Патент USA US2405991код для вставки
Patented Aug. 20, 1946 2,4 5,9% UNITED STATES PATENT GFFIC 2,405,991 SECRECY SYSTEM Harold H. Beverage, Riverhead, N. Y., and Rich ard E. Mathes, Westfield, N. J., assignors to Radio Corporation of America, a corporation of Delaware Application July 31, 1940, Serial No. 348,756 12 Claims. (Cl. 178--22) l 2 This invention relates to signalling systems and especially to telegraph systems. Its object is to insure secrecy in the transmission of messages and, further, to provide a system in which mes sages may be transmitted and received in char acters of a well known code, but only the signal ling impulses are so altered before transmission equal length are transmitted. The machines for transmitting the signals are labeled I, 2, 3 and are well known automatic transmitters which re telegraph transmitting devices, respectively. spond to signal characters impressed on the per forated tape 4. The perforations of the tape may be effected by any suitable perforator (not shown) such as the Kleinschmidt apparatus, well known in the art. This tape is utilized to control the transmitters I, 2, and 3 which may be of the Wheatstone automatic tape transmitter type for actuating a circuit in accordance with the perforations in the tape. The individual trans mitters are each driven by a shaft ‘í which is connected to a motor 6. The motors S, 6 of the transmitters I, 2 and 3 rotate at the same speed and are synchronized as to speed and phase by pulses received over lead 50 from a commutator In brief, the present invention employs at each channel or transmitting position an interrupting 5l mounted on motor 39 in a manner shown and described in more detail in Figure l of United over the transmitting medium that they are un intelligible to unauthorized persons intercepting them, The invention is particularly applicable to a multiplex communication system designed to transmit a combination of signals having equal length code characters and signals having un equal length code characters, such as may em anate from printer apparatus and Morse code device such as a cam or switch for reversing the 20 States Patent 2,010,505, supra. Of course, any other suitable synchronization circuit may be em sense of the signals at arbitrarily selected inter vals; and at the central station at which the mul tipleX distributor is located for assigning the in ployed. The power supply apparatus which serves to supply positive and negative potentials to the dividual message channels to a common transmis contacts 9.and I 0 of each transmitter is ar sion medium, it is proposed to interlace or scram 25 ranged in circuit with a suitable double pole ble the individual message channels as they are switch II, which in turn responds to movement assigned to the distributor at arbitrarily selected of a cam follower I2 resting on the periphery of intervals. At the receiver there is provided simi a cam I3, in turn linked through a shaft I4 and lar mechanisms for unscrambling the channels gears to the shaft l. The output energy from and similar cams and switches for restoring the each tape transmitter I, 2, 3 is derived from an sense of the signal characters so that they can ` armature I5 adapted to contact either 9 or I0, be recorded correctly. For a detailed description depending upon the perforations in the tape, and of the type of multiplex system to which the pres ent invention is particularly applicable, reference is made to United States Patent No. 2,010,505, c.: Cn granted August 6, 1935, to Callahan et al. Apparatus for accomplishing the results of the present invention is shown in the accompany ing drawings, wherein: Figure l illustrates schematically a complete transmitting system in accordance with the pres passes over connection I6 to a wiper arm of a multi-bank rotary selector switch before being passed on to the multiplex distributor. Although tape transmitters have been shown for the indi vidual channels, it should be understood that if desired any tape transmitter can be replaced by suitable printer apparatus of the well known tele type start-stop type, in which case there will be ' associated with each printer and located between ent invention; the printer and the rotary switch suitable signal Figure 2 illustrates the manner in which inter lacing is effected at the banks of the rotary storing mechanism in the manner described in Callahan Patent 2,010,505, supra. The lines I6, I6 extending to the tape trans mitters connect to the wiper arms Il of the three bank rotary selector switch, the individual banks switch; Figure 3 illustrates a receiving system in ac cordance with the present invention; and Figure 4 illustrates a feature which can be used. of which are labeled I8, i9 and 20 and shown in the receiving system of Figure 3 to overcome separated in order to clarify the connections in 50 the drawings. In. practice, all three banks 5S, I9 possible contact transition difficulties in the re ceiving system. Referring to Figure 1 in more detail, there are ’ and 20 are closelj,î adjacent to one another and have their _wiper arms I'I, l'! simultaneously con shown three individual message channels (la trolled and movable over correspondingly located beled channel #1, channel #2, and channel #3) over which regular Morse signal characters of un- f dash line 22 extending from the stepping magnet contacts by means of a stepping magnet 2 I. The 2,405,991 4 3 comprises a plurality of segments 26, 21 and 28, each segment being associated with a single chan 2| to the wiper arms I?, I1 is