US2312897A - Method of transmitting signals - Google Patents

Description

March s. GUANELLA EI'AL 2,312,897

METHOD OF TRANSMITTING SIGNALS Filed Oct. 9, 1940 5 Sheets-Sheet l Mar 2, 1 G. GUANELLA EI'AL.

METHOD OF TRANSMITTING S IGNALS 5 Sheets-Sheet 2 Filed Oct. 9, 1940 /5 f Z-A? ch 2,1943. cs. GUANELLA EI'AL 2,312,397

METHOD OF TRANSMITTING SIGNALS Filed Oct. 9, 1940 5 SheetsSheet 3 G. ,GUANELLA ETAL METHOD OF TRANSMITTING S IGNAL5 5 Sheets-Sheet 4 Filed Oct. 9, 1940 March 2, 1943.

G. GUANELLA ET AL METHOD OF TRANSMITTING SIGNALS 5 Sheets-Sheet 5 Patented Mar. 2, 1943 METHOD OF TRANSMITTING SIGNALS Gustav Guanella and Walter Ernst, Zurich,

Werner Lindecker, Ennetbaden, and Marcel Gabriel, Baden,

Switzerland, assignors, by

mesne assignments, to "Patelhold Patentverwertungs-& Elektro-Holding A.-G., Glarus, Switzerland, a joint-stock company Application October 9, 1940, Serial No. 360,516 In Switzerland July 14, 1939 20 Claims. (01'. 179-15) According to the known systems and arrangements for the transmission of signals, these are distorted at the transmitter end so as tov render them unintelligible to unauthorised receivers. The received signals can then be freed from'this distortion by means of correspondingly adjusted devices so that they can be understood by the v authorised receiver.

This distortion can be made particularly effective if the sequence of certain parts of the signal is altered in accordance with a definite program. This scrambling of the time sequence of the signals can be achieved in a known manner by means of a switching-over device which transmits the signals in a constantly recurring sequence over various parts of a time-delay device, these parts being characterised by unequal retardation times. The individual signalling elements a, b, c, d the duration of which To corresponds to the constant distance between two contacts of the switching device, are therefore retarded by the at least partly difierent times ta,

ts, to ,so that with a suitable choice of retardation times the new signal b, d, a, c, can for instance be formed.

The program for this scrambling repeats itself after each revolution of the switching-over device; that is to say each group of n elements the duration of which T1 corresponds to a complete revolution of the switching-over device, is scrambled in the same manner. By means of a similar apparatus operating in synchronism, the elements of the received signal are again retarded so that the total retardation time Tz-is the same for each element. In this manner the original sequence of elements is restored and the signals are received free from distortion but with a total retardation Tz.

For constructional reasons the number of switch segments which the change-over switch can accommodate is limited, and therefore the number of elements 11. per group is also restricted. It is thus possible that an unauthorised receiver by means of systematic trials may discover the scrambling key in a comparatively short time by rearranging the received signals according to the deciphered part of the signal consisting of 'n elements. Since the scrambling program repeats itself after each group of n elements the complete message can thus be deciphered.

This disadvantage ofthe known systems and arrangements is avoided according to the invention whereby before transmitting the intermediate signals resulting from a first scrambling of the elements in accordance with a first partial program which repeats itself after time intervals T1, these intermediate signals are scrambled a second time according to at least one further partial program which repeats itself after difierent intervals of time. transmitted message must first be deciphered to obtain the last intermediate signal formed at the transmitter end and from this by means of at least one further deciphering the original message is finally obtained. This new method of scrambling and the apparatus required are ex plained by means of the constructional examples illustrated in Figs. 1-5 of the accompanying drawings in a diagrammatic manner.

Since with the method of multiple scrambling already briefly described and formingthe subject of the present invention, the various partial scrambling programs repeat themselves after unequal periods of time, this multiple scrambling is effected according to a complete program which repeats itself after a time which is greater than the sum of the recurring periods of all the partial programs. If each scrambling is efiected with elements of equal length the various partial programs must obviously be based on groups having an unequal number of elements. It is advisable to select numbers for the elements which are not mutually dividable. A first partial program having groups containing m elements and a second partial program with groups of n elements all equally long, when used one after the other for multiple scrambling, result in a complete program which repeats itself only after mxn elements because it is only after the lapse of m n elements that the beginning of each partial program coincides again.

An alteration in the first partial program cannot be compensated by altering the second partial program in order to maintain the same complete program, because both partial programs always recur at different times. For the same reason a mistake in the program of the first partial diciphering cannot be continuously corrected by altering the second partial deciphering; that is to say faultless complete deciphering is only possible when the intermediate signals obtained after partial deciphering exactly correspond to the intermediate signals at the transmitter end. Since the intermediate signals are,

however, still in cipher, that is to say represent an unintelligible message, the correct intermediate signals at the receiving end corresponding to the intermediate signals at the transmitter end are not such that they can be understood. It is therefore impossible to determine the "correct" At the receiving end the intermediate signals and subsequently the original message from the received signals merely by systematic trials. Unauthorized deciphering of received signals by means of systematic trials is therefore rendered extremely diflicult.

Under certain circumstances it may, however, be possible by systematically altering the various receiving keys to obtain an intelligible series of elements from the received signals, whereby the number of such elements does not exceed the number of elements per group. This temporary deciphering of a' short series of elements can occur as a result of an exceptional coincidence of entirely incorrect partial deciphering programs which produce incorrect intermediate signals. Such a coincidence repeat itself after passing through the complete scrambling program. In the example given above where there is a double scrambling in groups of m and n elements, temporary deciphering of a short series of elements would recur only in comparativel large intervals of m n elements. Conditions for unauthorised decipherlng are considerably more unfavourable if a large number of single scramblings are used. For instance, four successive individual scramblings in groups containing 9, 10, 11 and 13 elements result in a total scrambling according .to a program which repeats itself only after 9X10X11 13=12,870 elements. .A'

temporary correct deciphering. of sabout 10 ele-. ments attainedby trials, which repeats itself at intervals of more than 10,000,. cannot serve .to

render the sense or contents of the completemesj sage in any way intelligible. A special advan tage of thenew method is that the successive individual scramblings can be performed in groups having a small ,numbero'i' elements and short is considerably smaller than that required for the simple scrambling systems used hithertmdespite the fact that a much higher degree of secrecy is achieved.

