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Àm@ 2?@ 194@ c». M_YÉRS SECRET SIGNALING Filed July l?, 1943 4 Sheets-Sheet l /22 /N VEN Tof? 0. MYERS A ïroR/w-v ‘ Ang@ 2279 ÍìÈf-’ÃQO‘ ` Q, MYERS SECRET 2,4@5353 » SIGNALING > Filed July l?, 19425 4 Sheets-Shes?, 2 FIG Ä OPERA TED CONTACT) 5 CODE PLI/G /NVE ¿YJ 0. MYERS A TTORNE V Ära@ 2”?, i945». „ o. MYERS '2,406,353 SECRET SIGNÀLÍVNG Filed July 17, 1945 4 sheets-sheet s Flc. _5 BY Q MYERS A Tron/Vey ì Äug. 27, 194, ' Q_ MYERS ` SECRET SVIGNALING Filed July 17, 1943 2,406,33 4 sheets-sheet@ /N By' v0. MYERS A fro/PNE y ` 2,406,353 Patented Aug. 27, 1946 UNITED STATES PATENT OFFICE 2,406,353 SECRET SIGNALING Qscar Myers, Mount Vernon, N. Y., assignor to Bell Telephone Laboratories, Incorporated, New `iZork, N. Y., a corporation of New York ' Application July 17, 1943, Serial No. 495,126 11 claims. 1 (Cl. 179-15) 2 The present invention relates to the trans mission of speech or other types of signals with privacy. The invention is based upon the use of variable time delay in transmission of signal elements to render reception of the message diiiicult. A known type of privacy uses a moving mag the record tape and these are designated A, B, C, D, E, F, G, H and I. If magnet A is used, since it is situated nearest to the recording magnet, a delay of one unit is introduced. Magnet B in troduces two units delay, etc. The above code, together with its decoding sequence, could be expressed in terms-of the electromagnets that netic tape with cooperating electromagnets spaced along the tape at equal intervals as a means of producing unequal time delay in the transmitting code then being A B C G F I-I C F D G E and the decode sequence being C B D GI D transmission of signal elements. A commutator or equivalent is used to switch electromagnets, serving as individual recorders or pick-ups, into are used in successive commutator times, the ` C G F E. The connections between the com mutator segments and electromagnets at the transmitter would have to be different from those» at the receiver if this code were.. used. This circuit with the line in definitely timed short intervals, A similar arrangement is used at the l5 would be satisfactory in the case of one-way receiver to decode the message. In such a sys tem the sum of the delay introduced at the trans mitter plus that introduced at the receiver is the same for all signal elements. For illustration, assuming a commutator of ten segments individ ually wired to the electromagnets, the total delay transmission or two-way transmission on a four wire basis using four machines. Two-way trans mission with two machines each serving alter nately to receive and transmit would also be possible with diiierent codes usedl for opposite directions provided the necessaryV switch-overs were made at both stations whenever the direc at both transmitter and receiver is ten units (a tion of transmission is reversed. In order to being in this case one tenth the rotational avoid the rather complicated switching that period of the commutator) so that if a delay of three units is introduced in transmitting a given 25 would be involved it has been proposed to use self-converse codes, meaning that if one ma signal element, a delay of seven units must be chine is set to code a message for transmission introduced for that element in the receiving and with a self-converse code, it can without switch decoding process. With a given wiring between over decode a received message sent with the commutator segments and electromagnets‘ the the code is repeated in each rotation of the com 30 same code.` This imposes the limitation that the delays introduced into the individual` signal ele mutator, “code” here being used to indicate the ments as transmitted must be the same as the scheme of time delays introduced in the ten in delays introduced into the elements as received, dividual signal elements sent in commutator and that as before the sum of the delays intro times l to lû, inclusive. This can conveniently be expressed as a series of ten numbers, for ex 35 duced into the same signal element at both trans mitter and receiver must be equalto that for each ample, i 3 7 5 8 3 5 Li 7 5 to indicate the delays of the other elements. One such code, for illus of the respective elements. In View of the fact tration, might be B G E G C F C E H D. that each-element must experience a total delay Applicant has found that for every self-con oi ten units at transmitter and receiver together, verse code a pair of electromagnets must be used, if the message is to be successfully decoded, the one giving a delay complementary to theY other, time delays introduced at the receiver in order and that `the commutator segments to which to decode the message sent by this code would these pairs are connectable also fall into pairs. have to be 9 '7 3 ¿i 2 '7 4 6 3 5 for the respective In the case of a ten-element code, the electro signal elements considered above, but since these elements are variably