Sept. 7, 1926. 1,598,673 O. B. BLACKWELL ET AL SECRECY COMMUNICATION SYSTEM Filed Dec. 18, 1920

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(2AA%aeaeAA 8 eletoz/vie Patented Sept. 7, 1926. 1,598,673 UNITED STATES PATENT office. OTTO B. BLACKWELL, OF GARDEN CITY, NEW YORK; DE Loss K. MARTIN, or oRANGE, NEW JERSEY; AND GILBERT S. VERNAM, OF BROOKLYN, NEw YoRK, AssGNORs TO AMERICAN TELEPHONE AND TELEGRAPH. COMPANY, A CoRFoRATION of NEW YORK, sECREGY coMMUNICATIoN sYSTEM. Application filed December 18, 1920. Serial No. 431,721. This invention relates to a signaling sys pear more fully from the detailed descrip 50 tem wherein signals are transmitted by the tion hereinafter given. agency of a high frequency wave modu The arrangements of the invention are ill lated in accordance with said signals, and lustrated in the accompanying drawing, in more particularly to a signalling system em the figure of which is shown a sendingsta ploying a plurality of high frequency tion of a system embodying the invention. 35 waves. It is the object of the invention to In the arrangements of the drawing are rovide a system of communication where shown four low frequency channels 1, 2, 3 y secret communications between stations and 4 from which the low frequency sig 10 may be had to the end that stations, other nals, such as four telephone messages, may than those designed to receive, may not re be transmitted through modulating appara 60 ceive complete, intelligible signals. tus out over a transmission line L. The Heretofore in certain types of signaling modulating apparatus is shown schemati systems, in which a high frequency wave is cally and includes the modulators M., M., 15 utilized as the agency for transmitting the Me and Ma, with which are associated the signals, he signals have been transmitted high frequency sources A, B, C, and D, 65 by electromagnetic waves of a definite high which are of suitable different frequencies. frequency or wave length and any station These modulators may be of the duplex vac tuned to said wave length might be capable uum bulb type illustrated in the U. S. 20 of receiving said signals. In the present. Patent #1343,307, dated June 15, 1920, in invention secrecy is obtained by the trans the name of John R. Carson, although other 70 mission of signals on a plurality of waves types of modulators may be used. These of different frequencies, successive portions modulating devices are associated with the of a message being transmitted on waves of low frequency channels 1, 2, 3, and 4, by 25 different frequencies whereby a station means of the hybrid coils 17, 18, 19 and 20, tuned to one of said waves receives only a the conductors 5, 6, 7 and 8, and over the 5 partial and therefore unintelligible disclo contacts of a plurality of series of relays, sure of the communication. The arrange such as the relays 13, 14, 15 and 16, and the ments of this invention present the addi relays 9, 10, 11 and 12. Associated with 30 tional secrecy feature that the shifting of the above mentioned hybrid coils are the the low frequency signals or portions of the balancing networks N, N N and N. In 80 message, to the various high frequency cluded in output circuits of the modulators waves or channels is not accomplished in a are the band filters F, F, F, and F, which cyclic order but rather in a random and va readily transmit the band of high frequen . 35 riable manner. To this effect printing tele cies of the order of the particular high fre graph apparatus and key tapes are utilized quency source associated with each modula 85 to shift the low frequency signals in a va tor but which attenuate and practically ex riable manner to the high frequency chan tinguish frequencies outside of said band. nels, the shifting being controlled in ac These filters may be of the type illustrated 40 cordance with the perforations and setting in the U. S. Patents No. 1227,113 and No. of the key tape utilized. With this ar 1,227,114 to G. A. Campbell. The output O rangement the messages would be unintel circuits of the modulators are associated ligible to unauthorized persons, who might with the line L through the hybrid coil 21, . have access to the medium through or Over the conductors 22 and the high pass filter 45 which the messages are transmitted, unless F. The filter F, readily allows the trans such persons should be provided with the mission of the high frequency carrier cur 95 key tapes utilized at the sending station in rents utilized but attenuates and extin addition to other information. * Other ob guishes the low frequency currents trans jects and features of the invention will ap mitted over the line L, such as of the nor 1598,078 mal speechor telegraphic frequencies. In order that the messages coming in over line transmitter to be pulled down and will step I may be received over the lines 1,2,3 and brushthe {{???? passes of keyof segment tape ahead. 32 the Whenmagnet the 35 4, there is associated with the high fre will be released and the contacts of the trans quency sources A, B, C and D, the demodu mitter will be pressed against the key tape. () lating devices IDM, DM, DM, and DM, If there are no holes in the perforated key which may be of the duplex vacuum bulb tape, the contacts 39 and 40 will remain open type illustrated in the U. S. Patent No. as shown Under such conditions none of 1343,308, dated June 15, 1920, to J. R. Car the relays 9, 10, 11 and 12, or the relays 18, . . . 