Communication system

Abstract

In a pulse code modulation system, a source of key signals comprising a source of random pulses, multisection delay device, means for applying said pulses to said multisection delay device, apparatus for combining the outputs of predetermined sections of said delay device and apparatus for enciphering pulse code modulation signals by combining said signals with said combined output from said sections of said multisection delay device.

Claims

What is claimed is:

1. In a pulse code modulation system, a source of key signals comprising a source of random pulses, multisection delay device, means for applying said pulses to said multisection delay device, apparatus for combining the outputs of predetermined sections of said delay device and apparatus for enciphering pulse code modulation signals by combining said signals with said combined output from said sections of said multisection delay device.

2. Apparatus for generating key pulses for enciphering pulse code modulation signals comprising a source of random signals, a multielement delay device for securing different delay times, means for transmitting said random signals through said multielement delay device, combining circuits for combining said random pulses after delays of different amounts to secure key pulses for ciphering pulse code modulation signals and apparatus for automatically changing the delay intervals of said random pulses for combination.

3. Apparatus for gnerating key pulses for enciphering pulse code modulation signals comprising a source of random signals, a multielement delay device for securing different delay times, means for transmitting said random signals to said multielement delay device, combining circuits for combining said random pulses after delays of different amounts to secure key pulses for ciphering pulse code modulation signals, and a stepping switch interconnected between the elements of said delay device and said combining circuit for interchanging the connections whereby the random pulses are combined after different delay intervals.

4. Apparatus for generating key pulses for enciphering pulse code modulation signals comprising a source of random signals, a multielement delay device for securing different delay times, eans for transmitting said random signals through said multielement delay device, combining circuits for combining said random pulses after delays of different amounts to secure key pulses for ciphering pulse code modulation signals, a plurality of contacts controllable in accordance with perforations in the flexible medium, connections between said contacts and said combining apparatus for changing the interconnections under control of perforations in the said tape.

5. In a secret communication system, means for representing a signal wave by code groups of signals, each signal of which may comprise any one of a plurality of different characteristics, a signal transmission medium, means for transmitting pulse signals over a transmission medium, receiving apparatus connected to said medium comprising means for decoding pulse code groups of signals each signal of which may comprise any one of a plurality of different characteristics, cipher key generating equipment located at each end of said transmission medium comprising a multisection delay device, apparatus for generating random pulses and applying them to said delay device at the first end of said medium, apparatus for transmitting the characteristics of said pulses over said medium, other eqipment for regenerating pulse similar to the pulses applied to said delay devices at said first end and applying the regenerated pulses to corresponding delay devices at the receiving end of said medium, apparatus at each end of said medium for combining said random pulses in identical manner after predetermined different delays which delays are identical at both ends of said medium, and means for enciphering said code modulation signals at the first end of said medium under control of said combined signals, and means for deciphering said enciphered signals at the receiving end of said medium under control of identical pulses as combined by said combining apparatus at the first end of said medium.

6. In a secret communication system, means for representing a signal wave by code groups of signals, each of which may have any one of a plurality of different characteristics, a signal transmission medium, means for transmitting pulse signals over a transmission medium, receiving apparatus connected to said medium comprising means for decoding pulse code groups of signals each of which may comprise any one of a plurality of different characteristics, cipher key generating equipment located at each end of said transmission medium comprising a multisection delay device, apparatus for generating random pulses and applying them to said delay device at the first end of said medium, apparatus for transmitting the characteristics of said pulses over said medium, other equipment for regenerating the pulses similar to the pulses applied to said delay devices at the first end of said transmission medium and applying the regenerated pulses to corresponding delay devices at the receiving end of said medium, apparatus at each end of said medium for combining said random pulses in identical manner after predetermined different delays which delays are identical at both ends of said medium, and means for enciphering said code modulation signals at the first end of said medium under control of said combined signals, means for deciphering said enciphered signals at the receiving end of said medium under control of identical pulses as combined by said combining apparatus at the first end of said medium, apparatus located at both ends of said medium for automatically changing the delay intervals of the pulses which are combined, means for causing said changes to be made substantially simultaneously at both ends of said medium.

7. In a secret communication system, means for representing a signal wave by code groups of signals, each of which may have any one of a plurality of different characteristics, a signal transmission path, means for transmitting pulse signals over a transmission path, receiving apparatus connected to said path comprising means for decoding pulse code groups of signals each of which may comprise any one of a plurality of different characteristics, cipher key generating equipment located at each end of said transmission path comprising a multisection delay device, apparatus for generating random pulses and applying them to said delay device at the first end of said path, apparatus for transmitting the characteristics of said pulses over said path, other equipment for regenerating pulses similar to the pulses applied to said delay devices at the first end of said path and applying the regnerated pules to corresponding delay devices at the receiving end of said path, apparatus at each end of said medium for combining said random pulses in identical manner after predetermined different delays which delays are identical at both ends of said path, and means for enciphering said code modulation signals at the first end of said path under control of said combined signals, means for deciphering said enciphered signals at the receiving end of said path under control of identical pulses as combined by said combining apparatus at the first end of said path, a plurality of contacts at each end of said path, means for controlling said contacts in accordance with physical conditions recorded in a storage medium, interconnections between said contacts and said delay devices and between said contacts and said combining apparatus for interchanging the connections between said combining apparatus and said delay devices under control of the physical conditions stored in said medium, and appatus for advancing said medium substantially simultaneously at both ends of said transmission path.

8. In a secret communication system, means for representing a signal wave by code groups of signals, each of which may have any one of a plurality of different characteristics, a signal transmission path, means for transmitting pulse signals over said transmission path, receiving apparatus connected to said path comprising means for decoding pulse code groups of signals each of which may comprise any one of a plurality of different characteristics, cipher key generating equipment located at each end of said transmission path comprising a multisection delay device, apparatus for generating random pulses and applying them to said delay device at the first end of said path, apparatus for transmitting characteristics of said pulses over said path, other equipment at the receiving end of path for regenerating pulses similar to the pulses applied to said delay devices at the first end of said path and applying them to corresponding delay devices at the receiving end of said path, apparatus at each end of said path for combining said random pulses in identical manner after predetermined different delays which delays are identical at both ends of said path, and means for enciphering said code modulation signals at the first end of said path under control of said combined signals, means for deciphering said enciphered signals at the receiving end of said path under control of identical pulses as combined by said combining apparatus at the receiving end of said path, a plurality of contacts at each end of said path, a storage medium means for controlling said contacts in accordance with physical conditions recorded in a storage medium, interconnections between said contacts and said delay devices and between said contacts and said combining apparatus for interchanging the connections between said combining apparatus and said delay devices under control of the physical characteristics stored in said medium, apparatus for advancing said medium substantially simultaneously at both ends of said transmission path, apparatus for preventing transmission of signal pulses under control of said coding apparatus over said transmission path during the advance of said storage medium.

9. In a secret communication system, means for representing a signal wave by code groups of signals, each of which may have any one of a plurality of different characteristics, a signal transmission path, means for transmitting pulse signals over said transmission path, receiving apparatus connected to said path comprising means for decoding pulse code groups of signals each of which may comprise any one of a plurality of different characteristics, cipher key generating equipment located at each end of said transmission path comprising a multisection delay device, apparatus for generating random pulses and applying them to said delay device at the first end of said path, apparatus for transmitting the characteristics of said pulses over said path, other equipment for regenerating the pulses similar to the pulses applied to said delay devices at said first end of said path and applying the regenerated pulses to corresponding delay devices at the receiving end of said path, apparatus at each end of said path for combining said random pulses in identical manner after predetermined different delays which delays are identical at both ends of said path, and means for enciphering said code groups signals at the first end of said path under control of said combined signals, means for deciphering said enciphered signals at the receiving end of said medium under control of identical pulses as combined by said combining apparatus at the first end of said path, a plurality of contacts at each end of said path, a storage medium means for controlling said contacts in accordance with physical conditions recorded in a storage medium, interconnections between said contacts and said delay devices and between said contacts and said combining apparatus for interchanging the connections between said combining apparatus and said delay devices under control of the physical characteristics stored in said medium, apparatus for advancing said medium substantially simultaneously at both ends of said transmission path, apparatus for preventing the transmission of signaling pulses over said transmission path under control of said combined and variously delayed random pulses during the changing of said connections under control of said flexible storage medium.

10. In a communication system, apparatus for generating code groups of pulses representing information to be transmitted, enciphering apparatus comprising means for generating ciphered key signals for enciphering and deciphering said code signals, connections within said means to control the key signals generated thereby, apparatus for automatically varying said interconnections within the said key generating equipment for changing the key pulses generated thereby, and apparatus to suppress the transmission of pulses under control of either of said code groups of pulses or said key generating pulses during the time said interconnections are being changed.

11. A pulse code modulation system comprising a source of voice frequency currents, apparatus for representing said voice frequency currents by means of code groups of signals occurring in rapid succession, a source of key signals, means for enciphering said code signals by means of said key signals, storage means having cipher changing information stored therein, apparatus for controlling generation of said key signals in accordance with information stored in said storage means.

12. A pulse code modulation system comprising a source of voice frequency currents, apparatus for representing said voice frequency currents by means of code groups of signals occurring in rapid succession, a source of key signals, means for enciphering said code signals by means of said key signals, an enciphering storage medium having cipher control information stored therein, apparatus for controlling generation of said key signals in accordance with information stored in said storage means, and apparatus for advancing said storage medium at a slower rate than said code groups of signals.

13. In a pulse code modulation system enciphering means comprising enciphering control tape, a source of key signals, means for controlling the generation of said key signals by said control tape and enciphering apparatus for enciphering pulse code modulating signals under the control of said key signals.

14. In a pulse code modulation system comprising apparatus responsive to enciphered pulse code modulation signals, deciphering apparatus comprising a ciphering storage tape having cipher control information stored therein, a source of key signals controlled by said storage tape and means for deciphering said enciphered signals under control of said key signals.

15. In a pulse code modulation system a source of enciphering signals comprising a source of random signals, a stepping device and apparatus for changing the connections to said source by means of said stepping device and means for combining said random signals with said pulse code modulation signals.

16. In a pulse code modulation system a source of enciphering key signals comprising a source of random signals, a stepping device and apparatus for changing the connections to said source by means of said stepping device and means for combining said random signals with said pulse code modulation signals, deciphering apparatus comprising means for generating a second series of key signals identical with first series of key signals including a stepping device, means for advancing said second stepping device incident to the advance of said first stepping device.

17. In a pulse code modulation system a source of enciphering key signals comprising a source of random signals, a stepping device and apparatus for changing the connections to said source by means of said stepping device and means for combining said random signals with said pulse code modulation signals, deciphering apparatus comprising means for generating a second series of key signals including a second stepping device, and means for advancing said two stepping devices substantially simultaneously.

18. In a high speed secrecy system, apparatus for generting key signals comprising a source of noise currents, deriving pulses having random characteristics and durations therefrom, apparatus operating at high speed for combining said pulses to form enciphering key pulses, and other apparatus operating at a slower rate for changing the manner in which said pulses are combined.

19. In a high speed secrecy system apparatus for generating key signals comprising a source of noise currents, means for deriving pulses having random characteristics and durations therefrom, apparatus operating at high speed for combining said pulses to form enciphering key pulses other apparatus operating at a slower rate for changing the manner in which said pulses are combined, comprising a storage medium having cipher changing information stored therein and apparatus controlled by said storage medium for controlling the manner in which said random pulses are combined in a secrecy system.

