US1753353A - Electrical system for secret transmission - Google Patents

Description

April 8, 1930. J. c. STEINBERG ELECTRICAL SYSTEM FOR SECRET TRANSMISSION Filed Oct. 18, 192'? ooowon 2 co m QQN Q mm m M mummn;

/M/N7'0/P JUHN [I STE/Mama 5r 1 TTORAfEY Patented Apr. 8, 1930 JOHN C. STEINBERG, OF EAST ORANGE, NEW JERSEY, ASSIGNOR T0 BELL TELEPHONE LABORATORIES, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK ELECTRICAL SYSTEM FOR SECRET TRANSMISSION Application filed October '18, 1927. Serial No. 226,857.

This invention relates to transmission sys-. tems and particularly to the method of and means for providing secrecy in the transmission of messages over said systems.

Systems for obtaining secrecy in signaling have heretofore been devised wherein the messages are obscured or rendered unintelligible, when received in the usual manner, by combining therewith noise frequencies.

This invention is based on this general principle, but the method of and means for generating the noise frequencies and their application to the message waves is accomplished in a novel manner.

This invention operates upon the princi ple that message waves may be masked or rendered unintelligible by applying to the ear of the listener at the proper instant, noise waves of the proper frequency and amplitude. Toprovide the proper frequency and instant of application of the noise waves, they are generated by the action of the message currents and impressed upon the transmission medium simultaneously with the message currents. No message waves can, therefore, be impressed on the transmission medium without their accompanying noise frequency waves, the latter varying in amplitude in substantially direct proportion with the amplitude of the message waves. I

It is an object of this invention to simplify the means for rendering messages unintelligible to persons unauthorized to receive them and simplify intelligible reception of messages by authorized persons.

A feature of this invention is the generation of the noise frequencies by the action of the message waves for combination with the message waves.

Another feature of the invention is the varying of the, amplitude of the noise frequencies in direct proportion to the amplitude of the message waves.

These objects and features and various advantages of this invention will be more fully understood in the following detailed description taken in connection with the accompanying drawing, the single figure of which shows a two way system embodying the in vention.

applying to the station operated for receiv- In the secrecy apparatus of this invention, as shown in the drawing, is a transmitter 8, the circuit of which is through energizing battery 9 and the primary of a four-winding transformer 10. Signals are received on a receiver 12 in circuit with the secondary of a three-winding transformer 13. The transformer 10 has three secondary windings, 15, 16 and 17, the secondary winding 15' being connected to the actuating winding of a voice operated relay 19. In series with this latter circuit is a condenser 20, and in shunt thereto an inductance 21 for the purpose of making the relay more sensitive to the average voice frequency currents.

The secondary winding 17 is in circuit with a winding 23 of transformer 13 and a winding 26 of transformer 27. The secondary winding 16 is in circuit with the lower armature of relay 19, filter F harmonic generator HG, filter F winding 29 of transformer 30, and the upper armature of relay 19. Mes sage and" noise frequency currents are impressed on, and received from a line L through winding 31 of transformer 30 and winding 28 of transformer 27. Across secondary 16 is shunted a variable resistance element 33 for varying the input into the harmonic generator HG. This harmonic generator may be avacuum tube rectifier such as disclosed in Patent No. 1,4463 52, February 27, 1923, and the filters F and F may be of the well known unbalanced type such as shown in Patent No. 1,227,113, May 22, 1917.

The operation of station A, the apparatus of which is set for transmitting is as follows: Voice frequency currents from transmitter 8 are impressed on secondary windings 15,16 and 17. The energy impressed on winding 15 operates the relay 19 and places the armatures thereof in the position shown in the drawing. The energy impressed on winding "17 passes onto the line L through transformer 27. The ener y impressed on winding 16 passes by way 0 the lower armature of relay 19 to the filter F This filter is constructed to pass only frequencies between 200 and 300 cycles per second. It is known that within this frequency range the fundamental of the female voice and the second harmonic of the male voice are to be found, so that this voice frequency reaches the harmonic generator-HG. The energy of this frequency wave depends upon the amplitude of the voice waves but it is always large enough to generate sufficient harmon-.

ics to mask the voice waves. As filter F has a range of 500 to 2000 cycles, only those har monics lying within this range are passed onto the line L through transformer 30 by way of the upper armature of relay 19.

This combination of voice and. noise frequency currents in unintelligible form may be transmitted between the two stations shown in any well known manner, for example, by the line L directly or by modulating a high frequency carrier wave with the lower frequencies for radio or wired transmission. In the case of radio transmission the line L would not of course, extend between the two stations but may be considered as leading from each station to suitable radio transmit ting and receiving apparatus.