intended to indicate the unicontrol action of all three wiper arms. This type of rotary selector switch is well known in the art and is of a type commonly used in nel at a time, and a brush assemblage 33 adapted to sweep over the segments and to obtain there from the signal units or pulses transmitted by the channel equipment comprising transmitters I, 2 and 3. The brush assemblage 33 (which is telephone and telegraph practice. Connected to the first contacts o_f the bank of the rotary switch are lines 23, 24 and 25, re-` spectively, which extend to distributor segments 26, 21 and 2B of the multiplex distributor, each segment being individual to a channel. The con connected to the multiplex equipment 32) is ar ranged to make one revolution for each dot length 10 of the automatic transmitter equipment, this dot -length comprising the basic unit (the baud) which is equal in length to the individual unit pulsetransmitted over each channel I3. In the is connected at an arbitrary interVaL'depending present instance, since a three channel circuit is upon the position of the wiper, in turn controlled by the stepping magnet 2l to a diiïerent segment 15 shown, the distributor is arranged to supply to the multiplex transmitting keyer 32 at most one ' of the multiplex distributor. Only three contacts tacts on the rotary switch are interlaced or scrambled in such manner that each channel i6 of each bank of the rotary selector switch are shown suitably connected and interlaced in Fig ure 1, in order to illustrate the method of inter lacing, although al1 ten contacts of each rotary 20 switch are shown interlaced in more detail in third of a baud from Veach signal unit, this one third being the length of each unit of signal taken from each of the respective channels successively, thus throwing away the other two-thirds of the dot unit of each signal in each channel which is Figure 2. More specifically, it will be noted by referring to Figure 2 that the first contact of the ñrst bank I8 (to which lead 23 is connected) is connected to the second contact of the third 25 bank, and then to the third contact of the third bank, and to the fourth contact of the second bank, etc. The ñrst contact of the second bankV later restored by rebuilding the signal in the ‘ rotary selector switch, that when thewiper arms part of each one-third portion, and to discard receiver. The multiplex transmitting keyer equipment 32 which in turn actuates the radio transmitting equipment 34 is assigned to each of the channels #1, #2 and #3 and their respective lines i6, I5 in succession, for a time equal to one of these one-third dot or baud portions. It will be apparent from Figure 1 that al i9 (to which lead 24 is connected) is shown con nected to the second contact of the `i'lrst bank 30 though three channels are shown, any number of channels may be used. For three channel and to the third contact of the second bank and working, normally only one-third of each signal to the fourth contact of the third bank, etc. The component is actually operative for each chan ñrst contact of the third bank 20 (to which lead nel, and similarly for other numbers of channels. 25 is connected) is co-nnected to the second con tact of the second bank and the third contact of 35 Although for the sake of simplicity it has been mentioned that one-third of a dot length of each the ñrst bank, and to the fourth contact of the unit is assigned to .the transmitter keyer 32, ñrst bank, etc. It will thus be seen that as the actually it is preferred to use only a very small wiper arms I1, l1 move over the contacts of the are on the first contacts, the ñrst channel will 40 the remainder of the dot length of each channel be connected through line I6 to lead 23, the sec unit. This mode of operation has been found ond channel will be connected through its par to increase the tolerance of Variation permitted ticular line It to the lead-2 4, while the third chan a signal due to fluctuations andV bias distortion, nel will be connected through its line I6 to lead noise,v etc. The multiplex transmitting equip 25. However, when the wiper arms I1, l1 are 45 ment 32 functions to produce a composite sig on the second contacts of the switch, the iirst nal composed of successive one-third dot length channel will now be connected to lead 24, while portions from the three channels consecutively. the second channel will be connected to lead 25, This equipment with which the distributing and the third channel will be connected to lead brush assemblage 33 is connected comprises es ` 23. In this way there is obtained a scrambling 50 sentially a locking circuit and a shunt keyer ar or interlacing of channels with the leads 23, 24 rangement for producing tone signals in trans and 25 extending to the segments of the multiplex mission line 35 which tone signals c-orrespond to distributor, thus assuring additional secrecy, that the composite signal received from the multiplex is, more than that provided by the feature of the distributor, these tone signals in turn, controlling cams I3, i3. The stepping magnet 2|, of course, 55 the radio frequencyemanations in line 35 ex determines when the wiper arms should advance tending to the antenna `3l. The locking circuit to the next contact, and the operation of this in 32 comprises essentially two electron discharge stepping magnet can be arbitrarily selected >to devices (not shown), which have their anodes provide random interlacing, and this is done by and their control electrodes resistively intercon 60 connecting the