US1526335A - Secrecy transmission system - Google Patents

Description

Feb. 17, .1925.

E. v. GRIGGS SECRECY TRANSMISSION SYSTEM Filed Nov.

Patented Feb. 17, 1925.

ELMER. maniacs, OF EAST ORAivGE, NEW JERSEY, ASSIGNOR T wEsTEau ELECTRIC COMPANY, INCORPORATED, OF'NEW YORK, N. Y., A CORPORATION OF NEW YORK.

sEonEoY TRANSMISSION SYSTEM.

Application filed November 25, 1922. Serial No. 603,162. v v

To all whom it may concern: Be it known that I, ELMER V.

- citizen ofthe United States, residing at East The present invention relates to the trans; mission of currents or waves of different frequencies, or different ranges O'f freqnfeng vies for signaling or kindred purposes, and

.has particular reference to making such transmission secret.

It has been proposed to secure secrecy of transmission of a message wave, or similar wave, by resolving the wavev into essential component frequenc es and transmltting the difierent component frequencies over separate paths so that the components transmitted over any given path if intercepted would be insuflicient to enable the message to be understood. By recombining the component frequencies transmitted over all of the paths, however, the original message wave can bebuilt up and the message received; .A system employing thisprin'ciple is disclosed in U, S. Patent No. 1,395,378

to Wilson,-et 'al'., issued November 1, I921. In the present inventiona signal or other wave is resolved into component frequencies for separate transmission as in the previously suggested systems referred to, but it is a feature Of this invention. that the path Over which component frequencies of one. message-wave are transmittedv serves also to transmit components of other frequencies derived from another or other messa e wave or waves. This'n'ot only extends-t e per-,

missible. range --of component frequencies transmitted Overan' givenjpath thereby mcreasing the 1i1sefu ess of each path, bu t it also adds to the degree of secreoyfiofzthe "transmission since'th'e "current. components '45 which might be intercepted on any given path comprise portions of two ormore (lit-- ferent message waves and are still more complicatedand more confusing than the cOm-,

ponents in any one path that are derived from a single message. Injaccordance with this feature. of the invention, each path transmits a total range'of'frequencies which may be equal to or comparable with the frequencyrangeof anyone complete message,

We the range so transmitted, however, being Games, a-

composed of component frequencies from a plurality of message waves, the other components of 'the 'respectivemessage waves being transmitted over other respective p aths.

A"related feature of the invention is the distribution ofthe various component frequencies among the transmission paths so that in each path the frequency compo- :nents from the difi'erent messages build up to form a totalrangeo f suitable extent, that is, the various component bands of frequencies are dove-tailed together.

A further'featu're of'the invention is theprovision of noise or confusion currents to.

take the place of the message components when therel is. a cessation in the transmission of any given message. In the case of carrier wave transmission-systems these confusion currents may advantageously result from the interaction of'the carrier components themselves, due to arrangementsprovided by the invention, aswill be more fully described below.

Another feature of the invention relates to the provision. for transmitting call signals through the various channels .of the system.

The invention is: applicable either 'tO wire or wireless-transmission. Likewise the invention may be'usedwhere the message ourrents-are transmitted. at their own frequen-.

,cies, as in the caseiof a telephone line, or

where carrier waves are transmitted each accompanied by azfringe or band of frequencies' representing the message variations.

In' the caseof'speech transmission over a line, which may be taken as typical, the frequency components representing each speech message or conversation, are dividedb filters or other suitable means into relatively narrow bands of frequencies,' eac h band bevided. for purposes of the invention into,

say, three ranges of 200 to 800, 800 to 1400 and 1400' to 2000, respectively. If desired, a

larger orsmaller number than three bands may be' used. Assuming that three such sub ranges or bands arenised, whether com- 'ing insuflicient of itself to convey intelliprising the frequencies indicated above or Lines 1 11 A A 3 I A i Bands; r l I3 2 l3 1 i ll 3 C s 2 1 lVith this arrangement it is seen that each line transmits substantially the same range of frequencies as though normal speech were being transmitted over it.

