US1632099A - Secret signaling - Google Patents

Description

June 14, 1927.

J. c. SCHELLENG SECRET SIGNALING- Filed Aug. 12. 1925 T o-aomw b MAW);

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Patented Jane 14, 1927.

UNITED STATES PATENT OFFICE.

JOHN C. SGEELLENG, OF MILLBUB NEW JERSEY, ASSIGNOR TO WESTERN ELECTRIC commnv, nzconrona'rnn, on NEW YORK, n. Y., A coaronarron or raw roan. sncanr srennme.

-App1ication filed August 12, 1925. Serial No. 49,785.

This invention relates to signaling systems and particularly to arrangements for providing secrecy in the transmission of messages over such systems.

An object of the invention is to-transmit signals which shall be intelligible only at a properly equipped receiving station.

A further object is to secure secrecy in message transmission without having to add any other frequency components or utilizing a wider frequency range than that comprised in the original message. a

The effectiveness of several promising systems of secret message transmission which have been proposed heretofore has been limited by the fact that it is exceedingly difficult in practice to provide a scheme of mutilation which will enable the speech to be restored and understood at the receiving station but to be practically unintelligible for unauthorized listeners. This difficulty in many of such systems seems to be due in part to the fact that the voice frequencies within certain small ranges are transmitted in their original relationships with respect to each other, and a certam amount of intelligibility is associated with even a small range of frequencies. Therefore, in such cases it is possible for an unauthorized listener, by using heterodyne reception, to understand a few wordsof the transmitted messages. Moreover, imperfecw tions in the transmitting apparatus or in its adjustment may permit a small amount of the original speech to be transmitted without change. I

In accordance with the present invention a message band such as speech is transmitted with secrecy within substantially the same 40' fre uency limits as the original message ban This is accomplished by dividing the message waves arbitrarily into sets of fragments on a time basis, reducing the frequency of each component of the successive ra ents by a factor equal to the number of ragments in a set raising the frequency of each component of at least one fragment in each set, superposing the various fragments of a set, the components of which are so changed in frequency, and transmitted to ether the superposed fragments within su stantially the frequency limits of the original message band.

' In'the particular embodiment ofthe in,-

vention to be described, a message wave is divided into successive time intervals which are sent in rotation over different channels to a mam transmission path. A s cial automatic devlce, such as a telegrap h one, inserted 1n each of these channels, first records the speech intervals and then re roduces them at substantiall half s e so as to destroy their intelligibility. he frequencles 1n one channel are then raised by modulatlon so that the absolute frequency range of the frequencies in the two channels i do not overlap. The two channels converge and the two bands of frequencies are transm tted together over a transmission path by wire or radio, the total fre uency range of the transmitted fragments ing the same as the range of the original speech.

At a receiving station means are provided for separating the two frequency bands and for dlverting them into separate receiving channels. The raised frequencies in the freguency band in one channel are then reneed to frequency by demodulation by the amount they were raised at the transmitting station. Devices similar to those at the transmitting station are utilized in each channel at the receiving station first to record and then to reproduce the messa e fragments, these devices being'arranged in this case, however, so that the fragments are reproduced at twice the speed of recording. The apparatus at the receiving station is synchronized with that of the transmitting station by suitable means so that the reproduced fragments in the two channels at the receiving station, which fragments now have their original frequency values, may be supplied to a suitable receiving circuit in their proper successive order so as to be intelligible.

The particular advantages and features of the invention are brought out more clearly in the following detailed description when read in connection with the accompanying drawing, in which Fig. 1 is a dia- 100 grammat-ic illustration of one embodiment of the invention applied to a communication system and Fig. 2 is an illustration in section of one form of contacting device which may be used in the system of Fig. 1 10s to divide the message wave into fragments .on a time basis.

sion line ML is shown. The circuit at the transmission terminal comprises a transmitter circuit T, adapted to be connected by means of the switch S with line ML through either one of two channels 1 or 2. The operation of switch S is controlled by clectromagnet 3 which is energized by battcry 4. For the purpose of connecting transmitter circuit T in rotation to channels 1 and 2 for desired intervals of time, the battery circuit for electromagnet 3 is alternately made and broken by means of the cont-actor device 5, which is driven at a desired speed by the synchronous motor SM in the manner which will be described later.

