US1633625A - Secrecy system - Google Patents

Description

JUN 28 1927" L. ESPENSCHIED SECRECY SYSTEM Original Filed March 5 1921 jvwantoz Patented June 28,

UNITED STATES l .PATENT vori-ica LLOYD nsrmrscnmn, or oumannw Yoan, .AssrGNoa 'ro Annalen: 'rnnnrnomi Aim 'rmemn connut, A conronarroN or Imaw You.

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muoltlon lied' Ilich 5, 1931, lclill lv This invention relates to transmission sys. tems and more particularly to a method of and means for providing secrecy in the transmission of messages ovei` such systems.

In general it is the object of the invention to rovide a Asystem of communication over which messages, such for example as telephonic-messages, ma be transmitted in such a manner that it w' l bepractically impossible for unauthorized persons who might have access to the medium through -or over which the messages are transmitted to obtain the 'information "contained therein. It is furthermorea feature 4of the arrangements of the invention that they are applicable .both to systems of communication employing metallic conductors as the medium of transmission and to radio systems. Other objects and features of the invention will appear more fully from the detailed description hereinafter given.

In the arrangements of this invention the message currents are rendered unintelligible at the sendin station by distortion and are transmitted ,in such unintelligible form to the receiving station. At the receiving station the incoming distorted message currents 'are given a compensating or -restoring distortion and thus Jrestored to intelligible form. The ori al distortion and restoring distortion ma accomplished by any suit- 'able electrica device lwhich has a nonlinear operating curve. Such a device, for urposes of illustration, mi ht lbe the we known vacuum tube ampl' er.. The distorting device at the sending station will be adjusted to operatemon a portion of its operating curve which has a non-linear characteristic, thereby distorting and rendering the messa e currents uninte ligible. The device at te receiving station will be adjusted to-operate on a ortion of its operating curve which is comp ementa to the rtion of the curve selected for t e o ration of the` distorting device at the sendmg station. In this manner the message currents may be restored a to' an intelligible form'at the receiving station'. The invention .may be more fully understood Ifrom th'e following description `when n. Maeva. aenewsa 0mm a, im.

read in connection with f the accompanyin i drawing, in the Figures 1, 2, 3 and 4 o which are illustrated the arrangements thereof. Figs. 1 and 2 are graphical illustrations of the operating characteristics of the distorting and redistorting devices respectively. In Fig. 3 are shown schematically the arrangements ofthe invention as applied to a one-way two wire line, while in Fig. 4 is illustrated how the arrangements might be embodied in a two-way circuit. Similar reference characters have been utilized to denote like parts in all of th/e figures of the drawing.

Asy has been pointed out the vacuunrtube amplifier is an electrical device having a nonlinear operating characteristic suitable for the arran ements of this invention. In Figs. 1 and 2 t ere is illustrated graphically the curve 7 which is the operating curve of the vacuum' tube, or more specifically the inputvo1tageoutputcurrent curve. It will be seen that this curve has non-linear characteristics near the lower and upper `parts of the curve and substantially linearl characteristics .near the central portion of the curve illustrated. Accordingly the distorting tube at the sendngstation will be adjusted to operate on a'non-linear portion of the curve such as the lower portion. The effect of this will be seen from a comparison of the wave forms 3 and 4. As the message current, especially in the case of telephone currents, is composed of a lurality of frequencies and is of a complex orm, the invention is illustrated b taking a wave form representing one of ese component frequencies and accordin l the wave forms 3 and 4 are of simp e to function. It will now be seen from the dotted line that the wave form 4. is composed i sulciently distorted to be rendered uninadjusted to function on a non-linear portionwhich are deemed desirable, it is under.