.However, anyone obtaining access to a line would hear only sounds incapable of being understood. To receive an intelligible message it is necessary to select the proper band from each line and combine the bands so selected. The ditliculty presented to an outsider of doing this is increased as the number of lines in any vicinity is increased, the task of selecting out the proper ranges and n'iatching them together becoming very difiicult where several score of circuits of identical appearance are strung together as in a cable or on a pole line. 'However, the method used by the system for restoring the speech is simple in form and since the speech components are in no way mutilated the restored speech is of the same degree of quality as normally transmitted speech.

In the case of a'system employing carrier waves, either radiated or 'transn'iitted over wires, the application of the component bands to the various carriers may be exactly as indicated above for the lines I,-II, and III. the three carrier'channels taking the place of the three lines in the above table.

In the drawing, to which reference will now be made for a more detailed description of the invention, Fig. 1 is a diagram matic representation of one terminal of a three-channel system of preferred form, employing voice frequencyv transmission between stations; and Fig. 2 represents a terminal of 'a system employing carrier waves which may be radiated or transmitted over a line.

In Fig. 1, three lines L L and L which may be ordinary telephone lines, are used to convey three telephone messages between terminal telephone stations T T andiT and similar stations at the opposite ends of the lines, each line, however, carrying only a fragmentary part of any one telephone message as explained above. Thesetelephone stations may be of ordinary construction except for details to be noted hereinafter in connection with ringing and noise, current transmission, and are illustrated as local battery instruments although the invention is not limited to local battery circuits.

\Vhen the receiver 1 is raised, the speech waves from microphone 1 are impressed in the usual manner across conductors 2 and 3, across which are connected a group of filters F F and F which serve to se lect out from the speech waves component frequencies lying within definite frequency limits. For example, the filter F, may select and transmit through to the line L only those frequency components lying between the limits of 200 and 800 cycles. Similarly the filter may transmit to line L only frequencies between 800 and 1.400 cycles and filter I may transmit to line L only frequencies between 1400 and 2000 cycles. Any other arbitrary limits may be used for these filters and their construction and design are preferably in accordance with the principles set forth in U. S. Patent to Campbell No. 1,227,113, issued May 22, 1917. an identical group of filters 1. F and F is placed between the station T and the lines L L and L but these filters are so connected to the lines that the com ponent band of lowest frequencies, transmitted through F is impressed on line L the next higher component bandis transmitted by F to the line I, and the highest component band is transmitted through F to the line L A third group of filters,

identical with the other two groups, con- Y nects the station T to the lines, the filter F,

of thisstation being connected to line L 'the filter F to line L and the filter I to line L,. When speech is being transmitted from all three stations T T and 'I each of the lines L L and L carties a range of frequencies substantially the same as normal speech. However, if the limits of the filters F F and F are properly chosen, the currents on any one line represent only unintelligible sounds and the speech transmissionorer any line is to a very high degree secret.

Receiving and restoring the speech to intelligible form takes place in exactly the reverse order of the transmission. For example, currents received over the lines L L and L from three distant stations arranged similarly to the stations T T and T will contain such a number and arrangement of component bands that the. three component bands of one speech message,.

ponent bands of another speech message will be selected by the filters associated with station T and so on. The three component bands so received through the filters of station T are impressed across the conductors speech. Similarly; speech of another conuse, each line carries only two of the comversation is heard in the receiver of station T and so on.

Each line may serve to transmit ringing current in addition to the currents of speech frequency. For example, when the receiver 4 is on its hook, so that the contacts 5 are closed, ringing current may be sent out from the generator 6 through the branch 7 to the lineYL or may be received through branch 7 for actuating the ringer -8. The branch 7 preferably contains series inductance and shunt capacity as shown for preventing currents of speech frequency which may be present on line L due to a conversation taking place from station T or T fro bein shunted through the ringer 8 when station T is not in use and when, therefore, contacts 5 are closed. Also a condenser 9 may be employed on each line, of such capacitythat the portionof the line to the left of the point in the drawing at which the ringing currents are applied to, and derived from, the line, ofi'ers high attenuation to currents of ringing frequency, but readily. transmits currents of speech frequency.

