US2034775A - Receiving system adapted to practice secret communication method - Google Patents

Description

rch 24, 1936. H, Q, RQOSENSTEIN 2,034,77

RECEIVING SYSTEM ADAPTED TO PRAICTICE SECRET COMMUNICATION METHOD Filed June 1.3, 1932 2 Sheets-Sheejn l INVENTOR HANS 0- ROOSENSTFJN .VBY I ATTORNEY 24, 936- H. 01 RQOSENSTEIN 4 2,034,175

RECEIVING SYSTEM ADAPTED TO PRACTICE SECRET COMMUNICATION METHOD Filed June 13, 1952 2 Sheets-Sheet 2 INVENTOR v 0- 300/1675 RNEY ATTO Patented Mar. 24, 1936 UNITED STATES PATENT OFFICE RECEIVING SYSTEM ADAPTED TO PRAG- TICE SECRET COMIMUNICATION METHOD ration of Germany Application June 13, 1932, Serial No. 616,905

r In Germany July 11, 1931 2 Claims.

This invention relates to a receiving system.

adapted to practice secret communication and is an additional improvement to the German Patent No. 521,991.

In the parent German Patent No. 521,991 a method fo-rsecret transmission on radio frequency waves has been disclosed in which the radio frequency wave modulated by the communication or signal is transmitted with a permanent disturbance (garbling action) in rapid succession. In this scheme two different waves are sent out while being changed in rapid succession, one of said waves being modulated by the signal, and the otherone by the garbling sound.

A better understanding of this invention will be had by referring to the accompanying drawings in which,

Fig. 1 is a circuit diagram of a receiver arrangement with two receivers tuned with respect to two different carrier waves.

Fig. 2 is a circuit diagram of a receiver arrangement similar to Fig. 1 except for the addition of an automatic gain control.

Fig. 3 is a circuit diagram of a transmitter arrangement having two transmitters whose carrier waves may be alternately modulated and the circuit is similar to Fig. 1 of the German Patent No. 521,991 mentioned above.

Fig. 1 shows a receiver arrangement adapted to coded or garbled communication of the kind before referred to in the above-mentioned German patent. There are provided two receivers El and E2 preferably of the super-regenerative type, which are tuned so as to respond to the two carrier waves of the transmitters. Before discussing the receiver arrangement a brief extract of the parent German Patent 521,991 will now be given. If the secret communication system is to be employed in wireless transmission, there are provided at the transmitting end two distinct transmitters which are indicated by Fig. 3 as S1 and S2, whose carrier waves may be alternately modulated by means of a transformer T by the voice to be transmitted or from the alternating current source by a disturbing or jamming frequency. Such alternate modulation by the voice and garble notes is maintained by two permanently operating change-over relays or switches R which serve to connect alternately and in rapid succession the voice and garble-note supply leads S1 and S2. The electrical control of the relay R is eifected, for instance, by a device U which may consist of a synchronous motor M operated from the alternating current source W and. a contact disc K, the latter supplying current to the relay switch R from the battery B at a rate or rhythm determined by the disposition of the contacts upon the contact disc K. Now referring again .to the receiver'arrangement, the output ends of the receivers are alter nately connected to the translating device H by means of relays R so that they come to act upon the listening or translating device H alternately. Each receiver is excited by the corresponding receiver antenna which is suitably tuned to its wave. The relay switches R controlled by the relay windings are so disposed thatwhen the brush sliding over (or being in frictional contact with) the commutator disc K happens to get on a contact thereof so that the two relay windings are energized, one switch R, say, the upper one is thrown over to the left-hand side, and the other one to the right, while with unenergized relay windings the positions of the two switches are correspondingly altered. While in the transmitter arrangement, the switches of the relays R connect the inputs of the two transmitters S1 and S2 alternately with the modulation source T and with the jamming generator (interference note generator) W, it will be seen that in the receiver arrangement the switches R of the relays connect the outputs (plate circuit of the last stage) of the receivers El and E2 alternately with the telephone receiver H and the suitable synchronizing device of the motor M. At the instant when, for instance, the transmitter S1 working in the wave M is modulated by voice currents (lefthand position of the upper switch R), while the transmitter S2 working on the wave A2 is modulated by the disturbing or jamming notes of the generator W, it will be seen that at the receiving point, because of the synchronism of its commutator disc K and the similar disc at the sending end, the upper switch R of the receiver equipment is in the left-hand and the lower switch R in the right-hand position. The receiver E1 tuned to the wave M, as will be seen, has its output end connected with the telephone receiver H which receives the ungarbled communication, while the output of the receiver E2 tuned to wave k2, by way of the lower switch R shifted to the right, controls the synchronizing means of the driving motor M of the receiver equipment. If upon further motion of the two discs K the two transmitters owing to throw-over of the switches R interchange their parts so that transmitter S2 will operate as a regular signal transmitter and the transmitter S1 as a jammer or garbler, it will be seen that incidentally, due to the throw-over of the switches at the receiving end, also the two receivers reverse their parts so that receiver E2 now works upon the telephone receiver, and receiver E1 on the synchronizing means of the motor M. The interfering tone is continuously passed on to the synchronous motor Mby means of the reed of the relays or switch R as indicated at the bottom. In presuming that this interfering tone contains an alternating current-component, a