stepping magnet to a cam fol nected in a manner such that the performance lower 29 whose closure with a contact 30 leading has two >degrees of electrical stability. These to a source of positive potential is determined devices are unstable when both are drawing cur by a cam 3l. This cam has'any desired number rent but stable when one tube is passing current of arbitrarily selected cam segments to cause the closure of contacts 29 and 30 at certain inter 65 and the other blocked or prevented from passing current. The change from one condition of sta vals. By ïmeans of the cam 3l and its driving ble equilibrium, such as when one tube is blocked mechanism, the stepping magnet 2| `may be and the other passing current to the other con caused to operate the selector switch at every dition When the last tube is passing current and baud or at any desired integral number of bauds , 70 the ñrst tube blocked, or the reverse, is caused by or combinations thereof. the presence of predetermined potential on the The multiplex distributor consists 0f any suit brush _assemblage 33. For a more amplified de able means for assigning the various channels, scription of such manner of telegraph communi through leads 23, 24 and 25, to the multiplex cation reference is made to United ‘States Patent transmitting keyerV equipment 32. In the ar rangement shown in the drawings, the distributor _'15 2,010,505, supra, and also to United States Patent 2,405,991' 5 6 1,844,950, granted February 16, 1932, to J. L. are identical in construction, although, if desired, the cams for the diiîerent channels may be con structed differently to have a diiîerent number of segments. The received message signals which are changed in character by the cams I 3, I3 at Finch. Y The multiplex distributor is driven by means of a shaft 38 which is geared to drive motor 39, the latter in turn .being also geared to the cam 3|. This gearing controls the speed of rotation the receiver (that is, restored in sense to their original form) are passed on to suitable locking Referring now to the receiver of Figure 3, the circuits 48. These locking circuits consist essen tially of a pair of electron discharge devices which composite signals are received over any suitable type of antenna system 40, amplified and de 10 have their anodes and control electrodes resis tively interconnected to provide two degrees of tected in well known manner in equipment 4I, electrical stability in the same manner as the and~ then transmitted over transmission line 42 locking circuits in apparatus 32 oi the transmit to a suitable central ofñce where the receiving of the multiplex distributor and the cam 3l . multiplex distributor -43 assigns the received in coming signals to their respective channels, in ter, the locking circuits at the transmitter and receiver being substantially of the same construc tion. Reference is here made to United States which the received signals are rebuiltA to their original form as in the transmitting station, the PatentsV 2,010,505 and"1,844,950, supra; for fur portions suppressed at the transmitting station ther details of a well known form of locking cir cuit which may be employed. A suitable utiliza being restored in the receiving system. Distributor arrangement y43 is driven by a drive 20 tion device, such as an ink recorder or other in motor 44 which is held in synchronism with the strument, may be connected to each locking cir multiplex distributor driving mechanism 39 at cuit 48 of the receiver. In order .to avoid the production of undesirable the transmitting station by means of a suitable extraneous short clicks in the locking circuit 4S correction unit (not shown) which may be con of Figure 3, due to the fact that the closure of trolled by the incoming signals. This correction unit for synchronizing the motor ¿M with the mo the contacts of relay 65 and those of cam I3 tor 39 of the transmitter may be of a type de might not be exactly simultaneous, it is proposed scribed in United States Patent 2,010,505, supra, to employ »a circuit as shown in Figure 4 which includes a kicker commutator 52 to be inserted between each locking circuit 48 and its associated cam i3 in each channel. The knicker commu tator 52 includes a pair of brushes 53 designed to or of a type shown in Mathes United States Pat ent No. 2,062,009, granted November 24, 1936. Associated with the individual segments of the multiplex distributor d3 are the banks IS', I9’ and 20’ of a rotary selector switch of a type iden tical with that described in connection with the transmitter. The contacts of this rotary selec tor switch at the receiver are interlaced in the same way as the contacts of the rotary switch be connected together at predetermined intervals by a short-circuiting copper bar 54 mounted on the insulated surface of 4a rotating drum-like ele ment driven by `a shaft 55. The rotation of the drive shaft 55 is of course synchronized as to at the transmitter, and the stepping magnet 2i’ speed with the other driving units to produce clo for the rotary switch at the receiver is arranged to operate by means of cam 3i’ in synchronism sure of the controls 53 only at the central por tion of each band of received signal. Thus the kicker 52 selects the central portion of each band as it is passed to the locking circuit 48 and uses the kicks produced thereby for the operation of the locking circuit 43. In this way the kicker commutator permits a certain degree of transi tion time at the contacts of relay ¿l5 and cam I3 with the operation of the cam 3i at the