The drawings illustrate the invention, showing several modifications and applications thereof. In the drawings:.

Fig. 1 shows a transmitting device and receiving device according to the invention;

Figs. 2 to 5 show circuits for sending and receiving multiscrambled signals; s

Fig. 6 shows the fundamental system of connections for a scrambling device;

Fig. 7 shows a special construction of scrambling key;

. Fig. 8 shows a scrambling device provided with a steel tape time-delay device;

Figs. 9 to 11 show circuits for sending andvreceiving scrambled signals with the device of Figs. 6 to 8;

Fig. 12 shows a scrambling device having a single signal carrier and two switch elements;

Fig. 13 shows in detail a device similar to that shown in Fig. 12;

Fig. 14 shows a modified form of the apparatus of Fig. 13; and

Fig. 15 shows a circuit for two scrambling devices, as shown in Fig. 12, and an amplifier.

In the constructional example illustrated in Fig. 1 of the drawings S1, S2, S3 represent three ciphering devices at. the transmitting end and E1, E2, E3 the corresponding deciphering devices at the receiving end. These devices are equipped with retarding mean the delay times of which are altered by the change-over devices U1, U2, U3, V1, V2, V3 in a periodically recurring succession is obtained again. i

that is to say,-the first element is brought into the second place of the same group and the third element into vthe'first place of the next group. so that from the original signal Zo=abcdejghiklmn0pthe first intermediate signal Zi=-acdbfyeikhmnlp-ois formed. The second ciphering device 5: with the tour-contact switch U: operates for instance in accordance with the key number ment into the first place of the next group and so on, so that the second intermediate signal Zz=-'-- a dcfbegkimhln-p -o is formed. Inv accordance with the keynumber I .ll" P =41532 a further and"final scrambling in'groups of five elements is accomplished byvmeans'of the switch device S3 in order to'produce the signal I 3=' F fii. a T d if c e b'QTi IC-jhn l-n p p 9 to be alarmed. This s gnal is forinstance transmitted through the channel L. At the receivingend the first deciphering device E1 with the five-step switch V1 scrambles, the transmitted signal Z3 according to a key number Q.=2541-3 i which is associated with the partial program, Pa on the transmitting'side, and thus producesthe second intermediate signal t 2z= r a d c f bjei-g k i m hi a-epic Then according toja further key number a which i assoclated with the ke instigate the transmitting side and happens with it, the first intermediates'ignal.

Z1=-'a-cdbfgeikhmnlp 'o-c is produced by the device E2 from the intermediate signal Z2. Finally with the device E: and the key number to coincide Zo=-abcdefghi]clmnap With this arrangement the transmitting and receiving end associated with each other,namely U1 and Va,U2 and V2,U: and V1 operate in synchronism and the change-over from one segment to the next always occurs at the: If the change-over switches are same instant. of the mechanical type they can be actuated by two synchronised driving apparatuses A and B switches at the provided with suitable gearing. The synchronisation can be achieved in any known manner:- for instance, by employing a periodically transmitted synchronising impulse. Naturally the ciphering and deciphering with elements of constant length can also be undertaken in such a whole multiple of the time of rotation of the other switch so the complete scrambling program only repeats itself after intervals which are greater than the period of rotation of each individual scrambling device in the apparatus.

In systems arranged for transmission in both directions special scrambling devices can be provided at each end for transmitting and receiving, as shown in Fig. 2, where the equipment of station I is designated by the numerals ll, l2, etc. and that of station II by the numerals 2|, 22, etc. The direction of the transmission is reversed by the manually or automatically operated change-over .switch R. The switch positions shown in full lines apply to a transmission from station I to station II whilst the dash lines indicate the positions when the direction of transmission is from II to I. The switches can also be replaced by fork connections or alternatively separate connections can be used for both direc:- tions oftransmission.

The arrangement illustrated in Fig. 3 indicates I how the same scrambling devices can be employed for both directions of transmission when the signals to be scrambled and the received signals are passed through the scrambling devices in the same direction. In this case the complete scrambling keys for both directions of transmission do not by any means correspond to each other because for instance the keys for S11 and $21 which operate with unequally long groups of elements cannot possibly be associated. With the arrangement shown in Fig. 4 it is, however, posinstance a gramphone record and then picked up and deciphered when desired. This new method is of course not restricted to scrambling spoken messages. Thesignals in question may also consist of impulses or tones such as are used in connection with telegraphy, teleprinting or other systems for the transmission of messages, orders and the like.

The various apparatuses which it is preferable to use for the scramblingsystem according to the invention are now described in greater detail by means of a number of constructional examples which are illustrated diagrammatically in the accompanying drawings.

Hitherto in order to minimise the risk of unauthorised deciphering as much as possible it has been necessary either to have a very long retardation time or a short retardation time and a large number of different running periods for the time-delay device. This, however, is a considerable disadvantage and prevents direct communication in two directionssuch as is required for telephone services. It is therefore one of the objects of the invention to provide a transmission system which enables these disadvantages to be overcome and at the same time guarantees that the possibility of the transmitted signals being deciphered by an authorised person is extremely remote, the retardation times being kept sible when reversing the direction of transmission also to reverse at the same time the sequence of the individual scrambling devices S11. $12 or E11, E12, so that for instance the first transmitting key operates in both directions of transmission with equally long groups. Since the key numbers associated with each other do not usually coincide, the complete scrambling programs for both transmitting directions will also not coincide.