20. Apparatus for generating enciphering key pulses comprising a source of noise currents, a tapped delay line supplied with currents controlled by said noise currents and apparatus for combining the outputs from a plurality of said taps to form enciphering key signals.

21. In a high speed secrecy system apparatus for generating key signals comprising a source of noise currents, means for deriving pulses having random characteristics and durations therefrom, apparatus operating at high speed for combining said pulses to form enciphering key pulses other apparatus operating at a slower rate for changing the manner in which said pulses are combined, comprising a stepping device and apparatus controlled by said stepping device for controlling the manner in which said random pulses are combined in a secrecy system.

22. Apparatus for generating enciphering key pulses comprising a source of noise currents, a tapped delay line supplied with currents controlled by said noise currents and apparatus for combining the outputs from a plurality of said taps to form enciphering key signals, a stepping device for selecting the taps from which the output is to be combined.

23. In a secret communication system a transmitting station, a receiving station, a communication path interconnecting said stations, a source of noise currents at said transmitting station, apparatus for deriving random pulses from said noise currents, means for transmitting the significant characteristics of said pulses over said transmission path, apparatus responsive to transmission of said significant characteristics over said transmission path for regenerating an identical series of random pulses at said receiving station, enciphering and deciphering pulse generating equipment at said transmitting and receiving stations comprising a tapped delay line, means for supplying said random pulses to said delay line at said stations and apparatus for forming ciphering key signals by combining the output of selected taps which are identical at both of said stations.

24. In a secret communication system a transmitting station, a receiving station, a communication path interconnecting said stations, a source of noise currents at said transmitting station, apparatus for deriving random pulses from said noise currents, means for transmitting the significant characteristics of said pulses over said transmission path, apparatus responsive to transmission of said significant characteristics over said transmission path for regenerating an identical series of random pulses at said receiving station, enciphering and deciphering pulse generating equipment at said transmitting and receiving stations comprising a tapped delay line, means for supplying said random pulses to said delay line at said stations, apparatus for forming cyphering key signals by combining the output of selected taps which are identical at both of said stations, a stepping device located at each of said stations for selecting the taps the output of whch is combined, and means for advancing said stepping device substantially simultaneously at both of said stations.

25. In a secret communication system a transmitting station, a receiving station, a communication path interconnecting said stations, a source of noise currents at said transmitting station, apparatus for deriving random pulses from said noise currents, means for transmitting the significant charcteristics of said pulses over said transmission path, apparatus responsive to transmission of said significant characteristics over said transmission path for regenerating an identical series of random pulses at said receiving station, enciphering and deciphering pulse generating equipment at said transmitting and receiving stations comprising a tapped delay line, means for supplying said random pulses to said delay line at said stations and apparatus for forming ciphering key signals by combining the output of selected tape which are identical at both of said stations, a stepping device located at each of said stations for selecting the taps the outpt of which is combined and means for advancing said stepping device substantially simultaneously at both of said stations, apparatus for preventing the transmisson of significant signals over said transmission path during the time said characters are being changed.

26. In a communication system means for masking the communication currents comprising a source of noise currents having frequency components outside the frequency range of said communication currents, apparatus for eliminating from said noise currents all component currents having a frequency range within the frequency range of said communication currents and apparatus for combining the remaning noise currents with said communication currents.

27. In a communication system means for masking the communication currents comprising a source of noise currents having frequency components outside the frequency range of said communication currents, apparatus for eliminating from said noise currents all component currents having a frequency range within the frequency range of said communication currents and apparatus for combining the remaining noise currents with said communication currents, receiving equipment responsive to said communication currents and apparatus for suppressing currents having frequencies of said noise frequency currents.

28. In a pulse code modulation signaling system a source of signaling currents, a source of cipher key signals, a source of noise currents having frequencies outside said signaling frequency range means for suppressing all frequency components of said noise currents within said signaling frequency range, apparatus for employing said signaling currents and said noise currents for controlling the generation of pulse code modulation signals, means for combining said pulse code modulation signals with said key cipher signals, deciphering and decoding apparatus for recovering said noise and signaling currents and filter means for separating said noise currents from said signaling currents.

29. In a pulse code modulation system a plurality of double stability circuits, apparatus for supplying received pulses to said circuits in rotation, means for causing said circuits to change their condition of stability in response to the application of pulses having predetermined characteristics to said double stability circuits, apparatus for interrupting transmission of said pulse code modulation system at intervals and means for restoring all of said double stability circuits to a predetermined condition of stability during said interruptions.

30. In a secrecy system a transmitting station, a receiving station, a communication path extending between said stations which path is susceptible to unauthorized monitoring, a source of key signals at each of said stations comprising apparatus for generating identical series of random pulses at each of said stations and a stepping device for controlling the random signal pulses generated at each of said stations, apparatus for enciphering signals under control of said key pulses at said transmitting station, other apparatus for deciphering said signals under control of said key pulses at said receiving station, apparatus for advancing said stepping devices step by step substantially simultaneously at both of said stations, apparatus for interrupting transmission of communication currents during the advancing of said stepping device.

31. In a secrecy system a transmitting station, a receiving station, a communication path extending between said stations which path is susceptible to unauthorized monitoring, a source of key signals at each of said stations comprising apparatus for generating identical series of random pulses at each of said stations and a stepping device for controlling the random signal pulses generated at each of said stations, apparatus for recovering signals under control of said key pulses at said transmitting station, other apparatus for deciphering said signals under control of said key pulses at said receiving station, apparatus for stepping said stepping device substantially simultaneously at both of said stations, apparatus for interrupting transmission of communication currents during the stepping of said stepping device, apparatus for restoring receiving circuits at said receiving station of a predetermined condition during the operation of said stepping device.

32. In a communication system for the transmission of complex signaling waves, apparatus for representing changes in amplitude of the signaling wave between predetermined instants of time by means of code groups of pulses, a source of cipher key signals and apparatus for combining said ciphered key signals with said pulses and means for recovering said differences in amplitude and reconstructing a complex wave form therefrom.

33. In a pulse code modulation system, a source of pulse code modulation signals, comprising code groups of pulses representing the amplitude of the complex wave form at discreet instants of time, translating apparatus for translating said code groups of pulses into other pulses representing a change in amplitude of said complex wave between said discreet instants of time, a first source of cipher key signals, means for enciphering said signals representing differences in amplitude under control of said cipher key signals, a second source of signals for generating cipher key signals identical with said first group of cipher key signals and means for deciphering said enciphered signals under control of signals from said second source of cipher key signals, and means for recovering said complex wave form from said deciphered signals.

34. In a communication system, apparatus responsive to a complex signaling wave form for generating code groups of signals representing the difference in amplitude of said complex wave form at discrete instants of time, a communication path, means for transmitting said signals over a communication path, apparatus for recovering said complex wave form from said signals and apparatus for periodically restoring the output of said apparatus for recovering the complex wave form to a predetermined level.

35. In a pulse code modulation system, modulating equipment for representing differences in amplitude of an applied signaling wave by means of code groups of signaling conditions, demodulating equipment responsive to code groups of signaling conditions for recovering said differences in amplitude, means for reconstructing the signaling wave from said differences in amplitude, apparatus for periodically simultaneously resetting said modulation and demodulation equipment to predetermined reference conditions.

36. In a communication system apparatus for representing changes in an applied signaling wave by means of signaling pulses, apparatus for recovering said changes in amplitude from said signaling pulses, means for reconstructing the signaling wave from said recovered changes, apparatus for periodically interrupting the operation of said system and applying a predetermined reference input level, other apparatus for restoring said reconstructing apparatus to a corresponding reference level.

37. In a pulse communication system, apparatus for representing changes in amplitude of a signaling wave between discrete instants of timwe by means of pulses, means for periodically interrupting said apparatus for predetermined intervals of time, and means for restoring said apparatus to a pedetermined condition during said interruption intervals.

38. In a pulse communication system, apparatus responsive to groups of pulses representing differences in signal amplitude of an applied signal wave, means for recovering the differences represented by said pulses, and other apparatus for reconstructing the signal wave from said differences, apparatus for periodically restoring said reconstructing apparatus to a predetermined reference condition.

Description

This invention relates to a communication system and more particularly to a communication system in which complex wave forms are transmitted by code groups of pulses transmitted at rapidly recurring instants of time.

An object of this invention is to provide an improved and simplified means and methods for representing complex wave forms by means of code groups of different signaling conditions which improved means and methods are capable of operating at high speed.

Another object of this invention is to add random noise currents to the complex wave form before it is represented by the code groups of pulses in such a way that the noise effectively masks the nature of the complex wave form and the intelligence conveyed thereby after it is represented by the code groups of pulses but at the same time does not in any way interfere with or add to the actual complex wave form which may be recovered at receiving stations free and independent of the added noise.

Still another object of this invention is to provide an improved ciphering method and arrangement for enciphering coded groups of pulses in such a manner that they may not be understood unless they are transmitted through deciphering equipment which is complementary to or cancels the effects of the enciphering equipment at the transmitting station.

Another object of this invention is to provide deciphering equipment which is capable of deciphering enciphered code groups of pulses and recovering the original code groups of pulses.

Another object of this invention is to provide improved decoding equipment which is capable of operating at high speed for recovering the complex wave form represented by coded groups of difference signaling conditions of short duration occurring in rapid succession.

A feature of this invention relates to a cathode-ray tube which is capable of substantially continuously and instantaneously representing a complex wave form by a complete code group of different signaling conditions. The cathode-ray tube is of a type which is provided with a target and electrodes which at substantially all times have applied to them electrical conditions representing a complete code group, determined by the instantaneous amplitude of the complex wave form.

Another feature of this invention relates to a cathode-ray coding tube wherein the coding target is arranged to cause certain codes, i.e., the end codes, to be extended so that these codes will be formed when the applied signal exceeds the operating range of the tube.

Features of the coding tube disclosed but not claimed herein which are novel are claimed in my copending application Ser. No. 37,035 filed July 3, 1948.

Another feature of this invention relates to circuits and apparatus and methods of changing code groups of pulses of one code into code groups of pulses of a different code.

Another feature of this invention relates to circuits, apparatus and methods of changing from a second coded group of pulses back to the first code group of pulses.

Another feature of this invention relates to methods, circuits and apparatus for periodically checking and automatically setting the translating circuits.

Another feature of this invention relates to equipment for changing a code group of signaling conditions simultaneously present at an instant of time into a code group of signaling conditions occurring one after another in sequence by means of transmitting the signaling conditions through delayed networks, lines or devices having different delay intervals.

Another feature of this invention is to combine pulses of different signaling conditions received in sequence one after another into a single pulse by transmitting the various pulses received through delayed networks, lines or devices of different delay intervals so that pulses arrive at the output of the delay devices substantially simultaneously.

Another feature of this invention relates to switching equipment for readily connecting or disconnecting ciphered equipment both at transmitting and receiving ends of the system.

Another feature of this invention relates to key generating equipment for generating ciphered key signals for enciphering and deciphering pulse code groups of pulses of different signaling conditions.

A feature of this invention relates to employing noise currents to generate a series of random pulses of different signaling conditions for controlling the key generator.