The contactor device 5 may be in theform of a commutator comprising, as shown in detail in the sectional view in Fig. 2, a metal portion 26 and an insulation portion 27, so arranged that the brushes 28 make contact with the metal portion 26 for half a revolution of the commutator and with the insulation portion 27 for the remaining half revolution of the commutator.

An automatic device TGr which maybe of any form which is adapted for recording speech intervals and reproducing them at substantially half the speed of recording is inserted in channel 1. The device TGr illustrated comprises a recording electromagnct 7, a thin steel telegraphone disc 8, and a reproducing electromagnet 9. A similar device TG comprising the recording electromagnet 10, thetelegraphone disc 11 and the reproducing electromagnet 12, is inserted in channel 2. The discs 8 and 11 are mounted on a shaft 13 which is rotated at a desired speed by the motor SM.

The recording electromagnets 7 and 10 are stationary and are mounted in close proximity to the outer edge of discs 8 and 11, respectively. A sleeve spindle 14 having a sliding fit on shaft 13 is adapted, by means of a train of gears 15, 16,17 and 18 of properly selected diameters, to be driven by the motor SM in the same direction as disc 8 but at substantially half its speed. The reproducing electromagnet 9 of device TGr is mounted near the outer edge of disc 8 on crank arm 19, which is atlixed to gear 15. The gear 15 is mounted on the sleeve spindle 14, and, therefore the electromagnet 9 will rotate in the same direction as disc 8 but at half its speed. The commutator of contractor device 5 controlling the operation of switch S, is mounted on the sleeve spindle 14 so that it rotates also at a speed which is substantially half that of the discs 8 and 11. The reproducing magnet 12 of the device TGr in channel 2 is mounted in close proximity to the outer edge of disc 11 on a crank arm 20 which is affixed to the gear 21. The gear 21 is freely mounted on shaft 13 and by means of the train of gears comprising gears 'prime mark after the characters.

22, 17 and 18, is arranged to be driven by motor SM in thesame direction as disc 11 and at half its speed. The reproducing electromagnet 12 will, therefore, be rotated in the same direction as the disc 11 but at half its speed.

The switch S. the operation of which is controlled by the same electromagnet 3 which controls the operation of switch S 'is adapted to connect erasing battery 23 alternately to electromagnets 7 and 10. The contacts of switches S and S are so arranged that the erasinsr battery 23 will always be connected to the particular channel to which transmitter circuit T is not con: nected.

The output leads of the revolving electro magnet 9 in channel 1 are arranged to be connected to line ML at all times by suitable means such as the commutator device 24,

comprising a commutator ring 29 rotating with but insulated from sleeve-spindle 14 and stationary brushes 30 making contact with commutator ring 29. The output of reproducing electromagnet 12 in channel 2, however is connected, through a commutator device 25 similar to device 24 in channel 1, to the input circuit of a modulator M. A source of oscillations O is also connected to the input circuit of modulator M. The output circuit of modulator M is associated with line ML through a hand filter F The arrangement of the circuit at the receiving terminal of the system is similar to that described for the transmitting terminal and most of the apparatus used therein is identical with that used at the transmitting terminal. The elements at the receiving terminal corresponding to those at the trans mitting terminal have been des gnated with the same reference characters as used at the transmitting station with the addition of a The circuit at the receivin terminal differs from that at the transmitting terminal in the following particulars:

A receiving circuit R, instead of a transmitting circuit T, is adapted to be connected by the switch S with the channels 1' and 2' corresponding to the channels 1 and 2 at the transmitting station. The stationary electromagnets 7' and 10 corresponding to the recording electromagnets 7 and 10 at the transmitting terminal, act at the receiving terminal as reproducing magnets, while the movable electromagnets 9 and 12', corresponding to the reproducing electromagnets 9 and 12 at the transmitting terminal, act at the receiving terminal as recording electromagnets. Between the line 'ML and the contactor device 24' in channel 1' of the receiving terminal a band filter F is inserted. this filter being designed to pass the band of frequencies put on the line ML fromthe channel 1 at the transmitting terminal, and

! source of oscillations 0,, similar to the.

4 acsacee to exclude other frequencies. Similarly, a band filter F in channel 2' is associated with line ML, this band filter having the source of oscillations at the transmitting station.' The other elements terminal are identical with the s milarly designated elements at the transmitting ter-' mmal.