The entire apparatus can also consist of a number of scrambling devices with reversible direction of transmission, as shown in Fig. 5. In

this event the complete scrambling programs co-' very short and the time-delay device itself very simple. Furthermore in proportion to the running period it is possible to obtain an extensive scrambling of the sequence in which the signal elements succeed one another. This is achieved by the use of. the following arrangement. The time-delay device possesses connections for m different running times, these diflering from each other by an integral multiple of I/nth the period of rotation of the switch. device and furthermore so dimensioned that the. diiference between the longest and the shortest running time is not greater than (3n-1) times the duration of one period of rotation of the switch device. The switch device is provided with n connections which are periodically switched in one after the other and the number of which is at least equal to the number of retarding times m. The scrambling key is so constructed and located between the m connections of the time-delay device and the 12 connections of the switch device that by means of the key each of the n connections of the switch device can be connected as desired with the m connections of the time-delay device.

which, when the short switching intervals be-- tween two successive contact segments are neglected, is equal to l/nth of the duration of one complete revolution of the switch arm 5. In the constructional example shown in Fig. 6 six contact segments are provided so that in this case n=6. The arrow shown on the switch device indicates the direction of rotation of the switch arm 5. The contact segments 6 are connected by means of leads with the key 3 which latter consists essentially of a network comprising two groups of conductors. One of these groups of conductors possesses n conductors which are connected as shown with the contact segments 6 of the switch device 2. The other group possesses at the most n conductors and in the example illustrated only conductors which lead to the terminals 1 on the time-delay device i. At the points of intersection of the conductors, contacts are provided by means of which each conductor connected with the time-delay device I can be connected with each conductor which leads to the switch device 2. If the number of conductors connected with the switch device 2 is indicated by n and the number of conductors connected with the time-delay device I is indicated by m, there will be nXm points of intersection and an equal number of contacts. The terminals on the retarding device are thus selected so that none of the m retardation times differs from the remaining Ones by the duration of a rotation of the switch device. It is preferable if the m retardation times form an arithmetic series where each is greater than the preceding one by l/nth of a rotation of the switch device. Furthermore it is expedient that the number of retardation times should equal the number of contacts on the switch device which are successively switched in. Thus m is selected to be equal to n so that the key 3 has n contacts. In order to obtain a faultless transmission of the signal and to be able to adjust the ciphering positions easi1y,.the scrambling key 3 comprises two groups of conductors, the first group consisting of n conductors leading to the switch device and the second group consisting of m conductors leading to the terminals 1 of the time-delay device. These two groups of conductors are arranged as already mentioned in the form of a network with mXn intersection points where contacts are provided,

as indicated by the circles shown in'Figs: 6 and 7. As shown in Fig. 6 the n conductors which form the network lines in one directionand are connected with the segments of the switch device,

are arranged within the ,range of the network in the order in, which the segments 6 offthe switch device are successively switched in; Similarly them conductors of the second group, which leadto the terminals I of'the retarding device a e arranged according to the graded running times. If then (m nl') diagonals are drawn through the m n contacts, 'as indicated by the dash-dot lines, the following conditions will be obtained whereby all ciphers can be determined with which a faultless transmission of the signal in question is possible. Exactly one single contact must be plugged in on each of the horizontal conductors leading to the switch device. Similarly there must be exactly one plugged-in contact on n of the (n+m-1) diagonals, whereby it should however be made impossible that for instance a contact is plugged in on the (n-l-x) diagonals counted from above when such a contact already exists on the :c diagonals, where :r is a whole number. It is therefore expedient to adopt special measures, such as mutual mechanical interlocks, to prevent this and ensure that the aforementioned rules. are adhered to. The scrambling key becomes very simple and clear if it is constructed as shown in Fig. 7. Thearrangement shown in Fig. '7 is obtained from that shown in Fig. 6 by means of the following transformation: The arrangement of the individual contacts shown in Fig. 6 is kept fixed and all contacts lying on the (n+1) to (1z,+m1) diagonals are displaced 21. contact spaces to the left so that the original (n+:i:) diagonal now forms the continuation of the a diagonal. The aforeas follows. applied to the terminal 4 of the'switch device" tact must be closed on each of the resulting diagonals with m contacts each and on each of the 1:. horizontal conductors leading to the switch de-- vice. A complete key thus always consists of n closed contacts.

Under the above conditions it is possible to employ the arrangement shown in Fig. 6 either for transmitting or receiving. Furthermore there are two fundamentally difierent operating methods when it is assumed that the direction in which the retardation of the signal elements occurs is always the same. This direction is indicated by the arrow shown on the time-delay device l of Fig. 6. The signal which is to be ciphered can enter the apparatus at the terminal 9 and is first of all retarded. After being subjected to various retardation times the complete signal passes over the m terminals of the timedelay device I and'over the scrambling key 3 to each of the contact segments 6 of the switch device 2. At each of the contacts 6 the signal has a difierent retardation time,that is to say it reaches each of the contact segments with a difierent delay. The actual retardation times are determined by the connections with the terminals I on the time-delay device I, whilst the sequence of the retardations at the contacts 6 is determined by the manner in which key contacts are plugged in. The switch arm 5 of the switch device 2 takes only I/nth of the signal at each of the contact segments 6 so that the signal is divided into elements the duration of which is.

which is being used. It is thus possible for signal elements which were originally next to each j other to be so displaced that the interval of time between them is equalto the difference-between the longest and shortest retardation time.

The second method of operating the appa-' ratus shown in Fig. 6 for scrambling signals is The message to be ciphered is first 2 and is thus first divided into equal elements which reach the terminals 1 of the time-delay device according to the key used. The elements are then subjected to the required retardation and are received at the terminal I]! in scrambled sequence. Faultless transmission is also assured in this case if the conditions already referred to are fulfilled. It can also be shown that these two methods of operation are also possible if the ciphered message is to be deciphered by means of the apparatus shown in Fig. 6. The scrambled signa1 can thus either be applied to the terminal 9 and received at the terminal 4 in deciphered form or applied to the terminal 4 ciphered and received at l0 deciphered. Depending upon the connection of the transmitter and receiver it may under certain circumstances be necessary to plug in a different key'in the receiver, or change-over connections must be provided for the key which enables this change over to be accomplished automatically as soon as the apparatus has to operate as a receiver instead of a transmitter. Connections for the transmitter and receiver, which are particularly suitable for intermittent both-way operation are described later by means of the arrangements shown in Figs. 9 and 10.