Another feature of this invention relates to transmitting random pulses of different signaling conditions along a delayed network, line or device and employing the pulses after different delay intervals for controlling the generation of a series of ciphered keying pulses of different signaling conditions.

Another feature of this invention is to provide switching means having a large number of permutations of selectable orders and times for employing the random pulses from the noise generating equipment.

Another feature of this invention relates to a switching device capable of being arranged in a large number of different permutations which may be changed step by step in any random manner for further selecting the order and times of using the various noise control pulses.

Another feature of this invention is apparatus and equipment for employing a stepping switch controlled by a perforated punched or embossed tape for further increasing the number of permutations and random characteristic of the noise pulses.

Still another feature of this invention relates to control equipment for actuating the stepping switch and the tape controlled switch in any suitable manner.

Another feature of this invention relates to control equipment for suppressing the transmission of signaling conditions during the time the connections within the key generating equipment are being shifted thus preventing the transmission of either key signals or unciphered pulses.

Another feature of the invention is directed to equipment for starting the key equipment at both the transmitting and receiving stations in synchronism.

Briefly, in accordance with the invention described herein, a complex wave form is employed to control the generation of code signals. The magnitude or amplitude of a complex signaling wave, such as a speech wave, telegraph wave, frequency division multiplex signals, time division multiplex signals, or other complex signaling wave is represented by means of code groups of signals each signal of which may comprise any number of a plurality of different signaling conditions.

While the invention described herein is not limited to any particular code or groups it is usually convenient to employ a uniform code each code group of which has the same number of signals and each code group of which represents a predetermined amplitude of the complex signaling wave. That is, each code group is of a uniform number of different signals or a predetermined number of pulses in which each of the signals or pulses may comprise signaling conditions of any of a plurality of different signaling conditions.

In the specific embodiment set forth herein it is assumed that these code groups may comprise five or less signals or pulses and that each pulse or signal may comprise either one of the two signaling conditions may be transmitted during the time assigned to the various pulses or pulse positions.

In such a system any suitable code may be employed wherein the different code groups are assigned to represent the different amplitudes of the complex wave form. In the specific embodiment set forth herein the coding and decoding equipment is arranged to generate and respond to the binary code in which each of the signals or pulses represents or is analogous to a digital position of a binary number and one signaling condition represents one magnitude of a digit and the other signaling condition represents another magnitude of a digit.

In order to more readily describe and follow the various signals and signaling conditions employed in forming and transmitting code groups of signaling conditions, pulses of one character are frequently called marking pulses, on pulses, or current pulses while the pulses of the other signaling condition are frequently called spacing pulses, off pulses, or pulses of no current. Sometimes these two pulses are called positive pulses and negative pulses. The signals or signaling conditions as they are being transmitted through the various circuits and apparatus of the system may be represented by different signaling conditions. It is frequently most convenient to refer to each pulse as marking or spacing signals.

In accordance with the present invention the code groups of signals may be all generated substantially instantaneously under control of the complex wave or they may be generated at predetermined times in rapid succession so that the amplitude of the complex signaling wave can be represented by a group of signals or pulses occurring at a plurality of rapidly recurring instants of time. The rapidity of the recurrences of the code groups representing any complex signaling wave determines the highest frequency component of the signaling wave which may be transmitted over the system. In general, the frequency of this component is somewhat less than half the highest recurrence rate of transmitted pulse or signal groups representing the amplitude of the complex wave. Thus, for example, if it is desired to transmit a frequency range of up to 5,000 to 5,500 cycles then the coding equipment should generate complete code groups of pulses or signal conditions at a rate of at least 12,000 codes each second.

It is to be understood, of course, that any suitable frequency range may be employed.

The foregoing objects and features of this invention, the novel features of which are specifically pointed out in the claims appended hereto, may be more readily understood from the following description when read with reference to the attached drawings in which:

FIG. 1 shows the manner in which FIGS. 2 and 3 are arranged adjacent one another;

FIGS. 2 and 3 show in outline form the various elements of an exemplary system embodying the present invention. FIG. 2 shows the various elements in the manner in which they cooperate one with another at the transmitting station or end of the system, while FIG. 3 shows the manner in which the various elements of the system cooperate with each other at the receiving or distant end of the system. As shown in FIGS. 2 and 3, as well as in other figures of the drawing, the equipment and apparatus required for the transmission of the signals or complex wave form in one direction only is shown in the drawing. It is to be understood, however, that this equipment will be duplicated for transmission in the opposite direction and that equipment such as shown in the drawing together with a duplicate thereof for transmission in the opposite direction may be readily combined in a well-understood manner to provide a two-way transmission path between the ends of the system;

FIG. 4 shows the manner in which FIGS. 5 through 42 are positioned adjacent one another;

FIGS. 5 through 42 when positioned as shown in FIG. 4 show in detail the various circuits and the method in which they cooperate to form an exemplary system embodying the present invention, and FIG. 16A is a partial section view taken along line 16A--16A of FIG. 16 showing in greater detail the stepping mechanism of the stepping switch described herein;

FIGS. 5 through 25 including 16A show in detail the equipment at the transmitting station while FIGS. 26 through 42 show in detail the circuits at the receiving station;

FIG. 43 shows a perspective of an exemplary cathode-ray tube embodying the present invention which is suitable for use as a coding device at the transmitting station;

FIGS. 44, 45, 47, 48, 49, 50, 53, and 54 show graphs of voltages and currents at various positions in the system illustrating the mode of operation of the various circuits and the manners in which they cooperate with each other; and

FIGS. 46, 51, and 52 show the manner in which the graphs may be positioned adjacent one another.

GENERAL DESCRIPTION

FIGS. 2 and 3 when arranged as shown in FIG. 1 show in outline form the various component circuits in the manner in which they cooperate to form an exemplary system in accordance with the present invention. FIG. 2 shows the transmitting equipment including the coding apparatus, cipher key generating apparatus, the synchronizing equipment and the keying equipment for combining the output of the cipher key generating equipment and the output of the coding apparatus. FIG. 3 shows the corresponding equipment at the receiving terminal including the receiving synchronizing and controlling equipment, the receiving key generating equipment, the key equipment for again combining the output of the key generator with the received signals to recover the original code signals from the transmitted enciphered signals. The deciphered signals are then decoded and the original communication signals or wave forms recovered. In FIG. 2, 210 represents the source of signal which is usually a microphone for voice signals, but may include any other suitable source of signals including telegraph signals, picture signals, frequency division multiplex signals, facsimile signals, etc. The source of signals 210 is connected to the terminal equipment 211 by means of any suitable type of transmission circuits and paths including telephone open-wire lines, cable circuits, carrier current communication paths, radio paths, toll circuits, etc. The terminal equipment 211 may include various types of switching equipment for establishing communication paths from the source 210 to the terminal equipment in the exemplary system set forth herein. Each of these systems as well as the associated equipment operates in its usual and well-understood manner so that it is not necessary to repeat a description of the operation thereof herein.

The output of the terminal equipment 211 is transmitted through switches 212 and 213 which switches, when set in the position shown in the drawing cause the signaling currents or wave form which is usually a complex wave form to be transmitted from the transmitter 210 through the terminal equipment 211 and switches 212 and 213 to the code and differentiating circuit 214. The coding circuit 214 causes the amplitude of the complex wave form to be represented by a plurality of signal currents of either one or the other of two different signaling conditions. As shown in FIG. 2, five such signaling currents or pulses are employed to represent the amplitude of the output from the terminal equipment. Where desired, the code information may be in effect differentiated so that the pulses will represent not the amplitude of the complex wave, but rather changes in the amplitude of the complex wave. The signaling or current conditions are transmitted from the coder 214 to the transmitting time division system and keyer 215.

With switch 232 set in the position shown, the keyer will ause the applied pulses to be repeated through the transmitter time division system without alteration and in proper time sequence. The timing and synchronizing of the transmitting equipment 215 is controlled by a master oscillator 217 and control oscillator 218 through the synchronous pulse generator 219 and other control equipment as will be described hereinafter. The output pulse code signals are transmitted over the communication path extending to a distant station. The apparatus 221 is arranged to convert the coded signals into high frequency radio signals or other signals suitable for transmission over open-wire lines, coaxial cable circuits, wave guides, ultra-high frequency radio waves and the like. At the receiving station, the signals are received by the radio antenna 322 or over the other type of transmission path employed and transmitted through the receiving circuit 321 which responds to the incoming signals and causes a series of signaling currents of pulses similar to those received from the transmitter time division equipment 215 to be applied to the receiving time division equipment and keyer 315 through the adjustable delay network 309. The receiving time division and keying apparatus 315 is controlled by the control oscillator 318 and the synchronous pulse generator 319.

As shown in the drawings, a separate synchronizing channel 260 extends between the transmitting and receiving stations. It is to be understood, of course, that the synchronizing signals may be transmitted over the main communication path or the signals themselves may be employed for synchronizing purposes at the receiving station. Inasmuch as the various methods of transmitting the synchronizing signals from transmitting station to receiving station and controlling the receiving apparatus at the receiving station are well understood in the prior art, a detailed description of the operation of such equipment has not been included herein.

With the receiving time division circuits 315 operating and with switch 332 in the position shown, the signals output from the receiving equipment 315 are transmitted through and combining an integrator circiut 314 and then applied to the lowpass filter 308 which recovers the original wave form and transmits it through the switch 348 and the terminal equipment 311 to the receiving device 307. The receiving device 307 is arranged to respond to the same type of signals as transmitted by the transmitting device 210. If the system is arranged to transmit pulses representing the amplitude of the complex wave, then the receiving and integrating equipment 314 merely combines the coded pulses to obtain a pulse that has an amplitude represented by the coded pulses. If on the other hand, the coding and differentiating equipment 214 is arranged to transmit coded pulses representing a change in amplitude of the complex wave form from generator 210, then the integrating and combining circuit 314 is arranged to, in effect, integrate or change the received pulses into code groups of pulses again representing the amplitude of the complex wave or signal currents and then regenerate from these coded pulses a complex wave form similar to the wave form transmitted from the signal source 210.

The foregoing description of FIGS. 2 and 3 is for transmission in a single direction from the station shown in FIG. 2 and more specifically to the source of signals 210 to the receiving apparatus 307. If it is necessary or desirable to transmit in the reverse direction it is necessary to duplicate the equipment shown in FIGS. 2 and 3 for transmission in the reverse direction.

The lower portions of FIGS. 2 and 3 show in outline form the various component parts of the key generator employed at the transmitting and receiving stations. FIG. 2 shows the circuits and equipment to encipher the coded signals at the sending station and FIG. 3 shows the circuits and apparatus at the receiving station to decipher and recover the original signals from the enciphered signals transmitted between the two stations. The key generator equipments are shown within the rectangle 233 of FIG. 2 and rectangle 333 of FIG. 3. In general, the key generator comprises a delay line or delay system 234. Delay line 234 is arranged to transmit pulses from the delay device 231 down the line and through the delay apparatus such that a given pulse will arrive at each one of the branch points of connecting terminals at a given instant of time. As shown in the drawings fifty such taps are provided although any suitable number may be employed and different lengths of delay line or delay devices providing different delay times may be connected between each of the leads or connections shown in FIGS. 2 and 3. In addition, any additional number of connections to the delay line may be provided as may be desired. The greater the number of these connections the more diverse becomes the key generator and the harder it is to break the cipher system or signals, i.e., decipher by unauthorized persons signals enciphered under control of key signals from the key generator.