Kelli 'ble.

e tube at the receiving statlon will be of the operating` curve, such as the upper portion of the curve, which, is complementary to the portion of the curve on which the tube at the sending station functions. The result will then be as' illustrated by the wave forms and 6. `The wave form 5 shows the applied input volta e -rom the current of the wave form 4, which as hasbeen pointed out is in distorted and unintelligible form. The wave' form 6 will represent the output current which will result under these conditions due ,to the non-linear operatin characteristic at which the tube) is adjuste to function. It Will'be seen that the wave form 6 is composed of variations of equal amplitude and 1s similar to waveform 3. In other words the distortion, as shown b wave forms 4 and 5, will be removed and til restored to its original and intelligible form.

In Fig. 3 the arrangements of the invention are showgi i'n a one-way transmission line. In this arrangement the original message currents are transmitted over a section L of the transmission line to the. distorting device 1, by which they are rendered unintelligible. The message in unintelligible formation will then be transmitted to the receiving station over a channel, such" as L1, lt is pointed out that the channel L, might be a wire line or the messages might be transmitted to the receiving station by wireless methods and apparatus if desired. At the receiving station the messagesxin unintelligible formation would be transmitted through the restoring device 2 and thus restored to intelligible formation and thence transmitted over section L2 of the line to any suitable re-y ceiving apparatus. The distoter 1 vat the sendin station would operate in accordance with t e graphical representations of Fig.

1 and the restorer -2 would operate in ac cordance with the graphical representations of Fig. 2. It is pointed out that the devices 1 and 2 are not limited to vacuum tube amplifiers, but may be any suitable electrical devices .which have non-linear operating characteristics.

t In Fig. 4 the arrangements of the invention are shown in a twoway-ztransmission line. At each station in this type of line there would be provided the hybrid windings 9 and 10 and the balancin networks N, and N2, and the hybrid win such as 11 and 12, and the networks, lsuc as N, and N4. At each station there would be proe message current other than those illustrated. Accordingly,l while the arrangements have been illustrated,

as embodied in certain specific arrangements stood that they are capable of embodiment in many and widely varied forms without departing from the spirit of the invention as delined in the appended claims.

What is claimed is:

1. The method of providing secrec in a system of communication which consists in translating original message currents mto a current wave whose elements bear a non- It is linear `i'elation to the corresponding elements of the original message currents, transmitting Ithe -translated wave to a recelving station, and subjecting the -received wave' at said station to a non-linear translation complementary to the translation at the send'- ing station whereby the, message currents .will be restored to original formation.

l2. A transmission system including a sending station and a receiving) station, a transmitting channel at said sending station, a device in said transmitting channel having -a voltage-current operating curve portions of which are non-linear, said device being adjusted to operate on one of the non-linear portions of said curve to distort said message currentsin the same frequency range as the original message current'sfmeans or transmitting said message currents Ito said receiving station in'said distorted condition, a receiving channel at said receivin station, a rdevice insaid receiving channel aving a voltage-current operatinggcurve similar to the operating curve of said device at said vsending station, said device at said receiving station being adjusted to operate on a nonlinear portion of its curve which com-` plementary to the portion ofthe curve on'.

which said -device at s'aid sending station operates to remove the distortion from said received message currents torender them intelligible.

- 3. A transmission system including a sending station and a receiving stati n, a trans. mlttmg channel -at said sending station, a

vacuum bulb device in said transmitting channel having an in ut-vo'ltage output-current curve portions o .which have non-linear 1characteristics, saidv vacuum bulb bein --ad'- justed to `operate on one ofthe non-hnear portions of said curve to distort the message currents in the same frequency rangeI as the original message currents, means for transmitting said distorted message currents to said receiving station, a receiving channel at said receivmg station, a vacuum bulb denewness` i l B' vice in said receiving c-,hannel having an device atsaid sending station operates to input-voltage output-current curve similar remove the distortion from said received to the curve of said" device at said sending message currents to render them intelli ble. 10 station, said device at said receivingistation In testimony whereof, I havelsi ne my v being adjusted to operate one non-linear name tov this specification this 2n day of portlon of its curve which `is complementary Mai-cli, 1921. V-

to the portion` of the curve on which said LLOYD ESPENSCHED.

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