The construction of the key, time-delay device and change-over switch is now described in greater detail. Th time-delay device I can consist of an acoustic tube in which at the point 8 the signal to be transmitted is transformed into sound waves which at the terminals 9 after a certain running time are transformed back into electrical oscillations by means of a microphone.

- It is also possible to arrange sound transmitters at the terminals 1- which send sound waves through the tube in the. direction indicated by the arrow (Fig. 6). A microphone is then located at the point II which converts all the sound waves into electric oscillations. This acoustic time-delay can be replaced by a purely electric time-delay. For instance a large number of low-pass filters'connected in series can be arranged between the terminals 8 and H, each terminal I being associated with a definite number of these filters. The time-delay is then equal to the running time through these filters. An acoustical or electrical time-delay is, however, not very suitable for the scrambling device according'to the invention because it is difiicult to obtain the necessary exact synchronous operation of the-switch device in relation to the different running times and to maintain this synchronism for longer periods. It is therefore best if the time-delay device consists of a mechanically actuated signal carrier on which the transmitted message is recorded and then reproduced after the required intervals of time. The signal carrier can be a film on which the signals are recorded mechanically and reproduced photo-electrically. It is, however, preferable to use a device such as that shown in Fig. 8 where the time-delay device comprises an endless steel tape I which is actuated by the roller l2. The roller I2 is rigidly coupled to a driving motor l3 and the gearing I4, which latter drives the switch device 2. A steel tape time-delay device oii'ers advantages because it is possible to remove the message from the tape very simply by means of a wiping head l5 after it has been delayed and to render the tape ready for a fresh recording without having to interrupt its motion. Steel tape time-delay devices can either operate with two pole or single pole heads for recording and reproducing the signals. It is, however, preferable to employ single pole heads for the keying devices according to the invention. The single pole heads both for recording and reproducing the signals consist'of a coil surrounding a ferromagnetic pole piece which is in sliding contact with the steel tape, as shown in Fig. 8. These pole pieces are so constructed that they can be used equally well for recording or reproducing. When recording a message on the tape a direct current-source is connected in series with the magnetising coil so that the recording head is given the desired initial magnetisation. The heads 1 shown in Fig. 8 then function either as recording or reproducing heads according to the direction of transmission forwhich the scrambling apparatus is connected.

The"head' 8' is'used solely for recording whilst the head II is employed only for reproduction purposes, The distances between theheads I compared with the speed 1 of the steel tape I are then fixed so that n 'd'=v s p; n being the n'u'mber'of contacts on' t he switch device, 8' the duration of a rotation of the switch device and 1) any positive whole number which for'the successive distances between the heads is expediently selected to be equal to unity. The individual retardation times then form an arithmetic series.

The key 3 is constructed in the same manner as that shown in Fig. '7, the number of conductors connected to the switch device being equal to the number of conductors leading to the t1me-delay device. In the constructional example shown in Fig. 8 m is thus selected to equal n so that the key 3 thus has n contact points, in. this case 16. The arrangement shown in Fig. 8 diiiers from that in Fig. 7 in so far as the inclined diagonals of Fig. 7 are now arranged vertically and are omitted from Fig. 8 for the sake of clearness. The connections between the contacts on the key and the time-delay and switch devices are, however, unchanged. For the practical construction of the key 3 it is preferable to provide it selector switcheseachhaving n contacts which are so arranged that all the contacts in one horizontal v linecan be switched in one after the other in the desired order by the selector switches. If the 71 positions on each selector switch are numbered in acontinuous sequence an index having n numbers will be obtained which characterises the selected key position. The aforementioned conditions thus show that each number may only occur once in the index if the scrambling is to be free from errors. This system with selector switches is preferably also provided with electro-magnetic relays which automatically wipe out the key number as, soon as the scrambling device is switched out or if a disturbance occurs.

The switch device can also be constructed in a number of different ways. The mechanical switch contacts 6 can be replaced by electron tubes acting as switches. The switch 2 can also be designed as a capacity switch, the segments 6 being fixed condenser plates and the condenser plate attached to the arm 5 being rotated close to the fixed plates thus splitting up the signal into individual elements. Coils can also be employed instead of the contact segments 6, th coil axes being arranged according to the switch axis. It is then possible to obtain an inductive connection by meansof a coil fixed to and moved by the arm 5. In the mechanism described above it is preferable to replace the contact segments 6 by cam operated switches each comprising two stationary spring contacts which are switched in one after the other by means of a rotating disc provided with a cam.

It is often required that an apparatus of the kind shown in Fig. 6 or Fig. 8 should either be used to cipher a signal or to decipher a scrambled signal. Once the key has been plugged in it shouldremain unchanged for both cases, furthermore in order to obtain a short change-over time the direction of rotation of the signal carrier should remain the same. The change-over connections can be reduced to a mini-mum if an additional recording head 8 is located in front of and an additional reproducing head i i is located after the m reproducing and recording heads 1 respectively, shown in the arrangement illustrated in Fig. 8. The switching over of the apparatus is explained now by means of the arrangements shown in Figs. 9 and 10, where I and II are the same apparatuses as these shown in Figs. 6 an'd8. For the sake of clearness only the relevant terminals l0, 9 and t are indicated. Both apparatuses, each of which can be used for operating in either direction, are connected by means of a trans mission channel l6. This transmission channel Hi can consist of an ordinary wire conductor, for

instance a telephone cable, or sections of the transmission channel canalso be operated by .wlreless means. Each apparatus I and II is for instance equipped with a microphone il, a receiver i8 and a change-over device 19. In one end position of the change-over device the apparatus functions as a transmitter and in the other end position as a receiver. When the apparatus I and II is therefore being employed for intermittent both-way transmission the change-over device for the one apparatuswill be in one end position and the change-over device for the other apparatus in the other end position. Under these conditions a number of the described apparatuses can be connected to the conductor I G if it is desired to establish a multiplex system.