The output of each one of the taps or leads from the delay line is connected to a bank terminal of stepping switch 235. The interconnections between these lines and the terminals of the stepping switch have not been shown in detail in the drawings because these connections will usually be arranged to be readily changed and will be frequently changed when it is desired or necessary to change the enciphering code or system. The stepping switch is arranged to provide five output connections in the delay system at any given instant of time. These output connections are then employed to convey the pulses to a tape stepping switch 236 which tape switch will in effect interchange the connections between the five incoming leads and the five outgoing leads. The connections within the tape switch will be changed at frequent intervals and thus provide a greater degree of secrecy and make the code more complicated and more difficult to break.

The five output leads from the tape switch are combined by a series of devices called "mark space reversers" 237, 238, 240 and 242. These mark space reversers are circuit arrangements similar to keying arrangements included in the transmitting time division and keyer circuits 215. These circuits operate in response to signals of two different conditions applied to their input leads and cause a resulting signal to be applied to the output leads which signal may also comprise either one of two different signaling conditions. For example, if the input signaling conditions are of like kind, that is, either both spacing or both marking, one type of signaling condition, for example marking, is applied to the output leads. If, on the other hand, the input signals are of opposite character, that is, one spacing and the other marking, for example, then the output signal is of the opposite character, that is, spacing under the assumed conditions.

The signals from the first two leads from the tape switch are combined in the mark space reverser 237 and the signals from the next two leads from the tape switch are combined in the above manner by the mark space reverser 238. The output of the mark space reverser 238 is then combined with the signals from the fifth lead by mark space reverser 240. The output signals from the mark space reverser 237 are transmitted through a delay device 239 which in part compensates for the time required for the signals to be transmitted through the pulse lengthener 241. The signals from device 240 are transmitted through a pulse lengthener 241 and then combined with the delayed signals from delay device 239 by means of the mark space reverser 242. The signals from the mark space reverser 242 then comprise the key signals which are later combined with the coded signals to form the output enciphered signals. These key signals, however, are transmitted through two switching devices before being combined with the communication signals. The key signals from the mark space reverser 242 are transmitted through a switching transient silencer circuit 244 which interrupts the output of the key generator during the times the stepping switch 235 and the tape switch 236 are being advanced. In addition, the key signals are also transmitted through a transmitting key lock circuit 250 which is employed in the synchronizing of the keying equipment at both ends of the system.

The key generating equipment 333 at the receiving station is similar to the key generating equipment 233 at the transmitting station. This equipment comprises a delay system 334, stepping switch 335, tape switch 336, mark space reversers 337, 338, 340 ad 342. These devices work in substantially the same manner as those in the transmitting station shown in FIG. 2.

A random signal generator 230 is provided at the transmitting station for supplying pulses to the delay system 234 at the transmitting station. This random signal generator comprises a source of random noise currents preferably having no regularly recurring components. These noise currents are amplified so that pulses of either one or the other of two conditions are supplied from the random signal generator 230 to the delay device 231 and then to the delay system 234. Similar pulses are transmitted through switch 216 when the switch level 216 is operated to engage the terminal 229. Thereafter these pulses are transmitted through the time division multiplex and keyer equipment 215, the transmitting and amplifying equipment 221 over the radio channel from antenna 222 to antenna 322 and then through the terminating equipment 321 and adjustable delay device 309 and then through the receiving time division multiplex and keyer equipment 315 and through switch 316 to terminal 329, and then through switch 316 when it is operated to engage the terminal 329 and then to the random signal regenerator 330 which regenerates similar pulses to those generated by the random signal generator 230. The regenerated pulses are then transmitted through the delay device 331 to the delay system 334. As a result substantially identical pulses are transmitted down the two delay devices or systems 234 and 334. Furthermore, except for the delay of the transmission system from the transmitting station to the receiving station the pulses travel down these two systems in exact synchronism or coincidence when the two systems are properly synchronized.

So long as the same pulses are transmitted down the two delay systems and the connections between the delay systems and the stepping switches are the same at both ends of the system and the stepping switch and the tape switches at both ends of the system are in similar positions substantially the same key signals will be generated by both key generators 233 and 333. In order to insure that the same key signals are generated at each end it is necessary to start the various control and counting and other circuits at the two ends at proper times. In order to accomplish this, various switches and other circuits and apparatus have been provided. The switch 212 is operated to engage contacts 227, switch 213 operated to engage contacts 228, switch 216 operated to engage contact 229 and switch 232 operated to engage contact 251 all at the transmitting station. In addition the switch 332 is operated to engage contact 351, switch 316 operated to engage contact 329 and switch 348 operated to engage contact 349 at the receiving station. When the switches are operated as described above and before the system is fully set into operation, the coding equipment 216 as well as the transmitting equipment 215 is set into operation under control of the synchronizing oscillators 217, 218 and the synchronizing pulse generators 219. Likewise the receiving time division equipment 315 is set into operation and synchronized with the transmitting equipment 215 by means of signals received over the conductor or signaling path 260, control oscillator 318 and the synchronous pulse generator 319. At this time the pulses from the random signal generator will be applied to both the delay systems 234 and 334 in the manner described above. However, no key pulses are transmitted through the key lock circuits 250 and 350. Furthermore, the holding circuit 226 is blocked so that the communication signals from source 210 will not be transmitted over the system.

When the switches have all been set as described above and the transmitting and receiving multiplex apparatus 215 and 315 are properly synchronized, similar pulses are transmitted down the two delay systems 234 and 334. When it is finally desired to set the system into operation, switch 248 is operated to engage contact 249 and switch 247 closed. As a result a pulse or a substantially square wave form from the square wave generator 246 is transmitted through the hybrid coil 225, contact 228 and switch 213 to the coding apparatus 214. The square wave generator is then coded and transmitted over the communication system to the receiving station where it is decoded and reconstructed by the low-pass filter 308 and then applied to the receiving key lock circuit 350. The output of the square wave generator 246 is also applied to the transmitting key lock circuit 250.

These key lock circuits are provided with a plurality of counters which may be set to count any desired number of square waves from the square wave generator. It is essential, of course, that the counting equipment at the transmitting station and the receiving station be set to count the same number of pulses. When these devices have counted the proper number of pulses in accordance with their setting, they will cause the output of the key generator to be applied to the keying equipment in both the transmitting station and the receiving station so that the signals will be enciphered and later deciphered and the original signal is recovered.

In addition, the key lock circuits of each of the stations completes a transmission path through respective key locks from the synchronous pulse generating equipment to the pulse counters 245 and 345. These pulse counters are arranged to cause the stepping switches 235 and 335 to step after a predetermined number of pulses from the synchronous pulse generators 219 and 319, respectively. Similarly, tape switches 236 and 336 step after a predetermined number of pulses from the synchronous pulse generators 219 and 319 have been counted. These switches are initially set in the same position and the pulse counter at the two ends set to cause them to step after the same number of pulses. As a result these switches step at both ends of the system at substantially the same time and thus stay in step and cause the same key signals to be generated at each station. Furthermore, when the stepping switch and tape controlled switches 235 and 236 are actuated, the switching transient silencer is also actuated to prevent key signals from being transmitted from the keyer equipments. The absence of the key signals in turn causes the holding circuit 226 to be actuated so that the transmission path from the source of signals 210 to the coding equipment is interrupted, consequently no signals representing the complex wave form will be transmitted over the transmission circuit at these times.

After the key locks 250 and 350 are actuated at the beginning of communication between the two stations, the key signals of the transmitting station are combined with the coded signals by means of the circuit similar to the circuits of the mark space reversers FIGS. above. Sometimes circuits of this type are called reentrant circuits. When these two signals are combined they form an enciphered signal which is transmitted over the communication path and radio system to a distant receiving station. At the receiving station the enciphered signals are combined with a second set of identical key signals with the result that the original coded signals are recovered and then decoded and combined to reconstruct the complex wave form transmitted from source 210.

After the system has been set into operation as described above, switch 248 is actuated to the position shown so that signals from source 210 which are transmitted through the holding circuit 226 are applied to the coder 214 through the hybrid coil 225. In addition the random noise generator 223 is connected through the high-pass filter 224 and through the hybrid coil 225 to the transmission circuit extended through the coder and differentiator 214.

Noise currents from the random noise generator 223 pass through the high-pass filter 224. This filter is arranged to pass only the frequency components of the noise currents which have frequencies which are above the speech signaling current to be transmitted over the system. At the receiving station the high frequency noise currents are removed by low-pass filter 308 at the receiving station. However, these noise currents pass radio or other communication paths between the two stations and cause different code groups of pulses to be transmitted during pauses in transmission of the communication currents so that signals transmitted over the communication system at no time represent the communication signals or the signals generated by the cipher key generating equipment at the transmitting station. As a result pulses representing either the communication currents by themselves or the cipher key pulses by themselves, are not transmitted over the communication circuit or path. Consequently, a minimum of information useful to unauthorized persons desirous of deciphering the enciphered signals transmitted over the communication path, is transmitted over the system.

In addition to the main signaling path between the transmitting and receiving stations shown in FIGS. 2 and 3 a synchronizing path or channel 260 is shown extending between two stations in FIGS. 2 and 3. This control path or channel may be similar to the other transmission paths between the stations. Furthermore, if it is so desired the synchronizing signals or the control frequency may be transmitted over one or more of the other transmission paths extending between the two stations. Inasmuch as there are numerous types of synchronizing apparatus in the prior art which will operate over the same transmission paths as employed for the transmission of communication signals and since the operation of this type of equipment is well known and understood by persons skilled in the art, it is considered unnecessary to further expand the present disclosure to show details of a typical system of this type. It is understood, of course, that such equipment will cooperate with the various circuits of the present invention and may be provided when it is so desired

Each of the stations is provided with certain control equipment which may be common to all of the circuits terminating at that station or it may be common to a plurality of the circuits terminating thereafter. Of course, this common equipment may be provided for each of the individual circuits if it is so desired as is well understood by persons skilled in the art. However, in the systems shown in FIGS. 2 and 3 the control circuits and equipment are shown at the top of these figures and may be common to all of the channels which terminate at each of the respective stations.

The common equipment at the station of FIG. 2 comprises a control oscillator 218 which may be of any suitable type, as for example, the types described in detail in any one or more of the following U.S. Pat. Nos. 1,476,721, Martin, Dec. 11, 1923; 1,660,389, Matte, Feb. 28, 1928; 1,684,455, Nyquist, Sept. 18, 1928 and 1,740,491, Affel, Dec. 24, 1929.

The output of the control oscillator is coupled to control a synchronous pulse generator 219. The output of this generator extends to the transmitting time division multiplex circuit 215, transmitting key lock circuit 250 and monitoring equipment 220. The synchronous pulse generator may include one or more delay devices. These delay devices as well as the other delay devices shown in the drawing may be any suitable type of delay network as, for example, one or more sections of one or more of the types disclosed in U.S. Pat. No. 1,770,422 granted July 18, 1930 to Nyquist.

Similar common equipment comprising a control oscillator 318 and synchronous pulse generator 319 are provided at the station shown in FIG. 3.