With the arrangements described thus far, if any one station such as T is not in ponent bands of frequencies, and if two stations are idle and the other is being used, each line carries only one of the component bands. I It is conceivable that anyone exploring a group of lines could pick out.

the three lines that are used for one conversation, and also could identify the frequencies employed on each of the three lines for one conversation, if for any considerable length of time only one conversation, on

possibl only two conversations, were being transmitted. In order to forestall such possibility, it is preferable to provide a source of noise currents of speech frequency range and to substitute these noise currents for speech when the speech currents are withdrawn. Such-a source is indicated on the drawing, and .it may, in practice, advantageously com rise a phonographic apparatus or the 1 ke. Currents from this source' pass to the; transformers 10 of the respective stations. When the re-,

ceiver 4 of any station is replaced on theswitchhook after completing a conversation, the contacts 11 are closed andthe noisecurrentsof s ech frequency are impressed across con uctors'2 and 3 and are practice. 'hybrid coil lead s to the input of a moduplace of the essary to associate the lines L L and L of Fig. 1 with the terminals of three re-.-

spective carrier wave channels such as are shown in Fig. 2, and for the purposesof understanding the application of the invention to carrier wave transmission, it will be assumed that the line L of Fig. 1 is con-' nected to the line L, of Fig. 2, and that the lines L and L of Fig 1 are similarly connected respectively to the line terminals 35 L and L, of Fig. 2. The carrier channels indicated at CH CH and CH, of Fig. 2 serve in thewell-known manner to translate the speech frequency waves received from the station of Fig. 1 into "modulations of high frequency carrier waves to be transmitted to-the distant station, and likewise serve to translate received modulated carrier waves into waves of the speech range. for transmission back over the lines L L etc. to the station of Fig. 1. The channels CH etc., of Fig. 2, are specifically shown. as being associated with the terminal of the multiplex carrier line ML, but this may equally well be the terminal of a radio system, in which case the carrier waves' would be radiated to the distant station.v At the distant station, it will be understood, carrier wave terminal apparatus will-be provided for cooperating with that shown in 10 Fig 2, and the character and arrangement of this terminal apparatus may be identi- Y cal with that shown in Fig. 2. The car-' rier channels at the distant station will be extended by lines to telephone terminal ep- 1 paratus which may be identical with that showninFig.1. The carrier channels of Fig. 2 may be identical with each other, except for the carrier frequencies which the. respective chan nels employ. The specific arrangement of the channels is indicated'in'the showing of .the channel (3H,. The low' frequency terminal line L, of this channel is provided with a conjugate'repeating coil, or hybrid coil H and a balancing network N -in accordance with usual telephone repeater The transmitting branch of this lator M which is supplied by a sustained high frequency wave from generator O of the carrier frequency employed by the channel CH in transmitting. The output side of the modulator is shown connected thru an amplifier A to the band filter BF,-

which is designed to transmit the modulated wave to the line BIL. This carrier line ML is shown provided with a balancing network MN and a hybrid coil H tor'enahling carrier waves to be impressed on the line ML and received from it without interference. Channel CH, is connected with the receiving branch of the hybrid coil H by means of the band filter BF H the detector 1),. the amplifier .A and a low frequency filter LF. The hand filter BF, is designed to have a. transmission range for only the frequencies employed by the channel CH, in receiving and the filter LF is designed to transmit frequencies in the voice range. The filter Ll preteraliily suppresses both the components of frequencies lower than the essential speech frequencies and components of frequencies higher than the essential speech frequencies, its trans mission range for example, being from 200 to 2000 cycles.