10 son. Included in the input circuits of the 14, 15 and 16, will be operated. Under these 5 demodulators are the band filters F. F. F. conditions, line 1 will be connected to the and F, adapted to readily transmit bands modulator MA over the back contacts of of frequencies respectively such as those relays 9 and 18, over conductors 5, and from the sources D, C, B and A and to at through hybrid coil 17. The line 2 will be ls tenuate and extinguish frequencies outside connected to the modulator Ma over the 80 of said bands. The output circuits of the back contacts of relays 10 and 14, conductors demodulators are associated with the lines 6 and the hybrid coil 18. Line 3 will be con 1, 2, 3 and 4, by means of the hybrid wind nected to the modulator Mc over the back ings 17, 18, 19 and 20, conductors 5, 6, 7 and contacts of relays 11 and 15, conductors 7 20 8, and over the contacts of the series of re and the hybrid coil 19. Iine 4 will be con 86 lays, such as relays, 13, 14,15 and 16, and nected to the modulator M over the back relnys 9, 10, 11, and 12. The operation of contacts of relays 12 and 16, conductors 8 the series of relays, such as relays 9, 10, 11 and the hybrid coil 20. It is pointed out that and 12, and relays 13, 14, 15 and 16, is con under such conditions the low frequency sig 25 trolled by the printing telegraph transmit ter 36, the contacts 39 and 40 of which are nals from the lines 1, 2, 3, and 4 will be im controlled by a perforated key tape, not ressed on different high frequency waves shown. Associated with the tape transmit thenfrom bethe transmitted sources A, outB, overC, and the D,line and L inwill a ter is the distributor 29 for timing the se well known manner. When the brush of the 30 uence of operation of the arrangements. distributor crosses segment 33, a circuit will le distributor 29 is associated with a re be closed over conductor 37 and through the lay, 26 and the pole changing apparatus 25, winding of relay 88, to battery, and ground, which in turn is associated with the usual thereby energizing relay 38. However this type of composite set 23 associated with the will have no effect at this time as neither of line L. Associated with composite set 23 is the low pass filter F, which readily allows the contacts 39 and 40 were operated and the transmission of the low frequency cur 14,none 15, of andthe relays16 were 9, 10,previously 11, and 12operated. and 13, rents, such as the telegraph currents and the When the brush of the distributo again currents from the pole changing apparatus 40 crosses segment 31, the relay 26 and the pole 25, but which shuts out the high frequency changing device 25 will operate as previously 105 carrier currents. pointed out to transmit an impulse to the dis Operation of the sending arrangements of tributor at the receiving station. When the the invention is as follows: brush now crosses segment 32, the magnet 35 The perforated key tape will be inserted will again be operated and will pull down in the tape transmitter 36 and the key K the contacts and will step the key tape ahead. O thrown. The throwing of key K will close a For purposes of illustration let us assume circuit for the relay 30. This will release that the perforations in the tape are now so the latch and allow the brush of the distrib arranged that contact 39 may be closed and 50 utor to start rotating. When the brush of contact 40 may remain open when the brush the distributor crosses segment 31, the foll now leaves segment 32. and the magnet 35 is 5 lowing circuit will be closed; from ground, again released. When the brush now crosses brush of distributor, segment 31, conductor ??? 38, the relay 38 will be operated. 28, winding of relay 26, to battery and The operation of relay 38 and the contact 39 ground. This will operate relay 26, which will close the following circuit; from ground controls the pole changer 25, whereby im and battery, through the windings in series 20 pulses of either polarity may be transmitted of the relays 16, 15, 14, 13, and 41, conductor. over the line L to the distant station to-con trol a distributor thereat, to time the sequence 43, contact 39, conductor 50, armature and of operation of the receiving arrangements as contact of relay 38, to ground. The closing 00 of this circuit will operate the relays 16, 15 will be pointed out later. When the brush 14, 13, and 41. When the brush passes offo 25 of the distributor crosses segment 32, a cir segment 33, the relay 38 will be released. How cuit will be closed over conductor 34, mag ever, the re? ays 13,1415, and 16, and the relay. net 35, to battery and ground, thereby oper 41 will remain locked up as a locking circuit (55 ating magnet 35. The operation of magnet will be closed over the contact and armature 35 will allow the contacts 39 and 40 of the of relay 41, conductor 51, break contact of 13