In addition to the control oscillators 218 and 318 at each of the control stations a master oscillator 217 is shown in FIG. 2. This master oscillator may be located at either of the stations of FIG. 2 or 3 and when so located at either of these stations, may replace the control oscillator 218 or 318 at either of these stations. However, the master oscillator is frequently located at some central point and provides a control frequency for the entire nationwide system or for some smaller division of a large system. Typical oscillators and standard frequency systems suitable for use as a master oscillator or source of control frequency are disclosed in U.S. Pat. Nos. 1,788,533, Marrison, Jan. 13, 1931; 1,931,873, Marrison, Oct. 24, 1933; 2,087,326, Marrison, July 20, 1937; 2,163,403, Meacham, June 20, 1939; and 2,275,452, Meacham, Mar. 10, 1942.

All of the patents referred to above are hereby made a part of the present application as if fully included herein.

In the exemplary embodiment of the invention set forth herein a high speed coding tube is employed in coding apparatus 214. The tube is shown in FIGS. 6 and 43. Referring first to FIG. 43 the tube comprises an evacuated envelope 4310 in the form of a cathode-ray tube which may be of metal, glass, or other suitable material including combinations of metal, glass and other suitable material employed in the construction of evacuated electron tubes and devices. The tube is provided with a source of electrons from the cathode 4311 which is heated by a heater supplied by suitable power through transformer 4318 in the usual manner. In addition, beam forming elements 4312 are provided and then connected to suitable sources of accelerating and beam forming potentials from sources 4328 and 4327 which sources are illustrated as batteries in FIG. 43, but may comprise rectifiers, filters, or other suitable power sources.

In the usual electron beam tube the beam forming elements 4312 are arranged to form a small beam of electrons which is focussed to a small spot on a target or screen. These beam forming elements frequently comprise aperture plates and the like and are provided with suitable apertures to form a spot of small dimension.

In accordance with the present invention the beam forming electrodes 4312 of any suitable number and construction are arranged to form a wide sheet or plane of electrons of very small thickness which likewise is focussed upon the target 4317. The beam forming elements 4312 consequently will usually be provided with apertures in the form of slits instead of small holes as in the usual case. These beam forming electrodes will nevertheless function analogous to cylindrical lenses to focus the beam of electrons in a very narrow line across a target 4317. The beam forming members represent both electrostatic and electromagnetic focussing and beam forming elements including electrodes, coils and related elements and apparatus. Also, the beam forming and focussing may include a combination of both types of elements.

The target 4317 is provided with a plurality of series of apertures arranged in columns as shown in FIG. 43. These apertures are arranged to form the desired code which in the exemplary embodiment set forth herein is a five-element code arranged in accordance with a binary numbering system. It will be readily understood by persons skilled in the art that any number of code elements may be employed and they may be arranged in any desired manner to form the code employed for transmitting the signals as will be described hereinafter. In addition an auxiliary column of apertures 4336 is provided in the plate or target 4317 and employed to shift the beam so that it will not rest between the apertures forming in the code as will be described hereinafter. The source of signals to be coded and transmitted is supplied through the transformer 4319 to the deflecting plates 4313 and 4314. These deflecting plates in addition to having the signals to be transmitted applied to them are connected to the proper biasing potential so that they do not interfere with or aid in the focussing of the electrons in a narrow line upon the target 4317. Deflecting plates 4313 and 4314 deflect the beam vertically in accordance with the magnitude of the signals received through the transformer 4319. As a result the vertical position of the line of electrons across the target plate 4317 is controlled by the magnitude of the applied signals.

Certain portions of this electron beam pass through the apertures in plate 4317 and fall upon or are collected by the collecting elements 4321 through 4326, inclusive, positioned behind the various columns of apertures in the aperture target plate 4317. The electrons in falling upon these collecting elements or anodes change their potential as is well understood. It is thus apparent that the potentials of these elements 4321 through 4325, inclusive, at all times represent the magnitude of the incoming signals applied through the transformer 4319 to the deflecting plates 4313 and 4314. As shown in FIG. 43 the input to the deflecting means is balanced to ground while in FIG. 6 the input to the deflecting means is not balanced with respect to ground. Either arrangement may be employed. In other words the output from elements 4321 through 4325 of the tube at all times is a complete binary code representing the instantaneous amplitude of the applied signal or other complex wave form to be transmitted, which in the usual case is a speech wave form. When desired the beam may be deflected in a vertical direction under control of signals to be coded by magnetic deflecting coils and related apparatus or by a combination of both magnetic and electrostatic means in place of the means shown in the drawing.

In order to prevent the beam of electrons from remaining between any two rows of apertures representing two different amplitudes and thus either causing no potential on the output leads or causing potentials in accordance with two different codes to be applied to the output leads and in order to reduce the time required to shift the electron beam from one row of apertures to the next in an additional set of apertures provided in the target plate 4317 and an additional collecting element or electrode 4326 provided behind these apertures. The auxiliary apertures as illustrated in column 4336 are provided between the rows of coded apertures in columns 4331 through 4335, inclusive. Thus, if the beam of electrons tends to fall between two of the rows of coded apertures in response to the applied signals, a portion of the electrons will pass through one of these auxiliary apertures and cause the collecting element or anode 4326 to become more negative due to the electrons received by it. This element is connected to one of an auxiliary set of deflecting plates 4315. As a result the deflecting plate 4315 will become more negative and tend to move the beam downward so that it will no longer rest between two rows of coding apertures. Instead, the beam or the major portion thereof will pass through apertures of the next lower row. If, however, the signal changes sufficiently then the beam will move up to the next row when the signal overcomes the depressing effect of the potential applied to the auxiliary deflecting elements 4315 and 4316. The auxiliary apertures, collecting element, and the auxiliary deflecting element of the tube described above are frequently called quantizing elements because they tend to cause the beam to occupy the discrete positions on the target plate 4317 and thus tend to represent the magnitude of the incoming signal by any one of a plurality of different discrete codes representing a particular discrete amplitude of the incoming signal. In other words the incoming signal is represented by the code output from the tube and is not a continuous function but one having any one of a plurality of separate and distinct amplitudes.

It is of course apparent that the feedback connection from the auxiliary element 4326 to the auxiliary deflecting plates 4315 to 4316 may include any suitable types of amplifier equipment to secure the desired amount of control of the electron beam to insure that the beam always passes through some one row of code apertures in the target plate 4317.

As shown in the drawing, the target plate 4317 extends some distance below the last row of apertures so that so-called blank code will be transmitted when the beam is directed to its lowermost position by the received signals. If the beam should be moved still lower than the normal range of the tube, the same code will still be transmitted because the beam will not pass through any apertures, will not impinge upon any of the collecting elements, but will be completely intercepted by the target plate 4317.

Likewise if the beam is directed by a signal having a greater amplitude than its normal operating range of the tube above the row associated with the uppermost apertures of the plate, the same code will still be transmitted because as shown in the drawing, the upper apertures of each of the columns 4331 through 4335 inclusive have been extended an appreciable distance above the normal position of the last row of code apertures in the plate. Consequently, if the signals should at any time have amplitudes which would temporarily exceed the range coding tube the codes representing the maximum or minimum amplitude would continue to be transmitted instead of some other code. In this manner the noise distortion introduced by overloading the coding tube is greatly reduced or eliminated.

When desired other or additional apertures in the target or aperture plate may be elongated or extended by a greater or lesser amount as may be desired. These additional or other elongated apertures may be positioned near the center of the plate to effect noise impression or they may be placed at other immediate positions for other special purposes including clipping, compression expansion, etc.

When desired the apertures may be made to come progressively larger or progressively smaller as the amplitude of the applied signaling wave is increased. In the first case the applied wave form is compressed so that a larger signal amplitude may be represented by a given number of codes. In the second case a complex wave form is expanded.

The apertures in the aperture or target plate are described herein as being arranged in rows of columns in which the apertures in any row represent a code group of signals.

It is evident that by rotating the tube or the aperture plate and electron gun structure through 90.degree. the rows become columns and the columns rows so that the rows and columns may be interchanged.

In the exemplary embodiment set forth herein an aperture plate is provided in combination with collecting electrodes behind the apertures. It is evident that an equivalent group of properly shaped and proportioned collecting electrodes can be employed when desired.

It is also assumed herein that when the electrons of the electron beam pass through apertures in the aperture plate and fall upon the collecting electrodes behind these apertures they will cause a potential of the collecting electrodes to be reduced.

However, when desired, the collecting electrodes may be designed and arranged to operate as secondary emitters in which case they become more positive when the electron beam passes through an aperture and falls upon these collecting electrodes because each electron from the electron beam will cause a plurality of electrons to be dislodged from the collecting electrode thus leaving it more positive.

Thus, by providing a sheet of electrons which focus the line upon the target plate, a code representing any of the plurality of different discrete amplitudes of the applied signal is always complete and instantaneously available for transmission. It is unnecessary to move the beam across the apertures as in coding tubes in the prior art such as disclosed in the application of Llewellyn Ser. No. 656,485, filed Mar. 22, 1946.

The coding tube is also represented in FIG. 6 by tube 610 in a more schematic form so that the manner in which it is incorporated in transmitting and code modulation circuits may be more readily understood. Here the cathode is represented by 611 which is heated with power from transformer 618 or in any other suitable manner so that it will admit electrons. These electrons are formed and focussed into a sheet or plane of electrons which impinge upon the aperture target 617. This target is represented by the dotted line in FIG. 6, but actually has a form as shown by the target plate 4317 in FIG. 43. The collecting electrodes or anodes behind the target are represented at 621 through 626 in FIG. 6. Here the incoming signals are applied to the deflecting plates 613 and 614. Feedback path from the quantizing collecting element 626 is connected through vacuum tube 640 to the quantizing deflecting plate 615. The other quantizing deflecting plate 616 is connected to tube 642. The tubes 640 and 642 are shown as cathode follower tubes. Tube 640 is employed to respond to a small number of electrons falling upon the collecting element 626 which causes a small drop across the resistor 641. The tube 640 thereupon causes a much larger current to flow through the cathode resistor 620 and accurately control the potential of the deflecting plate 615. In other words, the cathode follower tube is employed as a current amplifier or impedance and changing device which has a high impedance input circuit and thus readily responds to a small number of electrons collected by the collecting element 626. Nevertheless it accurately controls the potential of deflecting plate 615 which may have appreciable capacity and thus a lower impedance.

It is to be understood of course that tube 640 represents an amplifier which may include more than a single stage cathode follower tube as shown in the drawing.

Tube 642 is similarly connected to the other correcting deflecting plate 616. Tube 642, however, has its grid connected to the voltage divider 644. The divider 644 may be adjusted for the purpose of centering or properly adjusting the position of the electron beam in tube 610. In addition tube 642 also tends to compensate for changes in battery potential of the various supply sources employed in the system. Thus, for example, if the anode batteries of the tubes 640 and 642 change, a corresponding change is applied to both quantizing plates 615 and 616 so that this change in battery potential is largely balanced out and does not cause improper operation of the coding tube and does not, in effect, add noise or other spurious currents to the coding apparatus which currents might otherwise appear as noise in the decoded signals.

Novel features of this coding tube disclosed but not claimed herein are claimed in my copending application Ser. No. 37,035 filed July 3, 1948.