synchronism between motor and reversing mechanism will hereby be obtained at the transmitter side. It is obvious that the alternating currentcomponent necessary for synchronizing the motor, may be present in the interfering tone in a great many ways. In the simplest embodiment, the interfering tone is simply formed as sinusoidal alternating current synchronizing the motor M. If the disturbing or jamming sound is used at the same time for the synchronization of the reversing or throw-over switching means at the receiving and the transmitting ends, the synchronizing machine M is used therefor, the latter actuating a contact-maker disk K. It has been found that in the practical application of this method in short-wave telephony a flicker in the incoming volume is produced by fading actions upon the two radio frequency channels intended for the communication. It is a well-known fact that fadings generally differ for different frequencies with the result that the signal reaching the receiver end in rapid alternation upon the two frequencies, experiences permanent variations in volume. Since fading as a general rule does not occur simultaneously on waves of dissimilar length, in a method of secret or code telephony as disclosed in the above mentioned German patent, rapid variations in the reproducing sound-volume will be occasioned by the fading phenomena, and these are due to the signals which arrive alternately by way of the two frequency channels, are liable to differ widely in their intensity. This difference in the incoming volumecaused by or due tothe two channels manifests itself in the form of interruptions in the rhythm of the change-over frequency between both channels, and this is liable to impair intelligibility to a large degree. This condition will no longer arise by use of this invention. Furthermore, this is the object of the new application.

Now, according to this invention, in order to overcome this trouble, automatically acting gain regulator means are provided at the receiving end as indicated at VI and V2, in Fig. 2. One drawback to the above mentioned arrangement is that the standard amplifying regulation means have an ever-present electric inertia. If the inertia were of zero value it would be impossible to insure with such an arrangement the reproduction of a modulated signal for the reason that each and every modulation is equalized by the gain control. In order to avoid this an automatic gain control of the customary form must involve a time-constant which is greater than the period of the lowest frequency to be transmitted as noted in rapid fading disturbances. It will be seen that if the reproducing sound volume of the signals coming in by way of the two channels is at all times kept stable or equal by the use of fading compensation means, improved reception will result. (It has been discovered that the super-regenerative receiver has the property of being hardly a function for its volume of the intensity of the incoming modulated signal, while its reproducing volume is primarily dependent upon the degree of modulation of the incoming radio frequency waves. The independence of the volume of the super-regenerative receiver from the field strength of the incoming signal has been ascertained by observation; even in case of very rapid changes of the input field strength, for instance at sudden disconnection of the transmitter, the receiver becomes practically without inertia so sensitive that the delivered volume does not change. In the practical application this takes place in such manner at the shutting off of the transmitter that the disturbances present, produced by the heat and shot action, are amplified so as to have approximately the same volume as the modulated receiving signal originally present. As has been observed, the mechanism functions entirely without inertia. The cause is to be seen in the logarithmic demodula tion characteristic of the super-regenerative-receiver, whereby, as is known by the prior art, for example see German Patent No. 560,227, an amplitude-independent receiving volume is produced. In other words, a super-regenerative receiver operates like a volume regulator free from the sluggishness caused by the electrical inertia, so that the super-regenerative receiver is most eminently suited for use inside the scope of the present invention and may be employed without resorting to the use of an automatic volume control.

I claim:

1. In a secret signaling system comprising two super-regenerative receivers tuned to respond to signals of two different channels, automatic relay means for alternately connecting the output ends of said receivers to a translating device, a contacting make-and-break disc arranged to break the actuating circuit of said relays.

2. In a short wave signaling system comprising two super-regenerative receivers tuned to respond to signals of two different channels, automatic relay means for alternately connecting the output ends'of said receivers with a translating device, said automatic relay means comprising a contacting make-and-break disc, a motor for revolving said disc.

HANS OTTO ROOSENSTEIN.

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