trans mitter. Cam 3i' at the receiver is, of course, of identical construction as the cam di at the trans mitter, and both of these cams rotate in syn chronism, whereby the rotary selector switch at the receiver unscrambles the signals caused by the scrambling arrangement of the rotary switch at the transmitter, thus producing on leads 23', 24’ and 25’ signals substantially identical in form to the signals on leads i5, i5 and It respectively, at the transmitter. Associated with each ci the leads 23', 2li’ and 25' there is provided a suitable relay 45 of the vacuum or electromagnetic type which is operm ated by the rectined signal assigned to its asso without affecting the signal produced by the lock ing circuit. For a more detailed description of this form of ' kicker commutator reference is made to Mathes Patent 2,038,375, April 2l, 1936 (Figure 2 thereof). In the operation of the transmitter of Figure l, the rotation of cam I3 in each channel will move the cam follower i2 up and down in accordance ' with depressions on >the cam. Movement of the In cam follower I2 will accordingly cause movement the output of relay ¿i5 there is provided a double pole switch II' which is moved in response to the, receiver are of identical construction as the cams of the double pole switch II, thus changing the polarities applied to contacts 9 and I0 by the power supply. The circuit path from the power supply through the switch il to the contacts S and i0 of the automatic transmitter of each I3, I3 at the transmitter, and are driven simulta neously at the same speeds as the cams at the channel will be obvious from a mere inspection of the drawings. The change in sense of the ciated lead extending te the rotary switch. movement of a cam follower i.. periphery of cam i3. resting on a The cams i3, i3 at the polarities applied to contacts 9 and I0 by the transmitter. For this purpose there is provided at the receiver a drive motor At which drives the cams 65 cam I3 is arranged to occur in synchronism with the mechanism in its associated transmitter I, 2 through a suitable shaft and gearing arrange or 3, whenever it tends to move armature I5. ment indicated by the dotted line 4l. The Ino Putting it another way, the polarity reversals tor 46 is, of course, synchronized to operate at produced by the cam I3 in each transmitter mair exactly the same speed as the motor Ei, which is at the transmitter and is controlled as to speed 70 occur where a dot or baud of unit length is to be transmitted only at the end of the baud; and phase from commutator 52 mounted on mo where a dash having a length equal to a plural ity of bauds is to be transmitted, the polarity re connection with motor E in the transmitter. At versal may occur at the end of any of the com this time it should be noted that the transmitting and receiving cams i3, I3 for the same channel 75 ponent bauds constituting the dash, The oc tor #3Q in the same manner as is described in 2,405,991 7 currence of lthese reversals is determined bythe arrangement of the cam and Ymay occur at the end of every baud or at multiple sequences there of. For example, the cam may be constructed to produce reversals at the end of every four bauds, or to produce reversals at non-uniform periods to further insure secrecy. Further, the cams may be replaced by tape transmitters serving thev same purpose. Any suitable type of synchroniz ing system may be employed for insuring proper phasing and synchronization of the various ele ments of the entire system. What is claimed is: so long as these periods include an integral num l. In a multiplex telegraph system, the meth ber of bauds, although the cams for different od of signal communication which comprises transmitters may have different constructions to produce reversals at the end of a different num 10 transmitting over individual lines a plurality of message signals corresponding to the number of ber of bauds. channels in the system and whose elements‘are of unit length and multiples o-f unit length, changing a characteristic of certain elements of and 25 depending upon the interlacing at .the 15 said signals at predetermined intervals, and as signing said lines in a predetermined irregular banks I8, I9 and 20 of the rotary selector switch. 'I'he stepping magnet 2l under control of the cam sequence to a transmission medium. 2. In a-multiplex telegraph system, the method 3| will determine the intervals at which the interlacing occurs. The multiplex equipment of signal communication which comprises trans per se illustrated by .the multiplex distributor 20 mitting over individual lines a plurality of mes assigns only a very small portion of the sign-a1 on sage signals corresponding to the number of each channel to the keyer and locking circuit 32 channels in the system and whose elements are of unit length and multiples of unit length, as for transmission over the antenna 31. The signals sent out by the transmitters of the three channels over lines I6, I6 are assigned at random to different ones of the leads 23, 24 Thus, it will be seen that there are four c0 signing said lines in irregular order to a trans operative features which contribute to assure 25 mission medium, dividing the successive basic secrecy in the transmission of the signals. The time units of the message characters of each iirst feature comprises cam I3, which produces channel into substantially equal portions of like reversals in sense of the signals at arbitrarily se number not less than the total number of chan lected intervals. The second