The above-described operation of the coding tube 610 is illustrated by the graphs in FIG. 44. 4410 shows a portion of the target similar to 4317 of the coding tube. This target is provided with a plurality of apertures arranged in six vertical columns 4415, 4414, 4413, 4412, 4411 and 4416. The vertical column 4411 comprises the apertures which control the digit in the first digital position or digit of highest denominational order of a corresponding binary number, likewise column 4412 comprises the apertures which control the second digit of the number and so on. The vertical column 4416 represents the apertures for providing auxiliary control of the electron beam within the tube.

It is assumed, for purposes of illustration, that the applied wave has a wave form such as illustrated by graph 4405 in FIG. 44. This graph has been superimposed upon the apertures of the target in such a way that it is assumed that at any time t along the X-axis the electron beam will be at a height on the target shown by the position of the graph 4405 at that time. Thus assuming that at time t1 the beam will be at position 4407, at a later time t2 the beam will be at a position 4408 and at a still later time t3 the beam will be at a position 4409. When the beam is in position 4407 it passes through only the one aperture in column 4411 thus indicating an amplitude of sixteen for the complex wave form at the time t1. The graph 4421 illustrates the potential on the collecting electrode 621 at this time and since the beam passes through an aperture in column 4331 and 4411 it impinges upon this electrode. The electrode will be at its more negative potential as illustrated for time t1 by graph 4421. The beam will not pass through any other apertures in front of any of the other coding electrodes 622 through 625. Consequently these electrodes will be at their more positive potential at time t1 as illustrated by graphs 4422, 4423, 4424 and 4425. At a slightly later interval of time the beam will be depressed due to the applied voltage illustrated by graph 4407 and will pass through an aperture in column 4416 which will cause current to flow and change the potential of the collector electrode 626 which will cause the beam to be immediately further deflected as illustrated by the dotted line 4404. Thus, the beam will then pass through apertures in columns 4412 through 4415, inclusive, and will not pass through an aperture in column 4411; as a result the potential of the collecting electrode 621 rises to a more positive value as illustrated by graph 4421 while the remaining coding electrodes 622 through 625, inclusive, will assume a more negative potential value due to the fact that electrons from the beam pass through apertures in front of these collecting electrodes and reduce their potentials. The voltages of these other electrodes at this time are represented by graphs 4422 through 4425. At each succeeding instant of time, the electron beam is deflected as indicated by graph 4405 and will pass through various ones of the apertures in the various columns. At time t2, for example, without the quantizing control apertures 4336 and 4416 the beam will be between the rows of apertures representing amplitudes of seven and eight. At this time t 2 the beam will pass through the aperture in column 4416 and thus cause the collecting electrode 624 to assume a more negative potential which in turn will depress the beam so that it will pass through the apertures representing an amplitude of seven. As a result the voltage of the electrodes 613, 614 and 615 will be negative and the voltages of all of the other collecting electrodes are at their more positive potential, as illustrated by graphs 4421 through 4425 at the time t2.

It is thus evident that at any time t, the potentials on the output electrodes represent in coded form the displacement of the electron beam and thus the magnitude of the complex wave form applied to the system described herein.

As will be described hereinafter the approximate times t1, t2 and t3 have been selected as the times at which pulses representing the amplitude of the complex wave form are to be transmitted over the multiplex system.

As shown in the drawings, a monitoring circuit 220 is provided at the transmitting station. This monitoring circuit enables the attendant to observe the operation of the coding circuits to determine if they are operating properly. The monitoring circuit may comprise receiving multiplex and pulse code demodulation and decoding equipment. This monitoring circuit may comprise substantially all of the apparatus at the receiving station as described hereinafter. The monitoring circuit operates in the manner well understood in the art or in accordance with the receiving equipment and circuits described herein. Consequently, there is no need to repeat the description of the operation of this equipment at this time.

A detailed description of an exemplary system embodying the present invention may be more readily understood with reference to FIGS. 6 to 62, inclusive, and arranged adjacent one another as shown in FIG. 4.

COMMON EQUIPMENT

In order to better understand the operation of the system the common equipment shown on the top of FIGS. 2 and 3 in diagrammatic form will be described first.

FIG. 5 illustrates a master oscillator 510 and the secondary oscillator 512. If the master oscillator 510 is located at the transmitting station the details of which are illustrated in FIG. 3, local oscillator 512 may be dispensed with. However, in case the master oscillator 510 is located at some other station or is a master frequency standard for a large number of stations, systems, or for the entire country, both oscillator 510 and the local oscillator 512 will usually be employed. Master oscillator 510 may be of any suitable type such as the type disclosed in the above-identified Meacham or Marrison patents. The local oscillator 512 will then incorporate control apparatus for maintaining its frequency in synchronism with the frequency from the master oscillator 510 similar to the equipment described in detail in the above-identified patents. Oscillator 512 is connected over a synchronizing line 511 which is shown in FIG. 5 as a coaxial line and extends to receiving station shown in FIGS. 26 through 42, inclusive. The coaxial line 511 terminates at the receiving station in a local oscillator 2612 which is similar to the oscillator 512. While the synchronizing line 511 is shown as a coaxial line, it is to be understood that any suitable type of transmission path may be employed which is capable of transmitting the synchronizing frequency employed.

SYNCHRONOUS PULSE GENERATOR

The local oscillator 512 or the master oscillator 510 is connected to a multivibrator circuit comprising tube 513. The multivibrator circuit 513 operates to generate square waves which usually have the same frequency as received from oscillator 512 or 510. However the frequency of operation of multivibrator 513 may be different from the frequency of the controlling oscillator. In addition the frequencies of operation of the oscillators 510, 512 and 2612 will usually be the same but may be different when desired. Multivibrator circuits are well known in the art. Typical multivibrator circuits for use in the present system are described in U.S. Pat. Nos. 1,744,935 granted to Van der Pol Jan. 28, 1930 and 2,022,969 granted to Meacham on Dec. 3, 1935, and in an article by Hull and Clapp published in the Proceedings of the Institute of Radio Engineers for February 1929, pages 252 to 271. See also section 4-9 "Multivibrator" on page 182 of Ultra-High-Frequency Techniques by Brainerd, Koehler, Reich and Woodruff. The output of the multivibrator 513 is coupled through a condenser 514 and a resistance 515 to amplifier tube 516.

Condenser 514 is made variable so that it, together with resistance 515 may be employed to control the length of the synchronizing pulses derived from multivibrator circuit 513. If the time constant of condenser 514 and resistance 515 is large, the output pulse will be relatively long, whereas if the time constant of condenser 514 and resistance 515 is small the output pulse will be short. In a typical example of the present system the values of condenser 514 and resistance 515 were selected to produce an output pulse of approximately two microseconds duration.

Condenser 514 and resistance 515 are coupled to the control grid of amplifier tube 516. The output of the amplifier tube 516 is in turn coupled to tubes 517, 518, 519, 520 and 521. Tubes 516, 517 and 518 are amplifier tubes which are overloaded by the magnitude of the pulse applied to them so that these tubes tend to limit the magnitude of the pulse repeated through them and at the same time tend to make it square in wave shape. Amplifiers of this type are sometimes called "limiters" and at other times "clipping" amplifiers because they limit, clip off or suppress the top portion of the waves applied to them. A single stage "limiter" is shown in FIGS. 8-6 on page 282 and described on page 283 of Ultra-High-Frequency Techniques by Brainerd, Koehler, Reich and Woodruff. First published July 1942 by D. Van Nostrand Company, Incorporated.

The output of tube 518 is coupled to tubes 519, 520, and tube 521 is coupled to tube 520 which tubes prevent improper interaction between the various utilization circuits and supply sufficient power for the output pulses of the circuit so that they may be employed to control the other circuits of the system. The output circuit of tube 519 is arranged to supply both positive and negative pulses. Negative pulses are obtained from the plate of tube 519, while positive pulses are obtained from its cathode as shown in FIG. 5.

In case a large number of circuits are supplied from pulse generator shown in FIG. 5, additional output stages may be connected in parallel with tube 519, i.e., may have their input circuits connected in parallel with the input circuit of tube 519 or may be driven from this tube as is well understood and frequently employed.

The negative pulses from the plate of tube 519 pass through a delay network 560 where they are delayed slightly in time with respect to the synchronous pulses. The purpose of this delay will be explained hereinafter. Delay network 560 will be of any suitable type employing reactive elements in a manner well understood in the art and pointed out above. The undelayed output of the pulse generator shown in FIG. 5 is diagrammatically indicated by the lines 4501 of FIG. 45 for the positive pulses. The negative output pules of course will occur at substantially the same time. Under the assumed condition the synchronous pulse generator circuit generates pulses at the rate of 10,000 per second so the pulses occur at intervals of 100 microseconds.

CODE ELEMENT TIMING CIRCUIT

The output from the anode of tube 519 is connected through the delay device 560 to code element timing circuit comprising tubes 803, 822, 823, 824, 901 and 902. The tube 803 is employed to drive the left-hand section of tube 822, which tube in turn is employed to shock-excite the resonant circuit comprising condenser 825 and inductance 826 connected in parallel in the cathode circuit of the left-hand section of tube 822. The bias conditions applied to the left-hand section of tube 822 are such that the tube is blocked or non-conducting at all times except when the positive pulse from tube 803 is applied to its grid. At these times the left-hand section of tube 822 forms a low impedance path for supplying current and energy to the oscillating circuit connected in its cathode circuit. At all other times the anode-cathode circuit of tube 822 is of such a high impedance that it does not materially affect the oscillations of the resonant circuit comprising elements 825 and 826. The application of a positive pulse to the grid of tube 822 thus sets the resonant circuit described above into oscillation. The wave form of such oscillations is shown by curve 4502 in FIG. 45.

As shown by curve 4502 one suitable type of adjustment for the resonant circuit is such that substantially five complete oscillations take place between the delayed positive synchronizing pulses 4503 applied to the grid of the left-hand section of tube 822.

In other words, one cycle or oscillation is generated between the synchronizing pulse for each code pulse of each group of code pulses. If six or some other number of pulses are required to represent the various amplitudes of each sample of the complex wave then the tuning of the resonant circuit comprising condenser 825 and inductance 826 would be varied to generate six or the required number of cycles or oscillations between synchronizing pulses.

As shown by curve 4502 slightly more than five complete oscillations of the resonant circuit take place but the synchronizing pulse causes the circuit to start oscillating from substantially the same point and with the same phase each time it is received. By supplying energy to the oscillating circuit when the current through the coil is small and by utilizing the low impedance of the cathode circuit, transients are small and quickly damped out. Transients do not, therefore, materially affect the frequency or amplitude of the oscillations and at the same time the oscillations are maintained in proper phase.

The cathode of the left-hand section of tube 822 is connected to the grid of the right-hand section of this tube. The output impedance of the right-hand section comprises a cathode resistor 827 which is of such a value that the right-hand section of tube 822 acts as a so-called "cathode follower" and thus presents an extremely high impedance to the resonant circuit comprising elements 825 and 826. Consequently, the operation of the right-hand section of tube 822 does not materially alter or interfere with the operation of the resonant circuit. Such properties and operation of "cathode followers" are well known to persons skilled in the art. (See "The Cathode Follower" by C. E. Lockhart, Parts I, II and III, published in Electronic Engineering, December 1942, February 1943 and June 1943, respectively.)