With the arrangement shown in Fig. 9 the change-over device it is located on the terminals ii and iii and switches in either the microphone it or the receiver 18 in the apparatus I and II. The transmission channel I8 is not changed over and lies between the terminals 6, that is between the switch devices of the apparatuses. The arrows in Figures 9 and 10 indicate the course of the signals through the apparatus and the transmission channel. The single arrows indicate that apparatus II is operating as transmitter and apparatus I as receiver, whilst the double arrows show that apparatus I is operating as transmitter and apparatus II as receiver. In Fig. 9 when receiving, the changeover device it causes the signal which is to be scrambled and is received by the microphone I! to be passed to the recording head in front of the m recording and reproducing heads Where it is recorded and delayed. The signal thenpasses by way of the reproducing heads to the key and the switch device. After leaving the sw tch device the signal is received in scrambled form and passes on to the transmission channel. When the apparatus is connected as a receiver the signal which is to be deciphered passes through the switch device and the key to the time-delay device and is recorded on the moving signal carrier in the correct order as regards time. The deciphered signal can thus be picked up by the reproducing head located behind the m recording or reproducing heads and passed on to the receiver iii. The '01. heads of the apparatus shown in Fig. 8 thus function as reproducing heads when the apparatus is connected as a transmitter, whilst when the apparatus is operating as a receiver they are used as recording heads. The arrangement shown in Fig. 10 differs from that in Fig. 9 in so far as the signal is always recorded on the signal carrier in a ciphered form. In the transmitter the signal thus passes to the switch device, arrives at the terminal ill in a scrambled form and passes through the changeover device it to the transmission channel l8. In the apparatus which is connected as areceiver the incoming scrambled signal goes first to the terminal F1 on the time-delay device and arrives at the switch device deciphered. With the arrangements shown in Figs. 9 and 10 .it is of course assumed that the switch arms 5 (Figs. 6 and 8) in the apparatus I and II are simultaneously on the same contacts, that is to say rotate in phase. If the phase is the same in each case the sum of the running times from the head 8 to the first head I and also those from the last head 1 to the head i i are of no importance as regards the system of connections shown in Fig. 9. This is always the case when the signal is recorded on the signal carrier in the transmitter and receiver in an unscrambled form. These additional running times must, however, be taken into account when the arrangement shown in I over device are shown in Fig.

Fig. 10 is used and they must then be so fixed that their total time is equal to one period of rotation of the switch device or a multiple of same. In each apparatus these running times are so fixed that each of them amounts to f times half the period of rotation of the switch device, 1 having such values as 0, 1, 2, 3, etc. In the practical construction of the appara us it is essential to incorporate amplifiers. A comparison of Figures 9 and 10 shows that obviously three separate amplifiers should be employed, one

of which is either reversible or can be used for both-way transmission. with a steel tape timedelay device it is preferable to use only two amplifiers for each apparatus, one amplifier serving exclusively for amplifying the signal reproduced I -corded signal cannot be obliterated by simple means, this change-over system must be used under the conditions stipulated. The change-over from receiver to transmitter and vice versa is considerably simplified when signal carriers are employed where the signal can be erased by means of special wiping devices, such as is the case with steel tape recording. In Fig. 8 the elements 8, H and i5 are shown which according to the operating conditions function as reproducing, recording or wiping heads. When the head is used for recording it is essential to have a supplementary direct current supply which is connected in series with the low-frequency recording circuit and produces a suitable initial magnetization of the steel tape. The same element can also be used as a wiping head if its coil is only supplied with direct current which produces a magnetization above saturation point and thus wipes out the recorded signal. When the head is used for reproducing purposes no additional voltage sources are required and the currents corresponding to the magnetic recording can be picked up directly from the coil. Under these conditions the simplest form of changeover arrangement is obtained when the heads 8 and I I shown in Fig. 8 are used alternately as wiping heads and the head l5 either for recording or reproducing as thecase may be. Two such apparatuses togetherwith the necessary change- 11 where the terminals 9 and ill for the wiping heads and for the combined recording and reproducing head ii are indicated and the connections with they change-over device l9 shown. This change-over device l9 connects the battery shown in the drawing with either of the wiping head terminals 9 or 10.. The remaining elements have the same reference numerals as in Figs. 9 and 10. In the position in which the change-over device i9 is shown in Fig. 11 the apparatus I functions as a transmitter and only the wiping head connected to terminal in removes the signal recorded on the signal carrier, the wiping head connected to terminal 9 remaining out of action. In apparatus II which operates as a receiver the ar-- rangemeni; is reversed and only the terminal 9 is intermediate signal Zq by scrambling according elements are recorded on ti. to the first partial key form of a variable magneti:

I I the first scrambling program 3 1 4 2 l I with the aid of one of the keying devices already 3 1 4 2 described, this intermediate signal being scramalready fixed in connection bled a second time by means of a further keyintermediate signal Z accord ing device and according to the second partial ship (4) could now be pickei key head located on the steel ta I, I ever, a number of receiving i 2 4 1 5 3 provided, which are connects signals which are twice scrambled in this mints the key 81 manner can be kept secret much better because switch segments the sewn in order to decipher them it i necessary to know g i that the Voltages both partial keys. According to the invention e colsi of theireceivmg hea this advantage can be achieved with the use of :fi rece outgoing one time-delay device K only because th unfinal signal (5) is new ciphered signal is passed by means of the gz' Produced b1 switching devices Hi and H2 over the various o e in i Sig! pply and receiving organs to the same timee secmd partial key delay device. The outlay for amplifiers, delay I I devices and the like i therefore considerably 2 4 1 5 3 smaller than if two separat scrambling appa- The magnetic recording i er; ratuses are used and the noise level is also much head B, so that the steel ta improved. fresh recording. The key sysi Signals which according to this method have f u 6 b eplaced by other been twice scrambled can be deciphered by means c nnecting the switch segmen: of two scrambling devices connected inv series, and receiving heads in any de whereby the first device supplies the intermedi- A S l W h as been 0111 ate signal Zq which is obtained from the signal e pp s o n in F g. 13 Zz and the second device produces the original by means of an identical appa signal Z1 from the intermediate signal Zq. In ingly adjusted and running syi accordance with the invention the signal can, reverse direction, the scramble however, be deciphered by using a single timet oduced at terminal 2 and r4 delay device K to which the scrambled signals at terminal I. In this second: are supplied through a first switching device and t pe h s oves past the heads taken off through a second switching device. A similar apparatus .is illus The switching programs for both switching de- The magnetic steel tape is mou vices must of course correspond to the two para rotatin Wh ely means tial scrambling programs on the transmitting vice Hi. the signal Z1 which i side. A signal which has been ciphered by according'to a first partial key means of the apparatus shown in Fig. 12 can for 110 the recording ds B11 to instance be deciphered by means of an identical the signal in the form of a, a apparatus when the ciphered signal is fed into 5 tiOn- The electric a es int the apparatus at the terminal 2 and the deof the receiving heads B21 to ciphered signal picked up at the terminal I, the terminal 2 in the order determi signal elements which pass through the organs Switch Hz. The magnetic reco. 2i to 25 to the time-delay K moving with a speed means of the W p n head Bi 'u from right to left to the receiving points i l to nected to a supply b e y thro Hi. When the switching devices Hi and H2 on The appa a u h wn n F i the transmitting and receiving side respectively used for deciphering without 1 operate in synchronism and according to the the direction of rotation, if the same program. then the signals passing the point is d in ou h th termini q---.gy and fed into or picked up at the terminal i ciphered signal taken oil at t] coincide on the transmitting and the receiving which case the switch R is cha side, that is to say the original signal transmitted the wiping magnet .32 instead is obtained at the receiving end. operation. This simple ch: Fig. 13 shows a device whereby the signal stor-' "scrambling, to deciphering' age is accomplished by magnetic recording. A favourable when it is desired to steel tape c is driven at a constant speed c by a transmission, because the sam motor M past the recording heads Bii to 314 the then be used'without any com receiving heads 3321 to B25 and the wiping head B. over from transmitter to receivi The signal which is to be scrambled passes over being used for both directions 0 the ingoing terminal 8 to the switch Ui which is .The change-over switches U also driven by the motor M and connects the indescribed above can be so con. going conductor in turn with the various vertical tated that the time interval conductors of the first keying system A1. These switch positions of the switch vertical conductors are plugged in at the contacts interval T2 between two switch determined by the first key number so as to conswitch U2 is in both cases equal. nect them with the diagonal conductors which suitable phase adjustment for I lead to the coils of the recording heads B11 to B14. it is possible to arrange that thl According to the contacts plugged-in in Fig. 13 a, b, c, (1, etc., whose length is connection is established in turn with 12, B11. recflrdlng are ot subd vided B and B12, that is to say the individual signal picked up by the receiving he:

:y, the terminal I!) for the eing disconnected. The 6 remains unchanged and l to the terminal ,4 of the apparatus. As in the case ted in Fig. 9 the suppleiing time in each apparalce because obviously the the steel tape in an un- 1 the arrangement; shown a very simple matter to over the amplifiers if only vided one of which serves the alternating current dcked up. The amplifiers up either in front of the he terminals 4, depending are intended to serve..

illustrated in Figs. 6+11 identical apparatuses are arating a steel tape time- .he disadvantage that the ed must be recorded and mes. When for instance ltuses are employed it is vide three separate steel ther development of the en possible to avoid this 1e same time retain all the iltipl scrambling system. is the signal elements the o be scrambled in accordiodically recurring partial different supply organs iese organs being characrunning times, and the re picked up through difs of the same storage de- .th a second partial properiodically different inorgans being also characinning times. Thus it is successive partial scram- Eerent programs with the :e device and without too' ng necessary.

ambling is now explained the constructional exam- 12-15 of the accompanyants the first switching deh the ingoing conductor l various supply leads I l, -delay device K in accordremains the sam from group to group.

al program. In the time-- a1 elements move with a the various supply points A second switch dethe outgoing conductor 2 partial program with these Jresent the length with re- I icoming and outgoing elelat is to say-the interval switch segments of the switch devices H1 and H2. Since the unused incoming and outgoing organs can be omitted it is also possible that the distance between two remaining adjacent leads may amount to an integral multiple of D1 or Dz respectively. 1

The signal to be scrambled Z1=abcdefghiklm (3) consisting of the "elements a, b, 0, etc, each of equal length, is now passed to the incoming conductor I. For instance four successive elements of this signal form a group, the switching-over in H1 being accomplished in a sequence which Ac-- cording to a first four-figure key the switching-over should for instance occur in such a manner that the signal elements which travel with a speed 22 from left to right through the time-delay device pass the point q-q in the following order: The first element a will now occupy the third place in accordance with the key number 3, the second element 1) as result of the second key number provided with a stroke couples the (1+4) =fifth place, the third element 0 as a result of the third key number 4 occupies the fourth place and the fourth element lies as a result of the key number in the (2+4) =sixth place. The elements of the second and following groups are delayed in an analogous manner. This is achieved by connecting the ingoing conductor i in turn by means of the switching device Hi with the supply organs ll, I2, l3, etc. The signal elements pass ing the point qq represent a first partial scrambling of the original signal Z1. If a special receiving device were located at the point q-q .it would thus be possible to picls up the scrambled signal:

Z a.c bdegfhillcm... (4)

The signal which has been subjected to simple scrambling is, however, not picked up at this point but taken from the device K through the receiving organs 29 to 25 and the switching de vice Hz after a further scrambling. The signal is taken from the time-delay device for in stance according to a second key organs 24, 22, 2d, 23, 22. Instead of the signal Z11 the following signal is received at theterminal 2, this signal result- 'ing from "a double scrambling of the original ingoin'g signal Z1. The signal Z2 is thus produced from the signal Z1 by first obtaining the scrambled signal Z2 also consists of such elements a, b, c, d, etc., and not fractions of same. This condition has been assumed for instance in connection with the description given of the arrangement shown in Fig. 12 but must not always be so. The length of the elements determined by the switch U1 can, however, be subdivided by the switch U2 if this latter is rotated with a difi'erent phase position or operates with a time interval T2 which differs from T1. Even in such a case it is of course possible to decipher the signal which has been scrambled according to the method described, if the change-over devices at the receiving end operate with corresponding phase adjustment and change-over frequency.