, The operation of station B which is shown in condition to receive is as follows: The combination of message and voice frequencies is received on line L either directly in the case of radio or carrier transmission, or, from a suitable receiver, and impressed on transformers 27 and 30. From transformer 27 the unintelligible voice and noise frequency currents are impressed on transformer 13' through wind1ngs26 and 23'. However, part of the energy from the line L passes through transformer 30 by way of the lower armature of relay 19' to filter F Since the filters used in this system are of the-unbalanced type, the lower terminal of winding 29 is common with one input terminal of filter F so that the output of transformer'30' is impressed directly on filter F From this part of the received energy only the first harmonic of the male or the fundamental of the female voice frequency currents is passed by the filter F to the harmonic generator HG as in the case of F at station A. This generator produces the same harmonics as generator HG at station A and the filter F passes the same number of harmonics as filter F so that we have the same output waves at filter F as at filter F of the upper armature of relay 19. These noise frequencies are, however, impressed on this winding 180 out of phase with those arriving in winding 23. This is accomplished by winding the turns of winding 24: in the opposite sense to those of winding 23'. There is, therefore, a neutralization of the noise components in'the transformer 13 and the only energy impressed on the secondary winding of this transformer .is that of the message frequency waves generated in transmitter 8. The message is thus impressed on receiver 12' in intelligible form. Delay networks may also be employed in the output circuits of filters F and E to obtain the necessary phase opposition for neutralizing the masking noise requencies.

The invention is also susceptible to various other modifications and adaptations and accordingly is not to be considered as limited in any way by this particular disclosure.

What is claimed is:

1. In a signaling system, a source of mes sage waves, means for generating from said message waves noise waves having harmonics of said message waves, means for combining said noise waves with said message waves, and means at a distant receiving point for neutralizing said noise waves while retaining the message waves.

2. Ina signaling system, a source of message waves, a source of noise waves, a common output path for both of said sources, said output path being connected to said source of message waves, means included in said source of noise waves for producing said noise waves from said message waves, and means for combining said noise and. message waves, said last means comprising a relay operated by said messagewaves.

3. In a signaling system, a source of message waves, a source of noise waves, a common output path for both of said sources, said output pathbeing connected to said source of message waves, a harmonic generator for producingharmonics as noise waves from said message waves, said generatorbeing included in said sourceof noise waves inter posed between said source .of message waves and said output path, and means at a dismessage waves.

4. In a signaling system, a source of message waves, an output path connected to said source of message waves, a source of noise waves lnterposed between sa1d source of message waves and said output path, said source' of noise waves comprising a harmonic generator for producing noise waves which are harinonics of one of saidmessage waves, and a relay associated with said source of message waves for connecting said source of message waves to said source of noise waves.

5. In a secrecy system, a source of message frequency currents, a source of noise frequency currents, a harmonic generator controlled by the impression said message frequency currents thereon included in said source of noise frequency currents, an output path common to said noise frequency currents and said message frequency currents, and a voice operated relay actuated by said source of message frequency currents for making said system adaptable for combining and transmitting said message and noise frequency currents in unintelligible form and for controlling the impression of said message frequencycurrents on said harmonic generator.

6. In a secrecy system, in accordance with claim 5 in which said voice operated relay makes said system adaptable for receiving said combination of noise and message frequency currents or adaptable for combining said message and noise frequency currents and transmitting said combination thereof.

7. In a secrecy system, a source of message frequency currents, a source of noise frequency currents, means for combining said message and noise frequency currents, and means included in said source of noise frequency currents for selecting one frequency of the message currents, for generating from said one frequency, harmonics thereof for masking said message frequency currents, and means for eliminating the efiect of said harmonic frequency components from the mes: sage waves after transmission of the message waves and the noise waves to a distant point.

8. A method of masking intelligible message waves,-comprising first, selecting a component of said Waves, second generating harmonies from said component, and third combining said harmonics and said message waves in a common output path.

9. In a transmission system, an incoming line in which there is an unintelligible combination of message and noise frequency currents, receiver means on which said combination. is impressed, and a second means on which said combination is impressed, said second means generating from saidmessage currents the same noise frequencies as contained in said combination and impressing them on said receiver means in phase opposition to said noise frequency currents in said 11. A transmission system in accordance with claim it) which said receiver means com rises a three "winding transformer, said com ination being received on one winding thereof, and said noise harmonics being received on a second winding thereof, said second Winding being reversed with respect to said first mentioned winding.

12. la a signaling system, a source of message waves, means for generating noise Waves under control of said message waves, and a common output path for said message and said noise waves, said generating means including a harmonic generator for producing noise representing harmonics of a component of said message waves, the amplitudes of said harmonics being proportional to said component of said message Waves, and means for removing the harmonic frequency waves from the message Waves.

In witness whereofi I hereunto subscribe my name this 17th day of October, A. D., 1927.

JOHN C. STEINBERG.

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