The cathode of right-hand section of tube 822 is coupled through a resistance and capacity network to the grid of tube 823. Capacity 828 and resistance 829 are employed in the coupling circuit in order to properly control the wave shape of the pulses transmitted to and repeated by the tube 803. Resistances 814 and 829 together with the position of potentiometer 818 control or determine the bias of the grid of tube 823. Condenser 828 is connected across resistance 829 to compensate for the effect of the input capacitance of tube 823, thus causing the potential of the grid of tube 823 to rise substantially as fast as the applied potential, i.e., the potential of the cathode of the right-hand section of tube 822. The optimum value of condenser 828 is the value of the input capacitance of tube 822 multiplied by the ratio of resistance 829 to resistance 827. It should be noted that the potentiometer 818 is connected between the negative source of bias potential or battery and ground.

The output of tube 823 is similarly connected to tube 824 and the output of this tube in turn, connected to tube 901. Tubes 823 and 824 are adjusted to operate as overload amplifiers so that they will limit the amplitude of the output pulse and at the same time cause these pulses to approach a square wave form. Tube 901 is a power tube for supplying sufficient output power to operate the other circuits as will be described hereinafter. In this case as in the case of the output the pulse generator, sufficient additional output tubes may be provided in parallel with or supplied by tube 824 to provide the necessary output currents and voltages as well as to isolate the various different circuits one from another, as may be required.

The amplifier tubes 822, 823 and 824 have their circuits and bias potentials so adjusted that a wave form approaching that illustrated by curve or broken line 4504 appears in the output from the tube 824. Both the positive and negative portions of this wave form as shown in the drawing are substantially of the same duration. Persons skilled in the art will at once realize that it is not necessary that both of these portions of the wave be of equal or substantially equal duration but may and usually will be of different duration to secure optimum operation. Furthermore, these waves are shown to be rectangular in form, as are other waves in the drawing. In practice, the waves are rounded to a greater or lesser extent. Inasmuch as typical actual wave forms approach the wave forms shown in the drawing and would not further aid in an appreciable manner the understanding of this invention the actual waves are represented by the forms shown in the drawing which are much easier to draw and adequately represent the operation of the system.

CONTINUOUS CODING

Assume for purposes of illustration that the various switches shown in the drawing are operated to the positions shown.

When the switches are so operated the exemplary system set forth herein is arranged to respond to and transmit complex wave forms such as voice frequency waves including speech, music and the like or any other suitable types of complex wave forms having frequency components having frequencies within the same frequency range. Such other wave forms may represent telegraph signals, picture currents and so forth. The complex wave is then translated into code groups of signals which signals are employed to generate pulses representing the instantaneous amplitude of the complex waves at each of a plurality of rapidly recurring instants of time. These pulses are then transmitted over a transmission system which may take a form of a radio path including the highest radio frequencies which when transmitted exhibit many properties of light beams. The transmission path may also include coaxial cables, wave guides, and other suitable transmission circuits, apparatus and media capable of transmitting the necessary and desired frequency range.

The signals as received at the receiving terminal are then decoded and a wave form similar to the original complex wave form will be constructed and transmitted to terminal equipment.

FIG. 6 shows a signal source 601 which corresponds to source 210 of FIG. 2. As shown in FIG. 6 source 601 is represented by a microphone. However, any suitable type of signal source may be employed including telegraph and picture apparatus.

The source 601 is connected to the terminal equipment 602 which terminal equipment may and usually will include one or more of the following types of equipment such as transmission paths, manual or automatic switching equipment, toll lines, carrier current circuits, radio circuits, amplifiers, gain regulators, coaxial lines, wave guides, repeaters, interconnecting equipment and the like.

This equipment operates in its usual manner as is well understood in the prior art so that details of its operation need not be repeated here. This equipment is employed to extend the transmission or communication path from source 601 to the exemplary transmission system described herein in detail embodying the present invention.

From the terminal equipment 602, the signals are transmitted through switch 603 to terminal 604 when switch 603 is operated to positions shown in the drawing. The signals are then transmitted through switch 607 from terminal 608 to the deflecting plate 613 of the coding tube 610. As a result the electron beam in this tube is caused to move in a vertical direction under control of received signals. Due to the action of the quantizing column apertures 626, quantizing deflecting plates 615 and 616 as well as the repeater represented by tube 640, the beam is moved in discrete steps so electrons of the beam fall upon the collecting elements 621 through 625, inclusive. The particular ones of these elements upon which the electrons fall is determined in part by the apertures or codes in the plate 617 and also by the magnitude of the received signals.

As a result, as pointed out hereinbefore, the elements 621 through 625, inclusive, have at substantially all times potentials applied to them which represent the amplitude of a complex wave form by means of a chosen code.

As shown in FIGS. 6 and 43, the coding tube is arranged to represent the instantaneous amplitudes of complex wave forms by means of a five-element binary code. It is to be understood, however, that any other type of binary code or other type of code may be employed. The greater the number of elements of the code employed the greater the number of discrete amplitudes of the incoming signal which may be represented by the code.

The aperture plate 617 of the tube may be formed as shown by the aperture plate 4317 in which the codes representing binary numbers are employed to represent a various successive amplitude of a complex signal wave. Any other suitable code may be employed such as the code disclosed in the patent application of Gray, Ser. No. 785,697 filed Nov. 13, 1947.

As shown in the exemplary embodiment set forth herein, the five output leads are connected to a synchronously operated multiplex distributing and transmission system. It is, of course, well understood that the output from each of these leads may be transmitted over a separate communication path extending to the receiving station and there employed to regenerate a complex wave form similar to that received from the terminal equipment 602. However, by means of time division multiplex systems the output of each one of these leads or terminals may be transmitted in sequence over a time division multiplex system at rapidly recurring instants of time. As is well understood, the recurrence rate should be somewhat greater than twice the highest frequency component of the signals received from the terminal equipment 602 which is necessary or desired to transmit to the distant terminal of the system.

The transmitting multiplex equipment which successively transmits signals representing the output from each of the code element electrodes of tube 610 is shown in the lower half of FIG. 8 and in FIG. 11. Each row of tubes starting with tubes 811, 821, 831 and 851 of these figures is employed to transmit signals from one of the code element electrodes such as 621. The next row of tubes 1112, 1122, 1132 and 1152 is employed to transmit signals from another one of the electrodes such as 622 of tube 610, for example.

The distributor equipment shown in FIG. 8 and 11 is driven by pulses from the synchronous pulse generator shown in FIG. 5 and pulses from the code element time generator equipment shown in the upper portion of FIG. 8. A positive pulse is applied to lead 801 from the synchronous generator in FIG. 5 for each complete code combination. A negative pulse is obtained from lead 802 for each of the code elements of a complete code combination. Thus when the system arranged to transmit five-element binary permutation code signals five negative pulses are obtained from lead 802 from tube 901 for each pulse received from the synchronous pulse generating equipment over lead 801. These negative pulses are obtained by the condenser resistance combination 804 which has a low or short time constant so that the square wave is in effect differentiated and a negative pulse applied to the grids of tubes 840 and 850 each time the square wave 4504 changes from a positive value to a more negative value. The positive pulses obtained when the square wave changes in the other direction are largely suppressed by the bias conditions applied to tubes 840 and 850. The negative pulses are represented by lines 4505 and the corresponding positive pulses obtained from tubes 840 and 850 are represented by lines 4506. Furthermore, as shown in FIG. 45, the first negative pulse obtained from lead 802 is slightly in advance of the time a delayed positive pulse is applied to lead 801. The negative pulses applied to the grids of tubes 840 and 850 are repeated by these tubes 840 and 850, operating in parallel, as a positive pulse which pulse is applied to a control element of each of the tubes 851, 1152, 1153, 1154 and 1155. Tubes 851, 1152 through 1155, inclusive, operate as cathode follower tubes and cause the condensers individual to their cathode circuits 841, 1142, 1143, 1144, 1145 to become charged during the application of the positive pulse to control elements of the respective tubes. Each of these condensers becomes charged to substantially the same voltage which is a function of or substantially equivalent to the voltage or magnitude of the positive pulse applied to the control elements of tubes 851, 1152 through 1155, inclusive.

As pointed out above, the positive pulse is applied to lead 801 after the negative pulses obtained from lead 802 have terminated. The exact times at which these pulses are applied to these leads may be controlled by delay times of the delay devices 550 and 560. The pulses applied to lead 801 from the synchronous pulse generator shown in FIG. 5 are transmitted through delay device 550 and thus the delay introduced by this device controls the exact time of application of the pulses to lead 801. Pulses applied to the code element timing circuit shown in the upper portion of FIG. 8 are transmitted through the delay device 560; thus by adjusting the delay of this device the exact timing of the pulses obtained from lead 802 may be controlled.

The pulses as applied to lead 801 are delayed in time as well as in effect differentiated by the inductance and condenser circuit 861. As shown by lines 4507 these synchronizing pulses are delayed by this combination so that the grid of tube 831 will be positive after the short positive pulses 4506 applied to the grids of tubes 851, 1152 through 1155, inclusive, have terminated. The pulses applied to the control elements of the above tubes as its wave form may be controlled by the condenser resistance network 804 and by condenser 805 and the resistance 806. These networks have a short time constant. That is, the product of resistance and capacity of these networks is small so that they in effect differentiate or transmit only a very short pulse through them upon the application of a pulse or square wave to them from the previous circuit.

The application of a positive pulse to the control element of tube 831 after positive pulse applied to control element of tube 851 is terminated causes the upper terminal of condenser 841 to become discharged. The upper terminal of condenser 841 is connected to the control element of tube 821. Likewise, upper terminals of condensers 1142 through 1145, inclusive, are connected to the control elements of the respective tubes 1122 through 1125, inclusive. Thus after the application of a positive potential to the control element of tube 831 the control element of tube 821 has a relatively low voltage applied to it whereas the corresponding control elements of tubes 1122, 1123, 1124 and 1125 have a relatively high positive voltage applied to them from the corresponding condensers 1142, 1143, 1144 and 1145. The anode circuits of tubes 821 and 1122 through 1125, inclusive, are coupled to one of the control elements, frequently called the screen or screen grid, of tubes 811, 1112 through 1115, inclusive. These tubes are biased and are arranged so that they will pass substantially no anode current unless the screens of these tubes are at a relatively high positive potential. The coupling condensers between the anodes of the respective tubes 821 or 1122 through 1125 and the screens of tubes 811, 1112 through 1115, inclusive, as well as the screen resistors have a relatively long time constant; that is, the product of their capacity and resistance is relatively large compared to the duration of the signals. As a result the voltage or potential of the screen of tubes 811, 1112 through 1115, follows the potential of the anodes of the respective tubes 821, 1123 through 1125. When a positive voltage is applied to the control elements of tubes 1123 through 1125, inclusive, substantial current flows in the anode-cathode circuit of these tubes and produces a large voltage drop across the anode resistance with the result that relatively low voltage is applied to the screens of tubes 1112 through 1115, inclusive. Under these circumstances a bias voltage applied to the other elements of the tubes 1112 through 1115 is such that substantially no current will flow in their output circuits independently of the potential applied to other of the control grids such as the inner grid frequently called the control grid. However, inasmuch as a relatively low voltage is applied to the control element of tube 821 substantially no or much less current flows in the anode-cathode circuit of this tube with the result that this anode is a relatively high positive voltage. Consequently, voltage of the screen grid of tube 811 is at a sufficiently high positive voltage so that current may flow in the anode-cathode circuit of this tube depending upon the voltage of the inner or number one grid.