The general arrangement of the channel CH and ihe operation of the carrier apparatns is substantially thesame as that described in the paper entitled Carrier Current 'llelephony and Telegraphy by E. H. Colpitts and 0. l3. Blackwell, published'in the Journal of the American Institute of Electrical Engineers, beginning I April, 1921. The specific construction and arrangement oi the individual parts of the channel CH, may be understood from this publication. F01" further reference, the oscillator 0 may be of the type shown in the U. S. patent to Hartley 1,35G,T63, October 26, 1920. The filters may each be constructed in accordance with the principles disclosed in U. S. patent to Campbell, 1,227,113. above referred to, and the amplifier, modulator and detector may be of the well-known vacuum tube type such as are shown in the (lolpitts and Blackwell publication. 7

The channel CH may have an arrangement precisely similar to the channel CH except that the oscillator O. of this channel generates a carrier wave of a frequency different from that supplied by the oscillater 0 and the band filters BF, and BF are designed to transmit selectively and exclusively the modulated waves employed by this channel for sending and receiving. Similarly the oscillator 0., and the band filters BF, and BF are designed for the frequencies employed exclusively by the channel CH the arrangement of the channel being otherwise the same as described in the case of channel CH,

The waves 01 the speech range representing components derived from dilterent conversations and transmitted over the line L from the station of Fig. 1, traverse the line L, and pass into the input circuit of the modulator M where they serve to modulate the carrier wave supplied from the generator 0 and the resulting modulated wave is selectively transmitted to the line ML. In similar manner waves received over the lines L and L, modulate the respective carrier waves supplied from the generators O and and the resulting modulated waves are transmitted to the line ML. The manner in which these modulated waves are received and retranslatcd at the distant station will be clear from considering the reception and translation of waves received over the line ML at the station shown in Fig. 2. The receiving filters 131 BF and BE, serve to separate the incoming transmissions to their respective channels CH Cll and CH The wave received by the channel CH is detected at D and after amplification, is selectively passed through the voice filter LF to the line L, and thence over the line L to the station of Fig. 1. The waves received by the other channels are similarly translated and the speech components are transmitted over the lines L. and L, to the station of Fig. 1.

Ringing current transmitted over the line L passes into the, circuit of the modulator M and there modulates the carrier wave in the same manner as described in thecase of speech waves. These ringing currents are assumed to have a frequency below the speech range and may, for example, be out the order of 100 cycles, or lower, if desired. Accordingly these ringing currents received over the line L, are suppressed in the filter LF and are prevented from producing disturbances in the receiving side of channel (1H,. A wave received over the line ML by the channel CH and modulated by ringing currents is detected at D and after amplification at A, causes the energization of relay 15. The ringing currents so received are prevented from passing to the hybrid coil H by the filter LF, this filter, as described, being designed to suppress currents of the "frequency employed for ringing. Relay 15 in pulling up its armaturcs in response to the receipt of the detected ringing current closes a circuit or the ringing relay 1G and also closes a circuit 17 in shunt of the input circuit of the modulator M,. Ringing relay 16 in pulling up its armatures applies ringing current from the source indicated to the line L,', from which it passes over the line L and to the apparatus shown in Fig. 1. Closure of the circuit 17 as described short-circuits any disturbing currents arising from the ployed, and especially the'case of radio signaling, the carrier waves themselves 'afford a convenient method offproducing noise or interference "currents, whether speech is being transmitted on all three channels or not. The filters in the various receiving and transmitting sides of the channelsare preferably designed to transsuppress thetransmission of the other sidemit the carrier frequency and one side band of the respective modulated wave, but to.

band.

According to this invention the filters v will be so designed that-the upper side band" and the carrier will be transmtted in the case of one channel, and inthe case of the' channel employing the next lower carrier frequency the carrier-and lower side band will be transmitted. This scheme may be repeated for each pair offcarrier waves; By

