioscillograph :cnot shown.

:Line fri indicates the'gcombined pick-up, that is, the .zp'ickaup indicatedinlineeqadded'to the Jickup indicated ein vfline i which would appear .on the oscillognam yin 'the form of a .uniform `pattern `of short, sharp voltage ,pulses -vas they are radiated iby the operation :and `release of .-both :selecting magnet |21 andrdummyimagnct |212. Thispat-J tern would .be ithe 4.same :for all icharaoter signals transmitted -from the keyboard.

The :deciphering Aset io'f device .|611 lutilizes repeating :relay y(.29) andfselcctor .magnet .(26) for receiving Adecipheredsignals incoming over ,line (16') ySelector magnet 1626) yupon operating, is eective'to "control .in y'a receiving printer a cam shaft of 'the itype ..shown in S. Morton :et .al. JJ. -S. Patent 1,904,164, fissued April 18, 1933 selector magnet :(26) Adesignated 2| 39 .fin -the `present application, being -fresponsive to `marking .pulses srepeated by -repeating relay {(29f) designated M3 herein land .dummy magnet .fI4-2 ibeing responsive to the :spacing pulses.

Whatis claimedis:

1. At a telegraph station, a work 'circuit path including :.a :signal ...responsive `device having ythe inherent :characteristic tof radiating :electrical impul-ses. incident :to thefsign'al :responsive piperati'on thereof, fa fdumm-y zeircuit Apath having t.electrical characteristics identical with those of said .Work circuit path n and .adapted to z'radiatie like l.electrical impulses, and .means for closing aicircuitfthrough said lwork rcircu'it :path .for marking -pulsies :and through said dummy .rcircut path :for espaoing pulses in non-.overlapping .time irelation for successiveflike nr'unlikerpulses whereby the patterns o'f :energy radiated -from said tstation .for like numbers 4ci? .tpu'lsesfin ianycombination .of marking and spacing :pulses '--arjc fiden'tica'l.

.2.'JIn Ja telegraph ftransmitter, a plurality 'of marking contacts, .fa plurality of spacing ..icontacts, a wcrkcircuit path connected `togzsaid fn'iarking fcontacts including :arisi'gn'al .responsive devine having the .inherent 'characteristic of radiating electrical :impulses incident 1to :the :signal mesponsive. operationftheredf, a 'dummy 'eircuitpath :con-

nected to said spacing contacts and having electrical characteristics identical with those of said work circuit path and adapted to radiate like electrical impulses, a plurality of contact tongues selectively positionable in engagement with said marking or spacing contacts, and a distributor for completing circuits through said contact tongues and said Work circuit path or said dummy circuit path in non-overlapping relation whereby the pattern of energy radiated from said transmitter includes like components of energy from both paths and is uniform for all signal cornbinations.

3. In an impulse transmission system, means for causing to be generated different groups of different kinds of unit length signaling pulses, a plurality of transmission channels, selectably operable contacts, successively operable contacts, means under the joint control of said selectably operable contacts and said successively operable contacts for selecting in response to the operation of said first-mentioned means one or the other of said channels, as desired, a signaling pulse responsive device in each of said channels having the inherent characteristic of radiating electrical impulses incident to the signal responsive operation thereof, one of said devices being operated and released in response to each of a certain kind of said signaling pulses transmitted from said selecting means and the other being operated and released in response to each oi the other kind of said signaling pulses, said devices, when opern ated and released, radiating energy components that are alike and therefore indistinguishable to detect which of the energy components were radiated by either one of said devices.

4. In a telegraph system, means for selecting diierent groups of unit length signaling pulses of diierent types to be transmitted, a transmission channel including an operable device arranged to operate and release in response to each of the pulses of one type and having the inherent characteristic of radiating electrical impulses incident to the signal responsive operation and release thereof, another transmission channel including an operable device arranged to operate and release in response to each of the pulses of another type and having a like inherent characteristic, selectably operable contacts for conditioning both of said operable devices for operation, and successively operable contacts cooperating with said selectably operable contacts in response to the operation of said selecting means for operating and releasing one of said devices in response to each of the pulses of one type and the other of said devices in response to each of the pulses of another type, whereby said devices radiate an energy component at each possible change from one type of pulse to another, said components of all groups of signaling pulses being alike and therefore the components of one group being indistinguishable from those of any other group.

5. At a telegraph station, a circuit comprising a work path having the inherent characteristic of radiating electrical impulses incident to the operation thereof, and a dummy path having electrical characteristics identical with those of said work path and adapted to radiate identical electrical impulses, a telegraph instrumentality for transmitting permutation code signals, and having operable bars arranged to be automatically positioned in accordance with the impulses of different types in each of said signals, a pair of terminals and a movable contact member therebetween controlled by each of said bars and arranged to condition either of said paths depending on the type of the corresponding impulse of each of said signals, cams lixedly mounted on a start-stop rotatable shaft arranged to rotate through one revolution in response to each of said signals and contacts respectively controlled by said cams and arranged to close and then open in successive order whereby, in response to each impulse of each of said signals, one or the other of said paths depending upon which is conditioned for operation at the time, is closed, the closings of said paths producing patterns of energy radiated from said station for like num bers of impulses in any signal combination, which patterns are identical for all said signals.

6. At a telegraph station, a circuit comprising a work path having the inherent characteristic of radiating electrical impulses incident to the operation thereof and a dummy path and adapted to radiate identical electrical impulses, and a teletypewriter for transmitting permutation code signals of marking and spacing impulses, said teletypewriter having means for effectively closing and effectively reopening said circuit through said work path during each marking impulse and through said dummy path during each spacing impulse of the permutation code telegraph signals, whereby each of the patterns of energy radiated from said station includes like components of energy from both said paths and said patterns are uniform for all signal combinations.

WALTER M. BACON.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 1,244,477 Delany c Oct. 30, 1917 2,401,454 Bemis June 4, 1946 2,405,569 Fitch et a1 Aug. 13, 1946 2,417,847 Thompson Mar. 25, 1947

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