f 1,598,678 set 28 as shown. The polar relay 76 is con trolled by the impulses sent over the line.L. many and widely varied forms without de from a pole changer, similar to 25, at the dis Äefined infrom the appendedthe spirit claims,of the invention as tant station, which, as has been pointed out, What is claimed is: is controlled by the distributor thereat. It , 1. A transmission system in which a plu 0 is pointed out that the relay 76 of the re rality of high frequency channels are pro ceiving system is connected to the upper side vided as the agency for transmitting low of line I. The pole changer at the distant frequency messages over said system, an station which controls relay 76 would also be equal number of low frequency signaling O connected to the side of line L, The lines, each of said low frequency lines being 75 pole changer 25 is herein illustrated as con associated with one of said high frequency nected to the lower side of line L, and it channels, and means for shifting in a ran is understood that the receiving relay at the dom and variable manner each of said low distant station would also be connected to frequency lines from the high frequency the lower side of line L. With this arrange channel associated therewith to a high fre 80 ment there will be no interference between quency channel previously associated with the pole changer and receiving relay at the another of said low frequency lines. same station. The distributor 29' will be 2. A transmission system in which a plu used to control a tape transmitter 86, the rality of high frequency channels are pro contacts 39' and 40' of which will be wired vided as the agency for transmitting low 86 similar to contacts 39 and 40 to control the. frequency messages over said system, a plu relays, 9, 10, 11 and 12 and 18, 14, 15 and rality of low frequency signaling lines, each 16. Segment 33' of distributor 29' will, in of said low frequency lines being associated a manner similar to segment 33 of distribu with one of said high frequency channels, a tor 29, be utilized to control relay 38. The 90 key tape utilized at the receiving station will key tape, and means controlled by said key be similar to the one used at the sending tape for shifting each of said low frequency station and will be inserted in the transmit {??ES, to other of said high frequency chan ter 36' in the same position with respect to 3. A transmission system over which a 3) its perforations as the key tape at the send lurality of low message frequencies may 95 ing station. Accordingly when the perfo e simultaneously transmitted on different rations in the key tape at the distant sending carrier frequencies, a printing telegraph station so control the arrangements that the transmitter, and means controlled thereby low frequency channels similar to 1, 2, 3 for changing the relations between said low and 4 are superimposed on the high fre message frequencies and said carrier fre quency waves A, B, C and Dres ectively, quencies over which said low message fre as has been pointed out, the distributor 29 uencies were previously transmitted so and transmitter 36' together with the key that said low message frequencies will be tape thereat will control the receiving ar transmitted over different ones of said car () rangements so, that the low frequency re rier frequencies than previously. 06 ceiving channels 1, 2, 3 and 4, will be simul 4. A sending station, a plurality of mod taneously connected with the demodulators ulating devices thereat with which are asso associated with the high frequency waves A, ciated different high frequency carrier cur B, C and D. When the low frequency chan rents, a plurality of low frequency trans nels at the transmitting station are now mitting circuits associated with said modu 10 shifted to other of the ?? frequency waves lating devices, a printing telegraph trans a similar shifting will take place in the con mitter, and means controlled thereby for nection of the low frequency receiving chan changing the relation of said low frequency SO nels with the demodulating arrangements at transmitting circuits with said modulating the receiving station. devices. 15 It is pointed out furthermore that while 5. A sending station including a plural the arrangements of the invention have been ity of modulating devices with which are specifically shown as associated with a trans associated different high frequency carrier mission line, such as IL, that the messages currents, a plurality of low frequency trans might equally well be transmitted by wire mitting circuits associated with said modu 20 less apparatus. In such event it would be lating devices, a printing telegraph trans desirable to substitute for the pole chang mitter, means controlled thereby for chang ? device 25, other apparatus and a separate ing the relation of said low frequency trans 30 radio frequency for maintaining synchro mitting circuits with said modulating de nous operation between the distributors at vices, and a receiving station including a 12S the ?????? and receiving stations. plurality of demodulating devices with While the arrangements have been dis which are associated different high fre closed in certain P???? arrangements which quency currents of the same frequencies as 66 have been deemed desirable it is understood that they are capable of embodiment in asaid plurality carrier ofcurrents low frequency at said sending receiving station, cir 180 1,598,678 w cuits associated with said demodulating de ship between said low frequency transmit vices, a printing telegraph transmitter op ting circuits and said modulating devices. 10 erating synchronously with the transmitter In testimony whereof, we have signed our at said sending station, and means con names to this specification December 1, 1920, trolled thereby for maintaining a change in December 16, 1920, December 1, 1920. the relationship between said low frequency OTTO B. BLACKWELL. receiving circuits and said demodulating DE LOSS K. MARTN. devices similar to the changes in relation. GILBERT S. VERNAM.