so relating the frequencies of the neighboring channels, it is possible to set the frequencies of two carriers so close to each other that their separation is .of the order of the extreme limits of'a speech side band or less; For example, a carrier wave of 8000' cycle's'may be transmitted with its upper side band, representing a total range of' 8000 to"10,000 cycles or thereabout. The next lower. carrierfrequency maybe 7000 and-its lower side-band would extenddown ward'to, sa 5000 cycles. These two ranges can easily e' separated from each other-.by, suitable filters. However, if an outsider should attempt to receive the secret message by impressing all of the received frequen cies on a detecting circuit, on the theory that it might .be possible to detect portions of a conversation that happen tocontinue the detected, speech is greater, the greater during a pause in each of the other conversations, he would be defeated in this since the two carriers would interact to give a detectednote of an audible frequency, 1000 cycles in the example, given, which would The carrier be-superposed on-the signal. components are preferably made of large amplitude compared with the side bands, and as a result the detected beat 'betweentwocarriers will be louder than any signal .component, and may easily be-made so much louder as to overwhelmthe, signal. This large amplitude of the carrier offers'no disadva11tage to the secret reception of the messages since the carriers are'scparatelydetected, "It is rather an advantage since,

other things being*equal,- theclearness of the amplitude of the carrier component.

'Whatis-claimed is: Q I

In a'signaling system, a plurality of sources of-signaling waves representing different messages to be transmitted, a plurality of transmission pathsfor effecting the simultaneous transmission of said messages,

and means-to transmit a correspondingly.

difierent' portion of each message wave simultaneously over each of said paths.

2. In a signaling system, a plurality of sources of signaling waves representing different messages to "be transmitted, a plurality .of transmission paths for effecting the simultaneous transmlssion of said messages,

means te-distinguish a corresponding plurality" of characteristically different portions of each message wave, and means to transmit simultaneouslyover each of said paths acharacteristically different portion of each :ofsaid, message waves.

In a signaling system, a plurality of sources of 7 transmission paths for enablingthe simultaneous transmission of-all of said -mes- Sages,"means*to resolve each message wave message "waves, a plurality of into components differing from one another respectively infrequency, and means to transm t over each of said paths simultaneouslya portion of eachof said message waves, each portion transmitted over a given path having a different frequency.

.4. In a telephone system, sources of waves representing different telephone messages, a plurality of paths forenabling the simultaneous transmission of said messages, means'itoresolve each message into a plural- .ity of component frequency bands, and meansto' transmit over each of said paths a' plurality of said bands derived from a plurality of different messages. a

5. In a telephone system, sources of waves each of said pathsa plurality of said bands derived each from a different message.

6. In a telephone system, a plurality of transmission'paths, means to transmit waves of 'a-rangeof frequencies over each path, the waves transmitted over. each path being incapable of reproducing understandable speech, means to resolve the waves transmitted over each path into aplurality of comonent frequency bands, and means to comeach band derived from the wave transmitted over a transmission path with a band derived from the wave transmitted over anable speech. i

other of said :paths to produce understand-.-

I telephone system, a' plurality of telephone 'stations'fa corresponding. plurality of transmission =eircuits connected to said stationswave .fi'lters inter osed between each station and "each of t e several circuits, the filters cdnnected-to each station being. ,proportioned to*'transmit v-a different frequency from said, station and each or.

thedifferentlcii'cuits. I

8. In a telephone system having 'a plurality of telephone stations, acorresponding plurality of transmission circuits associated with said stations, means to transmit over a said transmission circuit currents of fre quencies of the range of essential speech frequencies, and means to derive'certain of the frequencies composing the transmitted range from one of said stations and certain other of the transmitted frequencies from another of said stations.

9. A telephone system having a plurality of telephone stations, a plurality of transmission circuits associated with said stations, and means to transmit over each one of said lines simultaneously currents derived from each of said stations, the currents on each line derived from the respective stations being of respectively different frequency.

10. In a telephone system, a plurality of telephone stations each for translating sound waves into current variations, aplurality of wave filters associated with'e'ach station for selecting from the current variations com ponents of different ranges of frequency, plurality of transmission circuits associated with said stations, each circuit being connected to one of said stations through one of said filters, and to another station through a filter having a different transmission frequency range.

11. In a secret telephone system, a plu- 'rality of telephone stations, wave filters associated with each station for deriving from the speech waves produced in the respective station a plurality of different bands of component frequencies, a plurality of trans mission lines, means toconnect one of said stations with the first of said lines through a filter transmitting only the lowermost band of component speech frequencies from that station, and with the second of said lines through a filter transmitting only the next higher of the bands of component frequencies from that station, and so on, and means to connect another of said stations with the second of said lines through a filter transmitting only the lowermost band of component frequencies and with the first of said lines through a filter transmitting only the next higher of said bandspf component frequencies, and 'so on.