The band filters F at the transmitting terminal, and F, and F, at thereceiv ng terminal are used in the system for selectively transmitting waves of a particular range of frequencies and for suppressing transmission of waves of other frequencies. These filters may be designed in accordance with the principles disclosed in Campbell Patent No. 1,227.113, dated May 22, 1917., The modulator M may be of the balanced vacuum tube type, designed to suppress the unmodulated carrier such as is illustrated and described in U. S. patent to Carson No. 1,343,307, dated June 15, 1920. The demodulator D may be of the balanced vacuum tube type such as illustrated in- Fig. 49 of an' article entitled Carrier current telephony and tclcgra by published in the Transactions of the 1 merican Institute of Electrical Engineers, vol. 40, 1921. The source of oscillations O and may be of any suitable type as for example such as is disclosed in U. S. patent to Hartley No.

1,356,763, October 26, 1920.

Any of the well known methods may be used for synchronizing the apparatus at the transmitting and receiving terminals in the system shown in Figure 1. In the particular one illustrated, a source of energy E 511 plying energy to operate a motor S M at t e transmitting terminal at a desired speed is also utilized to supply energv which is transmitted over an auxiliary line L to operate the motor SM at the receiving terminal' in synchronism with the'motor S at the transmitting terminal.

The operation of the system of Figure -1 will now be described. During the interval of time corresponding to a half revolution of the commutator contactor 5, or one revo lution of the discs 8 and 11, the brushes 28 make contact with the metal ortion 26 of contactor 5, the circuit connecting battery 4 to electromagnet 3' thereby being closed and electromagnet 3 energized throughout this interval; The ener ization of electromagnet 3 causes switches 1 and S to be operated, and the circuits are then arranged as shown in Fig." 1. With the circuits s0 arranged the current through recording electromagnet 7 East the reproducing electromagnet 9 inat the receivingof the device TG, in channel 1 will be varied in accordance with the message variations received from transmitter circuit T. The recording electromagnet 7 impresses these cur-' rent variationson the telegraphone disc 8, and a permanent magnetic record of the variations are made on the disc 8 as it revolves past the stationary electromagnet 7 The magnetic record on the disc 8 as it revolves uces a current in that electromagnet, which as'this electromagnet is rotated in the same direction as the disc but at half its speed, will have a frequency range one-half that of the original variations received from transmitter circuit T, that is, each frequency v inthe frequency spectrum of the original} message variations has been reduced by this process to one-half of its original value. After one com lete revolution of the disc 8, or half a 'revo ution of the commutator of contactor 5, the magnetic record of the message variations received from transmitter circuit T extends completely around the disc 8, and only one-half of this record has been reproduced as the reproducing electr0mag-. net 9 is only revolving at one-half the speed of disc 8. At the end of the interval, the brushes 28 of contactor begin to make contact with the insulated portion 27 of contactor 5, the connection of battery 4 to electromagnet 3 being thereby broken so that electroma net 3 is de-energized. The switches 1 and S are thereby thrown in the .opposlte direction from their previous position so that transmitter circuit T is .disconnected from the recording electromagnet '7 of the device TGr in channel 1 and connected to the recordin electromagnet 10 of device TGr in channe 2, and erasing battery 23 is disconnected from the recording electromagnet 10 of device TGr and connected to the recordin electromagnet 7 of de-- vice TGr in channed 1. During the succeeding interval while the contactor 5 is making the last half of its revolution, disc 8 is making its second revolution andthe unrepr'oduced ortion of the magnetic record on that disc is eing reproduced at half speed by the reproducing electromagnet 9. Meanwhile, the erasing battery 23 is acting on electromagnet 7 so as to eiface the reproduced portion of the magnetic record on disc 8. At the end of the second revolution of disc 8 the magnetic recordmade thereon during 120 the first revolution has been completely reproduced and erased from the disc. Meanwhile, during' the interval corresponding to the last half revolution of the commutator of contactor 5.and the second revolution of 125 disc -8, themessage variations from the transmitter circuit T are being impressed on the recording electromagnet 10 of the device T622 in channel 2, recorded on the disc 11 and reproduced at half speed by the. reproducing electromagnet 12 in the same manner as described in connection with channel 1. When the magnetic record on disc 11 extends completely around disk 11, the switches S and 553 are thrown again in the opposite direction due to the brushes 28 again making contact with the metal portion 26 of contactor 5, and the cycle described above is repeated.