In order to increase the secrecy of transmission the apparatus according to the invention can be connected in series with other scrambling devices so that a multiple scrambling system is formed. The easiest and simplest form of multiple scrambling system can be obtained if several double-scrambling systems of the kind described above are connected in series. In Fig. an arrangement with two double-scrambling apparatuses E1 and E2 connected in series and having an intermediate amplifier v, is shown diagrammatically. If the apparatuses E1 and E2 are such that when the direction in which the signal passes through the device is reversed the signal is deciphered, the arrangement shown in Fig. 15 can be used either for scrambling or deciphering as desired, the signal passing either from left to right or vice versa. To correspond to the direction in which the signal is being transmitted it is essential to change over the connections of the amplifier v by means of the switches R1 and R2.

When a number of scrambling systems are connected in series it is advisable to employ apparatus in which the period of rotation of the switches difiers from each other so that the complete scrambling program repeats itself after time intervals which are longer than the period of rotation of the individual scrambling devices, unauthorized deciphering being thus made considerably more dificult.

The magnetic time-delay device shown-in Figs. 13 and 14 can of course be replaced by other known kinds of time-delay devices. The device K in Fig. 12 can for instance consist of a tubular acoustical retarding device with suitable loudspeaker systems located atthe supply points H to l4 and microphones at the picking-up points 2i to 25. It is also possible to use an electrostatic recording system with a moving insulated member or optical recording combined with photo-electric cells for picking up the signal ele- 'ments by means of a variable transparent signal carrier. v

The switch devices for the variable recording and receiving of the signal elements can consist of electrically operated mechanical switches with sliding contacts or cam contacts. The ingoing and outgoing conductors to the recording and receiving heads can, however, also be provided with electric valves which are electrically controlled in accordance with a fixed program. For this purpose dry rectifiers or electron tubes can for instance be used, these being rendered intermittently conductive by means of short control impulses. The switching-over process can also be accomplished by means of cathode ray tubes the ray of which is diverted by a number of mutually insulated electrodes which are connected in the desired sequence with the various recording and receiving organs of the time-delay device.

We claim:

1. A method of sending and receiving signals in cipher which comprises subjecting a signal in succession to a plurality of substantially continuous time-delayed scrambling operations in each of which the order of elements of the signal is transposed in accordance with a preselected recurrent program to produce a multiscrambled signal, transmitting the multiscrambled signal, and subjecting the received signal to a plurality of successive, substantially continuous scrambling operations corresponding in number to the number of scrambling operations and in each of which the order of elements of the signal is transposed in inverse relation to the transposition efiected in the inversely corresponding scrambling operation.

2. A method of sending and receiving signals in cipher which comprisessubjecting a signal in succession to a plurality of substantially continuous time-delayed scrambling operations in each of which the order of elements of the signal is transposed. in accordance with a preselected periodically recurrent program, the number of signal elements in the period of said recurrent programs being difierent in each successive scrambling operation, to produce a multiscrambled signal, transmitting the multiscrambled signal, and subjecting the received signal to a plurality of successive, substantially continuous unscrambling operations corresponding in number to the number of scrambling operations and in each of which the order of elements of the signal is transposed in inverse relation to the transposition effected in the inversely corresponding scrambling operation.

3. A method of sending and receiving signals in cipher which comprises subjecting a signal in succession to a plurality of substantially continuous time-delayed scrambling operations in each of which the signal is divided into a plurality of signal elements of equal length which elements are then transposed according to a preselected periodically recurrent program to produce a multiscrambled signal, the numbers of elements comprised in the recurrent periods of each scrambling operation having no common factor other than unity, transmitting the multiscrambled signal, and subjecting the received signal to a plurality of successive, substantially continuous, unscrambling operations corresponding in number to the number of scrambling operations and in each of which the order of elements of the signal is transposed in inverse relation to the transposition eii'ected in the inversely corresponding scrambling operation.

4. A method as defined in claim 1 in which the length of the signal elements of one scrambling operation is an integral multiple of the length of the signal elements in another scrambling operation and in which the periodicity of the program of said one scrambling operation differs from the periodicity of the program of said other scrambling operation.

5. A method as defined in claim 1 in which the length of signal elements of any one of the scrambling operations bears no rational relationship to the length of the signal elements of any other of the scrambling operations.

6. In a secret signalling system in which 59-- crecy is obtained by 'transposing components of the signal to produce a scrambled signal for transmission, the method which comprises sub- Jecting the signal to a plurality of scrambling operations in succession, each scrambling operation including the division of the signal into a plurality of elements and the elements of successive scrambling operations being of diflerent magnitude.

7. In a secret signalling system in which secrecy is obtained by transposing components of the signal to produce a scrambled signal for transmission, the method which comprises subjecting the signal to a, time-delayed scrambling operation in which the individual signal elements of recurrent groups of signal elements we transposed .to produce a scrambled intermediate signal, and subjecting the scrambled intermediate signal to at least one additional scrambling operation.