12. In a secret telephone system, a plurality of telephone stations each having means to produce speech currents and to separate the currents into components lying in definite frequency bands, a plurality of transmission lines for transmitting the currents from said stations, and connections for distributing the bands of components from each station to a plurality of said lines.

13. In a secret telephone system, a plurality of telephone stations, means to produce separate speech waves in each station, transmission circuits associated with said stations, and means to effect secret transmission of said speech waves over said lines comprising means to transmit diiferent portions-of the speech waves from'each station over the several lines.

14. In a secret telephone system, a plurality ,of telephone-stations, means to pro duce separate speech waves in each station, lines associated with said stations, means to transmit over each line a portion of the speech waves f'rom'one of said stations, and means to render unrecognizable the particular portion of the waves on any line derived from any station comprising means to superpose thereon a portion of the waves from another of said stations.

15. In a secret telephone system, a plurality of telephone stations, a plurality of transmission lines, means to produce speech waves in each of said stations, means to mingle the waves from all of said Stations in each of said lines to render the individual speech waves unrecognizable, and means to derive a plurality of speech messages from the mingled Waves on said lines.

16. In a secret telephone system, a plurality of telephone stations, a plurality of transmission lines associated therewith, means to transmit telephone currents from each station over a respective line, means to utilize on each line speech currents from a respectively different telephone station to mask the wave transmitted fromthe aforementioned station associated with the respective line, a source o'f'noise currents, and means operative upon the establishment of the non-talking condition in a station for transmitting noise currents from said station for masking speech currents from other stations.

17. Ina telephone system, telephone stations including sources of speech waves, sources of noise waves associated therewith, a plurality of paths for enabling the simultaneous transmission of waves from said stations,-means.to resolve the waves from each station into a plurality of component frequency bands, means to transmit over each of said paths a plurality of said bands derived from a plurality of said stations, and means controlled in each station to transmit from said station speech waves and noise waves alternately.

18. In a secret telephone system, a telephone station, a line for transmitting speech currents from said station, means to confuse the speech currents so transmitted com,- prising a second station and means to superpose speech currents from said second station upon the currents transmitted on said line, a source of noise currents of essential speech frequencies associated with said second station and means to substitute said noise cur nuts for the speech currents from said second station.

'19. In a secret telephone system, a .plurality of carrier wave transmission channels, separate sources of speech waves, and means for through each of said channels acorrespondingly' different portion of the waves from each of said sources.

20. In a secret telephone system, a plurality of two-Way carrier transmission channels, voice frequency terminals for said channels, said terminals of the'respective channels being associated with the respeotive transmission lines of the system defined in claim 9.

21. In a secret telephone system, a plurality of two-way carrier transmission channels, voice frequency terminals for said channels, aid terminals of the respective channels being associated with the respective transmission lines of the system defined in claim 11.

22. In a secret telephone system, a plurality of two-way carrier transmission channels, voice frequency terminals for said channels, said terminals of the respective channels being associated with the respective transmission lines of the system defined in claim 15.

23. In a carrier signaling system for transsimultaneously transmitting.

mitting a signal comprised of a range of frequencies, means for transmitting a pair of carrier waves differing in frequency suf- 'ficiently to enable their separation by wave filters, the frequency difierence between said carriers being less than the extreme range of frequencies comprised by said signal, means to modulate each of said carrier waves by a different portion of the frequency range of said signal to be transmitted, and means to confine the modulation components in the transmitted waves to the upper side band of the wave of the higher frequency and to the lower side band of the Wave of the'lower frequency. I

24. In a carrier signaling system, sources of signaling waves to be-transmitted, means to produce two modulated carrier waves of different frequency, each modulated by one my name this 23rd day of November, A. D.,

ELMER- V. GRIGGS.

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