It will be apparent from the above that while the inputs to the fi-ecordinglectromagnets 7 and 10 in channels 1 and 2 respectivel due to the switching operation describe consisting of alternate blank and message intervals, the message variations in the outputs of reproducing magnets 9 and 12 in the respective channels will be continuous having a frequency range of one-half that of the ori inal message variations.

As the outputs o the two reproducing electromagnets 9 and 12 cover thefsame absolute frequency range, to avoid overlapping when they are transmitted over the line ML, the

variations in the output of magnet 9 in channel 1 is impressed directly on the line ML as shown, while the frequencies of the variations in the output of magnet 12 in channel 2 are raised by modulation before being impressed on the line ML.

It will be assumed for purposes of description that, as indicated in the figure, the transmitter circuit T generates message currents ranging from 0 to 3000 cycles, that oscillator 0 in channel 2 supplies a current of 1500 cycles to the input circuit of modulator M, that band filter F at the transmitting terminalhas a transmission range of 1500-3000 cycles, that band filters F and F in channels 1' and 2' respectlvely, at the receiving terminal have transmission ranges of 0-1500 cycles and 1500-3000 cycles, respectively. and that oscillator 0 at the receiving station supplies a current of 1500 cycles to the input circuit of demodulator D. Y

The half-speed message variations in the output of re roducing magnet 9 in channel 1 will, there ore, have a frequency range of 0-1500 cycles and, as shown in the Flgure 1, these variations are transmitted directly to the line ML. The half-speed message variations in the output of reproducing magnet 12 in channel 2 will also have a frequency range of 0-1500 cycles. These vanations are then combined in modulator M with the current of 1500 cycles from the oscillator 0 and a resultant band of 1500- 3000 cycles produced which is vselectively transmitted by filter F and sent out over the line ML. The total frequency range of the speech variations transmitted over theline ML including the frequency band of 04500 cycles from channel 1 and the fre- 1500-3000 cycles from chanquency band of the same as the frequency nel 2, is, then,

the recording electromagnet 9' of device TGr in that channel. The band of 1500- 3000 cycles selectively transmitted by filter F in" channel 2 iscombined in the demodulator Dwith the current of 1500 cycles from the oscillator 0 thereby reducing the frequenc1es in the band by the same amount that they were raised by modulation in the modulator M at the transmitting terminal. The resultant frequenc band 0150-1500 cycles in the output 0 demodulator D is ilrp pressed on the recording ,electromagnet of device TG' in channel 2.

The

message variations supplied to recording electromagnets 9 and 12 in channels 1 and 2, respectively,'are recorded'on discs 8 and 11 respectively, and reproduced by the reproducing electromagnets 7' and 10 scribed in connection with the operation of the similar elements at the transmittingterminal. In this case, the reproducing magnets 7 and 10' are stationary and the recording magnets 9 and 12 are rotated by motor SM, in the manner described for the corresponding elements at the transmit- .tlng terminal, in the same direction but at half the speed of the telegraphone discs 8 and 11. By the recording and reproducelectromagnets 7 and 10 at the transmitting terminal.

As the motors SM and SM at the trans mitting and receiving terminals respec tively, are operated in synchronism in the manner described if the phase relations of the elements of contractor device 5' and '9 respectively, in the same manner as was detelegra hone devices TG' and TG, are

proper y adjusted withrespect to the similarly designated elements at the transmitting terminal, the message intervals in the output of the reproducing electromagnets 7 and 10 at the receiving terminal by the operation of switch S aresupplied to the receiving clrcuit R in the proper order .to reproduce the same intelligible speech varia- ,of course,

tions as generated by the transmitter circuit T at the transmitting terminal.

Although the invention has been described and illustrated in connection with its use in wired transmission systems, it 1s,

applicable as well'to radio transmission. It is to be understood that the scopeof 'the invention is defined in the following claims, and that the invention 1s not band of frequency components, whlch method consists in dividing sa1d-message waves arbitrarily into sets of fragments on a time basis, reducing the frequency of each component of the successive fragments by a factor equal to the number of fragments in a, set, superposing the various fragments of a set, the components'of whichare changed in frequency, and transmitting together the super osedfragments.