delayed they are actually 45 magnets andcommutator segments can be ar ranged in a table comprising forty-live possible received in a diñerent order from that which they pairs of electromagnets and commutator seg originally had, the received order being 3 5 4 2 1 ments. This fact enables a straightforward type 7 9 6 8 i0 on the basis of an original order of 1, of selection to be made for setting up all possible 2, 3, etc. Ifv the receiver delays given above are identiñed‘with the individual signalelements the 50 self-converse codes and gives the general pattern of a switching circuit for selecting the codes. receiver code expressed in terms of delay to be An object of the invention is to facilitate se introduced into the signal elements as received lection of diiîerent codes for both transmitting wouldbe32-47943765. and receiving and especially to provide for quickly In the known type of privacy system referred to there are nine electromagnets spaced alongV 55 and automatically changing codes. 2,406,358 3 The nature of the invention and its Various objects and features will be better understood from the following detailed description in conu nection with the accompanying drawings in which Fig. 1 is a table from which to determine interconnections between reproducer magnets and commutator segments in making upk Selin converse codes; Fig. 2 is a partial View in perspective of one , 4 relatively simple matter to arrange switching mechanism to select the codes one after another in any desired sequence. One such switch mechanism is shown in Fig. 2 and comprises a rotating cylinder 2Q with inn sets, two of which are shown at 2l and 22, ex~ tending the length of the cylinder and situated close together entirely around the cylinder. Each inset has five raised portions, which when di type of code selector according to the inven tion; and Figs. 3, 4, 5 and 6 when placed together in the manner shown in Fig. '7 show in schematic dia~ spring to be closed, as indicated, for example, at 25 and 26. There would be forty-five such springs gram form the circuit of a complete two-way 23 any ñve of which are operated at a time as rectly underneath corresponding springs 23, raise the springs and cause two pairs of contacts per privacy system in accordance with the invention. 15 determined by the positions of the lugs on any In Fig. 3, the magnetic tape is shown at II one insetrfrîl or 22, etc. One 'setpf contacts, 25, passing "overwpulleys I2 forY driving itY and the would connect a particular reproducer pick-up electromagnets are shown below the tape, there coil with a particular commutator segment I, 2, being nine reproducer magnets lettered A, 3,'etc., of the regular set. The other set of B . . .. I, a recording magnetV I3 and an eraser contacts, 25, would connect a particular pick-up magnet I4. Each of the reproducer magnets` is coil with a particular commutator segment I', adapted, by switching devices to be described, to 2', 3', etc., of the interlace set. `be connected to an individual segment of the The insets 2l, 22, etc., can be made of metal, commutator shown in developed form at the plastic, ñber or other suitable material and they 25 right of Fig. 3 with the segments in a vertical can be inserted in slots in the cylinder and can line. These segments are numbered I to II) and be readily interchanged among themselves by I' to _'I0’, the latter being interlaced with the .simplyl withdrawing them and reinserting them in former. In the drawings, these segments are diiïerent order. shown widely separated but in practice it will be The cylinder 2i! can be stepped to bring the understood that they would be situated as closely next inset underneath the row of forty-five together as feasible in accordance with usual switch springs 23 by means of a pavvl and ratchet _ commutator design. It will be understood that in practice the tape II may be mounted on the rim of a disc and that the commutator may be actuated at `timed intervals by a clock-operated operated by stepping magnet 3G which can be contact or from the commutator drive, as for circular and mounted so that the same shaft 35 instance, after each rotation of the commutator rotates the tape disc and the commutator brush or after a given number of commutator rota I5 over the segments. tions.V Reference will now be made to Fig. l which It will be understood that the insets are cut consists of forty-five boxes in each of which s0 as to select five pairs of magnets, and accom-v appears a pair of letters designating reproducer 40 panying commutator segments from those given magnets and an associated pair of numbers des in the table of Fig. l to provide self-converse ignating commutator segments. vThus, in the codes as previously explained, each strip with its single’boX appearing at the top of the figure, the lugs representing one code. The interlace code notation indicates that if reproducer A is con can be entirely independent of the regular code. nected to commutator segment 2 and if repro 45 