feature is the rotary nels used, and transmitting over said medium a selector switch which by its interlacing causes 30 composite signal formed by combining equal por the signals to go to the multiplex distributor over tions from thesuccessive channels consecutively. different leads at different times. The third fea 3. In a multiplex telegraph system, the method . ture resides in the cam 3| at the transmitter of signal communication which comprises trans which controls the random or arbitarry stepping mitting over individual lines a plurality of mes or operation of the magnet 2I which causes the sage signals corresponding to the number of wiper arms I'I to change position at arbitrary channels in the system and whose elements are intervals determined by cam 3l and its speed of of unit length and multiples of unit length, rotation. The fourth feature lies in the multi changing the sense of some of the signals prior plex equipment per se which selects only a small to transmission over said lines and at predeter portion of each signal unit and discards the re 40 mined discrete intervals, assigning said lines in maining portion of the signal. irregular order and at arbitrarily selected inter At the receiver there are employed means vals to a transmission medium, dividing the suc which correspond to the foregoing means at the cessive basic time units of the message characters transmitter for unscrambling and restoring the into equal portions of like number as the total signals to their original form. For example, the L. number of channels used, and transmitting over cams I3 at the receiver function to restore the said medium a composite signal formed by com signals back to their true sense or true polarity, bining equal portions from the successive chan which they had before they were affected at the nels consecutively. transmitter by the polarity reversal cams.-V The 4. In a multiplex telegraph system, the method three bank rotary selector switch at the receiver of signal communication which comprises trans is interlaced in identical manner as the rotary mitting over individual lines a plurality of mes selector switch at the transmitter for unscram sage signals corresponding to the number of chan bling signals produced by the interlacing at the nels in the system and whose elements are of unit transmitter; and the cam 3l’ at the receiver of length and multiples of unit length, changing the like construction as cam 3i at the transmitter ' » sense of some of the signals prior to transmission and operating at the same speed, causes the wiper over said lines and at predetermined discrete in arms of the receiving rotary switch to move in tervals, and assigning said lines in irregular order synchronism with the movement of the wiper at arbitrarily selected intervals to a transmission arms on the rotary switch at the transmitter. medium. Finally, the locking circuits 48 at the receiver 60 5. In a multiplex telegraph system, the method associated with the channels function to restore of signal communication which comprises trans or rebuild the individual signal units to their mitting over individual lines a plurality of mes original full length, whereby the portions of the sage signals corresponding to the number oi' signal units discarded at the transmitter are channels in the system and whosel elements are filled in at the receiver. of unit length and multiples of unit length, It should be understood that the present in changing the sense of some of the signals prior vention is not limited to the precise arrangements to transmission over said lines and at predeter of parts illustrated in the drawings, since various mined discrete intervals, which terminate only modifications may be made without departing at the end of a unit length, and assigning said from the spirit and scope of the invention. The 70 lines in irregular order at arbitrarily selected in rotary switches may be of any suitable form and tervals to a transmission medium. ' may comprise any desired number of contacts. 6. In a multiplex telegraph system, a transmit- , The cams may be of any suitable construction ter employing for each channel a code having and are not limited in form to those illustrated characters composed of one or more signal units in the drawings and may be changed frequently of fundamental time duration, leads extending Y n 2,405,991 10 from a transmitting multiplex distributor to said transmitters, switching means associated with constituting a component element of a character, rotating mechanisms for said transmitters, means said leads and located between said transmitters and said distributor for assigning said transmit >ters at different .predetermined irregularly spaced for synchronizing the speed of said mechanisms, times to diiîerent ones of said leads, a transmis leads extending from a transmitting multiplex distributor to said transmitters, switching means associated with said leads and located between sion medium, said distributor serving to assign said transmitters and said distributor for assign said medium to said leads in succession and to each for a period of time equal at most to the ing said transmitters at different times to differ ent ones of said leads, a transmission medium, longest period of which the duration of the funda 10 said distributor serving to assign said medium to mental time unit is an exact multiple of the num said lines in succession and to each for a period ber of channels. of time equal at most to the longest period of 7. ~A multiplex -telegraph system in accordance