2. he method ofsecuring secrecy in I transmission of a band .of message waves within substantially the frequency limits of said band comprising dividing said message waves arbitrarlly into sets of fragments on a time basis, reducing the frequency of each component of the successive fragments by a factor equal to the number of fragments in a set, superposingthe various fragments of 'a set the components of which are changed in frequencyfrand transmitting together the superposed agments within substantially the dfrequency limits of the original message an 3. The method of secret transmission of message waves having a band of frequency components, which comprises dividing said time basis, means to reduce the re message waves arbitrarily into sets ,of fragments on a time basis, reducing the fre uency of each component of the successive ragmentsv by a factor e ual to the number of fragments in a set, c an ing the frequency of each component in at east one fragment of each set so as to produce therein a band of frequency components lying outside the equency range 0 the bands of components of reduced frequency in the other fragments of the'set, superposing the various fragments of the set, and transmitting the superposed fragments within substantially the freuency limits of the original message band.

4 .1 In a secret signaling system, a source of message waves comprising a band of frequency components, means for dividing said message waves into sets of fra ments on a uency of each component of the successive agments to substantially one-half of 'its original value, means to increase the frequency of of. which have each component in at least one fragment of of message waves comprising a band of. frequency components, means for dividing said waves arbitrarily into sets of fragments on atime basis, means to reduce the frequency of each-component of the successive frag- 5. Ina secret signaling system, a source ments bya factor equal to the number of' fragments in a set, means to superposethe various fragments of a set, of wh ch are cha'n posed fragments.

6 Ina secrecy signaling system, means to generate message waves comprising a band of frequency component means for dividing said message waves arbitrarily into sets of fragments on a time basis, means to reduce the frequency of each component of the successive fragments by a factor equal to the number of fragments in a set, means to superpose the various fragments of a set, the components of which are changed in freuency, and means for transmitting together 1; e superposed fragments within substantially the frequency limits of the original message band.

7 A secret signaling system comprising a transmitting station, a receiving station and a transmission path therebetween, said transmitting station comprising means to generate message currents having a band of frequency components, means to arbitrarily divide said message currents into sets of fragments on a time basis, means for reducing each frequency component in the fragthe components 4 ed in frequency, and: means fortransmittingi together the superon sa1d receiving device in proper order to reproduce the original message.

v 8. In a secret signaling system, a transmita receiving station, and a trans therebetween, said transmitting ting station, mission path station comprising means for generating a message wave having a band of frequencies, means for separating said message waves into successive fragments on a time basis,

means for recording said successive fragments, and means finreproducing the recorded fragments, and transmitting them to said transmission path at a speed substantially half the speed at which said fragments were generated, said receiving station comprising a receiving device, means for recording the message fragments received over said.

line, means for reproducing the recorded fragments at a speed substantially "equal to the speedat which they were recorded at the transmitting station, and means to impress the reproduced fragments on said receiving device in the successive order in which they were roduced at the transmitting station.

9. if secret signaling system comprising a transmitting station, a receiving station, a transmission path therebetween, a pair of signaling channels at said transmittmg station, means to generate a message wave having a band of frequencies, means to direct successively produced portions of said wave alternately into said signalingu channels, means in each of said channels toreduce the frequency components in the received message portions to substantially one-half of their original values to make said message nels on said transmission path, a pair of re-' ceiving channels at' said receiving station,

means in said receiving channels for selecting said different frequency bands received over said transmission path, means in one the selected frequenc band therein so as to produce equivalent requency bands in the two receivmg channels, means to' increase each frequency in the equivalent frequency bands in the twovchannels to substantially twice its value, a receiving circuit and means to impress the bands of increased frequency in said receiving channels on said receiving c1rcu1t so as to reproduce the original message wave.

10. A secret signaling system comprising a transmitting .station,--"a; receiving station, a

transmission path therebetween, a air of signaling channels at said transmitting station, a source of signaling variations, means for alternately connecting said source to said channels, means in each of said channels for recording the received signaling variations, and reproducing them at substantially half the speed of recording, means for modulating a carrier wave in accordance with the reproduced variations in one of said chan;

nels to produce a band of frequencies lying outside the range of the band of reprodu frequencies in the other of said channels means for impressing the different bands 0 channels, and reproducing them at twicethe speed of recording, a receiving device and means for alternately connecting the outputs of said receiving channels to said receiving device so as to reproduce the original signaling variations.

In witness whereof, I hereunto subscribemy name this 6th day of Au of said receiving channels for demodulating 4 JOHN C. .S

st A. n. 1925. HELLEiIG.

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