Reference will now be made to Figs. 3, 4, 5 and ducer I is connected to segment I , two of the 6 arranged as shown in key Fig, '7. It will be signal elements of a ten-unit section of signal noted that forty-five relays are shown in Figs. will be coded in a self-converse code. The two 5 and 6 arranged in the same manner as the signal elements sent by such arrangement will be boxes in Fig. l, except that for co-nvenience of correctly decoded at the receiver with identical 50 arrangement on the sheet the table is turned on connection of reproducersA and I to the commu its Vside in Figs. 5 and 6 with the relay corre-= tator segments 2 and I thereat, assuming, of spending to the uppermost box in Fig. 1 shown course, synchronous operation of the machines. , at the extreme right in Fig. 6. The bottom row ’ A complete ten-element self-converse code can of boxes of Fig. 1, therefore, corresponds to the be built up by choosing any rive boxes that re vertical column of relays at the left side of Fig. 5. Each relay has two armatures and it will be ob sult in a connection to each of the ten commu tator segments with only one connection to each served that the armatures are permanently oon segment. There may and usually will be more nected to commutator segments and when at tracted close contacts leading to the pick-ups. than one connection to the same reproducer. It will be noted that in any self-converse code, 60 Taking the left-hand column of relays of Fig_ 5, such as that given earlier in this description by for example, and reading from the tcp down, the left armatures are connected to respective com ' way of illustration, the letters representing _the mutator segments I, 2, 3, e, 5, 6, 1, 8 and 9 while amount of delay given to a signal element appear the right-hand armatures are all connected to in pairs such that the sum of the delays is the same for all pairs. Moreover, the letters corre 65 segment I0, A corresponding rule with one less total number is followed in each of the other spond in their position in the code to com columns of relays. Again `considering the left mutator segments and, in the case of each pair, hand column, the left armatures can be closed are separated by a number of segments equal to to Vconnect individually to reproducers A, B, C, the number of delay units represented by oneV of etc., reading from the top relay down, while the the pairs, counting around the commutator re 70 right-hand armatures have an opposite order of garded as a closed ring. connection, that is, they can be closed to con Since these fort’y-iîve sets of connections rep nect individually to reproducers I, H, G, F, E, D, resent all of the possible self~converse codes when C, B and A. A similar scheme is followed in the taken five at a time as explained,` it becomes a 75 GEES@ Oi the other columns except displaced one .23406;3532 5 reproduc'erY element since the number of relays decreases’byA one per co-lumn. It‘ willlbeî seeni by tracing' out the wiring that whenever a particular relay is energized it con nects- Vie pair of picl§~ups to the pair of com mutator segments that are given in the corre sponding box. in Fig. 1. Taking relay G0 (Fig. 5), for example, which corresponds to the box marked 40 in Fig. 1, this relay when energized closes’` both its armature contacts, the left arma ture connecting commutator segment 4 to repro ducer‘D and the right armature connecting com For simplicity of drawing. onlyf‘a few connec tionssareshowniinlFig;14ibetween the energizing lea-ds: fori theirei'aysrinfFigs'. 51and16 and the selec to'rflíanksi. It.wil1 be'. obvious, however; how all of the' connections-î indicated inthe diagram of Figi: 1f can; be‘i‘provided'. for by ` merely connecting the individual.- leads’A from the code relays to A great 10 proper' ch’c's'enipointsî ofi the selectors. variety oficonne'ction'sïis' possible since the codes can’ be. seti uprsin~` any' desired sequence and the mutatorse‘gm‘ent Iâ'to reproducer F. It is merely same code can-bef-used over and over again in necessary, therefore, to energize five relays to pro vide av self-‘converse code, these relays corre spondin‘g»` to any suitable five boxes in the dia different sequences.'` 'Iîh’e‘sele'ctin'g circuit-‘of Fig. 4’ and the relays on Figs. 5 and ôrdetermine thecoding to be used for gramfof'Fi‘g. l. ' ' " ' Each relay in Figs. 5 and 6 has an individual energizing- conductor extending off the top of Fig. 5 to the selecting circuit in Fig. 4 where a ground can be applied to any of these leads, the opposite’ side of each relay being permanently the'normalcommutator'segments I, 2, 3 Y. . .,I0. A duplicate-set of’equipment is indicated in the upper part of Fig, 3 to determine the coding to be used' for’ the interlace set. of segments I', 2', 3"`. |0'~, this equipment' consisting of a tim ing and selector circuit IZI, which may be en tirely‘si'milar to that shown on Fig. 4, and forty ñve selecting relays (interlace set) |22 which may Referring to Fig. 4, two banks of selector switches are shown, those at the left being num 25 be similar to those shown in Figs. 5 and 6. 