8. A method of sending and receiving signals in cipher which comprises dividing the signal on a time basis into recurrent groups of signal elements, subjecting the several elements of each group to unequal time-delays to develop a scrambled intermeoiate signal in which the order of the elements of each group is transposed in accordance with a preselected program, dividing the scrambled intermediate signal into recurrent groups of signal elements, subjecting the several elements of each group of the scrambled intermediate signal to unequal time delays to develop a multiscrambled signal, transmitting the multiscrambled signal, subjecting the transmitted multiscrambled signal to an unscrambling operation to produce a received intermediate signal duplicating the scrambled intermediate signal, and subjecting the received intermediate signal to an unscrambling operation to produce a duplicate of the original signal.

9. Apparatus for sending and receiving si nals in cipher including a transmitter and a receiver, said transmitter comprising a plurality of scrambling devices through which the signal is transmitted in sequence, each of which scrambling devices includes means for dividing the signal into a plurality of elements and means for transposing said signal elements according to a preselected recurrent program, said receiver comprising a plurality of unscrambling devices equal in number to the number of scrambling devices of the transmitter and through which the signal is passed in sequence, each of said unscrambling devices including means for dividing the signal into a plurality of elements and means for transposing said signal, elements in inverse relation to a corresponding scrambling device of the transmitter, said unscrambling devices being arranged in inverse order to said scrambling devices with respect to the direction of signal travel therethrough, and means for synchronizing the operation of said transmitter and said receiver, whereby the signal is scrambled in the transmitter, transmitted in scrambled form, and unscrambled in the receiver to reproduce the original signal.

10. A device for scramblirm and unscrambling a signal which comprises a continuous signal carrier, a substantially continuously operating timing device for dividing a, signal in transit on said signal carrier into recurrent groups of signal elements, means for conducting signal elements between a plurality of positions on said signal carrier and a plurality of sections of said signal divider, thereby providing a plurality of paths between each of said positions and each'of said sections, and means for selecting a unique path between a carrier position and a divider section for each successive signal element in a predetermined group of elements.

11. A device for scrambling and unscrambling a signal which comprises a magnetizable tape, switch means for dividing a signal into a plurality of elements in accordance with a preselected program, a plurality of 'electromagnets 1n magnetizing relation to said tape, means for con ducting signal elements between a plurality of sections of said switch means and said plurality of electromagnets, said conducting means providing a plurality of paths between each of said sections and each of said magnets, means for selecting a unique path between a section of said switch means and a magnet for each successive signal element in a predetermined group of elements, and means for translating said tape past said magnets.

12. A device as defined in claim 11 wherein the means for conducting said signal elements between said switch means and said electromagnets includes a network of two groups of conductors of which one group comprises leads from the several terminals of the switch means and the other group comprises leads from said plu-,

rality of electromagnets and said selector means includes means for connecting any of the first group of leads with any of the second group of leads.

13. A device as defined in claim 11 in which said switch means is a rotating switch for dividing the signal into' a plurality of equally long elements, said magnetizable tape is endless and is translated at constant velocity, said electromagnets are equally spaced along said tape, and in which a common driving means is provided for rotating said switch and for translating said tape according to the following relationship in which n is the number of switch elements of said switch means, d is the distance between adjacent electromagnets, 12 is the velocity of said tape, 8 is the period of rotation of said switch means, and p is any positive integer, said endless tape being further provided with means for obliterating magnetic impressions thereon at each cycle of the tape.

14. A device as claimed in claim 11 wherein said switch means includes a plurality of switch elements each comprising opposed contact springs, said switch elements being actuated in sequence by a rotating cam driven in timed'relation to the velocity of translation of said tape.

15. A device for scrambling and unscrambling a signal which comprises a continuous signal carrier, a substantially continuously operating signal divider, means for conducting signal elements between a plurality of positions on said signal carrier and a plurality of sections of said signal divider, said conducting means providing a. plurality of paths between each of said positions and each of said sections, means for selecting a umque path between a carrier position and a divider section for each successive signal element in a predetermined group of elements, a second substantially continuously operating signal divider having a different number of sections than said first mentioned signal divider, means for conducting signal elements between said plurality of positions on said signal carrier and a plurality of sections of said second signal divider, said second conducting means providing a plu'-' rality of paths between each of said positions and each of said sections, and a second means for selecting a unique path between each of said positions and each of the sections of said second signal divider for each successive signal element in a predetermined group of elements.

16. A device for scrambling and unscrambling a signal which comprises a magnetic tape, switch means for dividing a signal into a plurality of elements in accordance with a preselected program, a plurality of electromagnets in magnetizing relation to said tape, means for conducting signal elements between a plurality of sections of said switch means and said plurality of electromagn'ets, thereby providing a plurality of paths between each of said sections and each of said magnets, means for selecting a unique path between a section of said switch means and a magnet for each successive signal element in a. predetermined group of elements, a second substantially continuously operating switch means having a different number of sections than said first mentioned switch means, a second plurality of electromagnets in magnetizing relation to said tape, means for conducting signal elements between a plurality of sections of said second switch means and said second plurality of electromagnets, thereby providing a plurality of paths between each of said sections and each of said magnets, a second means for selecting a unique path between a section of said second switch means and one of said second plurality of magnets for each successive signal element in a predetermined group of elements, and means for translating said tape past said two groups of electromagnets.

1'7. A device as defined in claim 16 in which the means conducting the signal elements between each'switch means and its respective plurality of electromagnets includes a network of two groups of conductors of which one group comprises leads from the several terminals of the switch means and the other group comprises leads from the plurality of electromagnets and means for connecting any of the first group of leads with any of the second group of leads.

18. A device as defined in claim 16 in which a common source of power is'provided for driving said switches and said tape in preselected timed ratio, and in which said tape is endless.

19. A device as defined in claim 16 in which said magnetizable tape comprises the periphery of a rotating wheel, said sets of electromagnets being disposed about the periphery, and in which means is provided between said sets of electromagnets for obliterating magnetic impressions upon said tape.

20. A device as defined in claim 16 in which both of said switch means include electrically controlled valves for controlling the transmission of the signal elements to the different sections of said switch means. I

GUSTAV GUANELLA. WALTER ERNST. WERNER LINDECKER MARCEL GABRIEL.

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