which the duration of the fundamental time unit with claim 6, characterized in this that said means is an exact multiple of the number of channels. l1. In a multiplex telegraph system, a trans for assigning said transmitters at different times 15 to different ones of said leads comprises a multi mitter for each channel employing a code hav ing characters composed of one or more signal bank rotary selector switch, the contacts of said banks being interlaced to provide connections units of fundamental time duration, means at each transmitter for reversing at predetermined between said leads and said transmitters which change in accordance with a predetermined 20 intervals the sense of the signals to be transmit schedule as said switch advances. ted, said reversals in sense being arranged to occur 8. In a multiplex telegraph system, a transmit only at -the end of a unit length of signal con Iter employing for each channel a code having stituting a component element of a character, characters composed of one or more signal units rotating mechanisms for said transmitters, means of fundamental time duration, leads extending 25 for synchronizing the speed of said mechanisms,from a transmitting multiplex distributor to said leads extending from a transmitting multiplex transmitters, switching means associated with distributor to said transmitters, switching means said leads and located between said transmitters associated with said leads and located between and said distributor for assigning said transmit said transmitters and said distributor for assign ters at different times to diiïerent ones of said ing said transmitters at different times to diiîer leads, a transmission medium, said distributor ent ones of said leads, a transmission medium, serving to assign said medium ,to said lines in said distributor serving to assign said medium to succession and to each for a period or” time equal at most to the longest period of which the dura tion of the fundamental time unit is an exact multiple of the number of channels, a receiver for receiving the signals sent out over said trans mission medium, a plurality of receiving circuits associated with the different channels of said system, a receiving multiplex distributor for suc cessively assigning the output of said receiver to different ones of said receiving circuits for a period of time to each receiving circuit equal to a fraction of the period during which each trans mittei- is assigned to the transmission medium, switching means located between said last dis tributor and said receiving circuits for changing the connections of said receiving circuits to said distributor at such times and in predetermined manner to conform with the changing assign ment of the transmitters to their associated leads, whereby the receiving circuit of each channel is associated only with the transmitter for the same channel. 9. A multiplex telegraph system in accordance with claim 8, characterized in this that the switching means associated with both the trans mitting and receiving multiplex distributors are said lines in succession and to each for a period of time equal at most to the longest period of 35 which the duration of the fundamental time unit is an exact multiple of the number of channels, a receiver for receiving the signals sent out over said transmission medium, a plurality of receiv ing circuits associated with the diiîerent chan 40 nels of said system, a receiving multiplex dis tributor for successively assigning the output of said receiver to different ones of said receiving circuits for a period of time to each receiving circuit equal to a fraction of the period during 45 which each transmitter is assigned to the trans mission medium, switching means located be tween said last distributor and said receiving cir cuits for changing the connections of said receiv ing circuits to said distributor at such times and 50 in predetermined manner to conform with the changing assignment of the transmitters to their associated leads, whereby the receiving circuit of each channel is associated only with the trans mitter for the same channel, and means at each 55 receiver operative in synchronism with the sense reversal means at the transmitter for the same channel for restoring the sense of the signals. l2. In a multiplex telegraph system wherein signals are composed of marking and spacing ele similarly arranged multi-bank rotary selector switches, the banks of each switch having its con 60 ments of unit length and multiples of unit length, the method of rendering communication secret tacts interlaced in predetermined manner, said selector switches operating in synchronism, there being motor operated means provided for driving the distributors synchronously. which comprises periodically reversing the polar ity of the impulses corresponding to said mark ing and spacing elements, assigning signal im 10. In a multiplex telegraph system, a trans pulses of one message at irregular intervals to different ones of a plurality of multiplex channels in the system, and assigning signal impulses of other messages at the same irregular intervals to the remaining ones of said channels. mitter for each channel employing a code hav ing characters Composed of one or more signal units of fundamental time duration, means at each transmitter for reversing at `predetermined intervals the sense of the signals to be transmit 70 ted, said reversals in sense being arranged to oc cur only at the end of a unit length of signal HAROLD H. BEVERAGE. RICHARD E. MATHES.