'I‘he wiring betweenfthe relays and selectors and the bered I0!)k to E05 and those at the right being wiring within the timing’and selector circuit in numbered |00 to III. The switches |00 to |05 the case-of thi’s'interlace equipment IEI, |22 may are `Steppe@ by stepping magnet I I2 and switches be‘different from’ that used in the normal set of |00? to III are stepped by magnet H3. 'I'hese switches are stepped under control of clock-op 30 equipment of Figs. 4, 5 and 6; since the normal and interlace codes can be entirely independent eratedV contacts H4 which when closed energize ofeachotlier. Also the Wiring between the re either stepping magnet H2 or H3 depending lays'andcommutator segments may be different upon whether or not the transfer relay H5 is in the’two- cases. energized or deenergized. This relay is, in turn, In the use of this equipment to transmit and controlled by the two selector switches |05 and receive, the telephone or other signal generating III‘I in tandem from ground H6 through contact means |3I and the telephone or other signal re of selector |00 through conductor leading through ceiving means |32 are arranged as in Fig. 3 to be the code‘plug H1. Contact of selector |06 and connected into the system by the two-position` winding of relay I I 5 to battery. It is to be under three-spring switch |30, which is shown in nor stood that a number of conductors extend bc mal'or receiving position. The “line” |33 may tween the sector of selector i 00 and that of selec bethe audio input to a radio or other signal tor |05 and that the code plug provides cross connected‘to battery as shown in Figs. 5 and 6. connections between these conductors as may be desired to introduce a variable operation into transmitter and theY audio output of a radio or other receiver, or it may be one side of an or relay M5L For example. with the relay H5 in 45 dinary telephone- or other signal line the oppo site side of which in any case is assumed to con the‘condition shown the next time contacts H4 sist, in' this figure, of grounded terminal of re are closed stepping magnet I i3 is energized caus corder coil I3 but may, if desired, be metallic. ing switches |00 to III to take an additional With switch |30 in the position shown, coded step. If after such step taken switches |00 and |05 find a closed circuit to ground, relay H5 50 speech' or other signall received over line |33 is sent tlt'irougl'i'centralswitchV spring‘of switch |30 . is energized but if no circuit to ground is closed and,` conductor I 35 tothe recorder coil I3 and in this position of switches |00 and |06, relay makes 'a record of coded speech or signal on the H5 remains- unenergized. The wiring between tape H. As different parts of the coded mate switches if??? and |05, together with that inside the code plug, may be such as to cause relay H5 ¿a Si rial is picked up by the coils A, B, C, etc_ the brush I5 is passing over the commutator seg to be operated or unoperated for varying lengths ments and momentarily connecting these indi of time. vidual coils inproper order to the receiver |32, Another transfer relay B20 is also operated in through the upper spring of switch |30, to decode parallel with transfer relay I l5. The purpose of relay IZiD' is to furnish grounds to the movable 60 the. messagethe order of connection being de termined by the yrelays in the regular and inter arms of either the selector switches |00 to |05 lace sets of selecting relaysV as previously de or |01 to III. With relay |20 unoperated as scribed. shown grounds are supplied to the wipers of se In transmitting, the talker or user pushes lectors |01 to HI. With the wipers in the posi switch |30 to its upper position so that the trans tions shown these grounds cause energization of mitter I3Il is connected to recorder coil I3 and the following relays on Figs. 5 and 6: I, I3, 26, the message is recorded on the tape I I in normal 35 and 40. These relays, in turn, set up the fol form, the coding taking place by the relays con lowing code using the notation given in Fig. l: A-2 I-l., C-G G-3, C__S Cif-5, B-9 H-7, F-lO D-4. If with the switches in the position shown the relay |20 were energized supplying grounds to the selectors 0n the left, the following relays in Figs. 5 and 6 would have been operated: 8, I9, necting Various ones of the pick-up coils A, B, C, etc. individually to the commutator segments and thence via brush I5 and middle switch spring of switch |30 -to the line |33. It is to be understood that various substitu 24, 29 and 42 and the following code would have 75 tions, alterations and modifications may be made 2,406,353 7 within the spirit and scopeof the claims, which follow. What is claimed is: 1. In a speech privacy system in which differ ent speech fragments are delayed in transmission -by different amounts of time, a plurality of in dividually actuable devices each determining a diiferent transmission delay time, a circuit and circuit contact for. actuating each device, said contacts being arranged in pairs, the devices con trolled by the contacts constituting any one pair determining respective transmission delays the sum of which is a constant, and means selectively operating said pairs of contacts. 2. In a privacy system in which a succession of delay elements is used to >introduce successive equal units of delay into signals together with means for allotting time periods to said elements for individual operation, means to code or decode the signal comprising switches associated to be always operated in deñnite pairs, each pair of 8 7. In a privacy system including a moving rec- ord medium for signals vand reproducers spaced along said medium, and timing means for divid ing the signals on a time basis, means to provide a plurality of paths between said reproducers and said timing means, switching means for clos ing said paths in predetermined pairs to produce time shifts in a pair of signal fragments such that the time shift in one fragment is the-.con verse of that in the other, and means to select groups of said switching means. 8. In a signal privacy system using a moving magnetic tape, electromagnets spaced therealong and a commutator having segments, for arrang-~ ing signal elements in different time sequences in cycles, switches associated in inseparable pairs, one switch of a pair when operated closing a cir cuit from one of said electromagnets to one oi said segments and the other switch of the pair 20 when operated closing a circuit from one of said electromagnets to a different oneV of said seg switches when operated determining a particular ments such that the time sequence, within a cy pair 0f delay elements to be used and particular cle, given to a signal element by closure of one time periods allotted to them for operation such of said circuits is the converse of that given by that the sum of the -delays introduced into sig closure of the other circuit, and means for selec nals by the two elements of the pair is a constant tively operating said pairs of switches in groups for all pairs and the time periods allotted tothe simultaneously. elements of a pair for operation are always sep 9. The invention claimed in claim 8 in which arated in time by a number of time periods cor said switches comprise electromagnetic relays, a responding to the number of units of delay intro» 30 selector circuit having successive positions, duced by one of the elements of the pair. l means in each position of said selector circuit-for 3. The invention claimed in claim 2 in which operating a group of said relays, and means to said switches comprise pairs of double contact move said selector circuit from one position to Y switch springs and cams for operating said pairs another. . individually and selectively. l l0. The invention claimed in claim 8 in which 4. The invention claimed in claim 2 in which said switches comprise pile-ups of pairs of said switches comprise sets of switch spring pile ups, each pile-up compri-sing two switch ele. ments, and means for actuating said switches _ springs and said meansforselectively operating» said pairs of switches comprises a rotatable cyl inder containing projecting lugs on its surface for comprising a rotating drum and -code strips re 40. lifting selected groups of spring pile-ups when movably mounted on said drum, each code strip said lugs pass underneath »said pile-ups. having raised lugs for passing under and lifting11. In a signal privacy system having a' travel a selected spring pile-upV to close the pair of ingrecord medium and N reproducers spaced switch elements thereof. ‘ along said medium and including a distributor 5. The invention claimed in claim 2 in which 45 ofV P segments for dividing the signal into frag said-switches comprise relays each when operat ments in time, paths extending between each ed closing two circuits for selecting the'two ele-l reproducer and each segment, said paths being ments of a pair, and means for selectively oper NP in number, ating said relays. Y6. In a privacy system in which message cur 50 l rents are divided on a time basis into short frag ments and the fragments are transposed in time switches each controlling closure of a definite in irregular manner in recurrent cycles and in pair of said paths such that one signal fragment which the number of fragments in each cycle is is coded in converse relation to the other, and even number, the method of building up self 55 means to select and operate said switches in converse codes comprising conditioning in ad groups of v vance the fragment transposing means to trans pose the signal fragments in pairs such that the 2 time shift in one of the two fragments of the pair is the converse of that in the other and selecting to the group to build up a self-converse code. and operating enough of said transposing means 60 to provide the proper number of pairs of frag ments to fill up one cycle'. ` OSCAR MYERS.