The application of the next pulse from the output circuits of tubes 840 and 850 to the control grids of tubes 851 and 1152 through 1155, inclusive, causes condenser 841 to be charged. In addition, condensers 1142 through 1145 are again charged to the full positive potential as controlled by the magnitude of pulses applied to the control grids of the corresponding tubes. In the case of condensers 1142 through 1145, however, the charge supplied to these condensers at this time compensates for loss due to leakage currents because the condensers are not otherwise discharged.

Upon the application of positive potential to the upper terminal of condenser 841, at this time, current again starts to flow through the anode-cathode circuit of tube 821 thus causing the voltage at the anode of this tube to fall to a relatively low value which in turn causes the screen of tube 811 to have its voltage reduced so that current can no longer flow in the anode-cathode circuit of tube 811, independently of the voltage of the control grid of this tube. That is, even though the control grid is positive, substantially no current flows in the output circuit of tube 811 at this time. The anode-cathode current of tube 821 flows through the cathode resistor of this tube as well as the anode resistor with the result that upon the initiation of a discharge through the tube 821 due to the charging of condenser 841, as described above, the voltage or potential of the cathode of tube 821 is increased.

The cathode of tube 821 is coupled through the coupling network 1162 comprising an inductance and condenser to a control element of tube 1132. This network is similar to the network 861 and causes a delayed pulse of short duration represented at 4508 of FIG. 45 to be applied to the control element of tube 1132. This delayed pulse 4508 does not terminate until after the positive pulse applied to the control elements of tubes 851 and 1152 through 1155, inclusive, is terminated. As a result the upper terminal of condenser 1142 will be discharged and increase upper current following through tube 1132. At this time tube 1122 will cause a voltage applied to the screen grid of tube 1112 to increase so that current may now flow in the anode-cathode circuit of tube 1113 under the control of the voltage applied to other control elements of tube 1112. At this time, however, the other condensers 841, 1143 through 1145, are substantially fully charged so that the screen grids of tubes 811 and 1113 through 1115, inclusive, are at a low voltage with the result that these tubes are unable to pass current in their anode-cathode circuits even though the control grid of these tubes becomes so positive as that of tube 1112 which tube will conduct current if its control grid has a positive signaling voltage applied to it at this time.

The circuits then stay in the above-described condition until another pulse is repeated by tubes 840 and 850 at which time the screen of tube 1112 again becomes more negative and the voltage applied to the screen of tube 1113 becomes sufficiently positive so that this tube will conduct anode-cathode current under control of another grid or control element thereof.

The times during which the tubes 811 and 1112 through 1115 are conditioned to conduct by having the voltage of their screen grids raised to the proper positive value is illustrated by graph 4509. The line 4511 shows the time tube 811 is conditioned to conduct, the line 4512 shows the time tube 1112 is conditioned to conduct, etc.

It is thus evident that the tubes 811, 1112, 1113, 1114 and 1115 are conditioned one after another in sequence to conduct current in their anode-cathode circuits under control of voltage applied to some other control element which is the control grid. It is also apparent that only one of these tubes may conduct current in any one given instant of time.

Each of the code element electrodes or collectors 621 through 625 of tube 610 controls the voltage applied to the control grid of the respective tubes 811, 1112 through 1115, inclusive. The path from each of the collector electrodes of tube 611 to the corresponding distributor gate tube includes repeating tubes and a delay network. For example, electrode 621 is connected to the control element of the repeating tube 711. Tube 711 is shown as a cathode-follower type of tube and is intended to represent generalized amplifier which may include voltage gain as well as the impedance transforming properties of the cathode-follower tubes actually shown. The cathode-follower tube 711 is connected to the delay line 721 and the output of the delay line is connected to the input circuit of the repeating and amplifying tube 761. The output of tube 761 is connected to the input circuit or element of the cathode-follower tube 771. The output of tube 771 is connected through switch 741 when it engages the terminal 747 as shown in the drawing to the control grid of tube 811 through suitable coupling network. The coupling network in this case includes a direct-current path and is arranged so that the voltage of the control grid of tube 811 has at all times substantially the same wave form as the wave form of the voltage at the output terminal of the delay line 721 and at the output of tube 771.

The collecting code element or electrode 622 of tube 610 is similarly connected through repeating tube 712, delay line 722, tubes 762 and 772, and switch 742 to a control grid of tube 1112. Likewise, each of the succeeding output elements of tube 610 is connected through similar repeating, delay, and switching apparatus to a control grid or element of the succeeding distributor tubes of FIG. 11.

The code elements or electrodes 611 through 615, as shown in the drawing, control the voltage or potential of the respective multiplex distributor gate tubes 811, 1112, 1113, 1114 and 1115. These connections have been so shown so that the operation of the system may be more readily understood. When desired the various code electrodes or elements of the coding tube 610 may be connected to control the various multiplex distributor gate tubes in any order or disorder that may be desired. Of course the connections at the receiving gate tubes would have to be changed in a corresponding manner.

As described above, the potentials applied to the code elements 621 through 625 of tube 610 change substantially simultaneously in response to the changes in amplitude of the applied signal wave. However, the distributor tubes 811 and 1112 through 1115 are energized successively as described above so that pulses representing the potential conditions on the code elements 621 to 625, inclusive, are sent in succession.

In order to prevent pulses which are transmitted from tubes 811 and 1112 through 1115, inclusive, from representing different code groups of pulses due to the fact that the potentials on the code elements 621 through 625 change during the time tubes 811, 1112 through 1115 are transmitting a series of pulse delay lines 721, 722, 723, 1024 and 1025 are connected between the respective code element electrodes 621 through 625 and tubes 811 and 1112 through 1115. The delay of the delay device 721 is provided to permit such initial delay as may be desired and compensate for other delays which may be encounterd in the system. The delay device 722 is arranged to provide a delay equal to the delay of delay device 721 plus the time interval between transmitted pulses, that is, the time interval between the energization of successive tubes 811, 1112, 1113, etc. The delay device 723 is provided with the delay equal to the delay of delay line 721 plus twice the interval between transmitted pulses. Simiarly, delay device 1024 is provided with a delay time equal to the delay of the delay line 721 plus three times the interval between pulses. Delay device 1025 is provided with a delay substantially equal to the delay of delay device 721 plus the time between the transmission of four successive pulses.

The delay devices 721, 722, 723, 1024 and 1025 may be of any suitable type such as transmission lines or sections, artificial lines or sections, electronic delay devices such as, for example, the type disclosed in U.S. Pat. No. 2,245,364 granted to Reisz et al on June 10, 1941, or they may be of the type employing supersonic waves such as disclosed in U.S. Pat. Nos. 1,775,775 granted to Nyquist Sept. 16, 1930 and 2,263,902 granted to Percival Nov. 25, 1941. The disclosures of all of the above-identified patents are hereby made a part of the present application as if fully set forth herein.

These delay lines may also be of the type described in an article entitled "Video Delay Lines" by Blewett and Rubel published in the Proceedings of the Institute of Radio Engineers for Dec. 1947, Vol. 35, No. 12, page 1580 through page 1584. The disclosure of the above-identified article is also hereby incorporated herein by reference to the same extent as if fully set forth.

Inasmuch as these delay devices are operated in the usual manner in cooperating with the other elements of the patented system and inasmuch as the operation of all such devices is understood in the prior art, their operation will not be described in further detail herein.

By providing these delay lines or devices with delay intervals such as described above, the series of pulses transmitted by the respective tubes 811 and 1112 through 1115 represent the potential conditions simultaneously applied to the code element electrodes 621 through 625, inclusive. Thus, except for the infrequent case wherein the potentials on code elements 621 through 625 change at substantially the exact time that these potentials will be applied in succession to the distributor tubes 811, 1112, 1113, etc., the delay networks change the pulses or voltage conditions simultaneously applied to the electrodes 621 through 625 into a series of voltage conditions occurring in sequence and applied to the control grids of other control elements of tubes 811 and 1112 through 1115, inclusive.

The outputs of anodes of the distributor tubes 811, 1112, 1113, 1114 and 1115 are all connected together and provided with a common anode resistor or impedance 1118.

When current flows in the output circuit of any one of the distributor tubes 811 and 1112 through 1115, inclusive, current also flows through the common output impedance 1118 and produces a voltage drop across this impedance. This voltage drop is applied as a negative pulse to the control element of tube 1220 and thus causes the cathode of this tube and the cathode of tube 1221 to become more negative. The control element of tube 1221 is coupled through the coupling network comprising condenser 1224 and resistor 1225 to the output of the code element timing circuit which is a wave form substantially as illustrated by graph 4504. The time constant of this coupling network is short so that the wave form illustrated by graph 4504 is in effect differentiated when applied to the grid of tube 1221. The bias applied to the control element of tube 1221 through resistor 1225 is such that the tube is normally non-conducting. When the output wave form in the code element timing circuit changes from its more positive value to its more negative value a negative pulse is applied to the control element of tube 1221. This negative pulse, however, merely tends to further cut the tube off and inasmuch as it is biased beyond cut-off, this negative pulse produces substantially no effect.

However, when the output from the code element beam circuits changes from its more negative value to its more positive value a positive pulse is applied through coupling condenser 1224 and allows tube 1221 to conduct under control of the potential applied to the control element of tube 1220. A pulse of short duration only is applied to the control element of tube 1221 due to the short time constant of condenser 1224 and the biasing resistor 1225. If the control element of tube 1220 is negative at this time due to a negative pulse received from one of the distributor tubes 811 or 1112 through 1115, current will flow in the output circuit of tube 1221 at this time. The negative pulse flows in the output circuit of this tube which pulse is amplified and repeated as a positive pulse by tube 1222. Tube 1223 acts as an output tube and causes a positive pulse to be applied through terminal 1202 and switch arm 1201 and radio transmitter 1204 and antenna 1205.

If, however, the voltage applied to the control element of tube 1220 is more positive at the time positive pulse is applied to the control element of tube 1221 in the manner described above, substantially no current flow in the output circuit of this tube. Consequently, the pulse of opposite character, that is, a spacing pulse, or a pulse of no current is transmitted to the radio transmitting equipment for transmission to the distant receiver.

The above-described operation of the transmission of the pulses to the radio system under the assumed conditions is illustrated by the graphs in FIGS. 44 and 45.

As described above, the potential of the coding element 621 at tube 610 is illustrated by graph 4421 and is negative at the time t1 because the beam passes through an aperture in front of the code element 621 allowing electrons to fall upon the electrode 621. This negative potential condition is repeated in tube 711 as a negative voltage which is transmitted down the delay line 721 and then repeated by tube 761 as a positive pulse. The tube 771 then repeats the positive pulse and applies it to the control element of tube 811 causing this tube to conduct current when it is rendered active. This in turn causes a negative potential in the output of the distributor which potential is then repeated as a positive pulse to the radio circuits by tubes 1220, 1221, 1222 and 1223 in the manner described above. Graph 4521 illustrates the potential applied to the control element of tube 811. This graph is similar to the graph 4421 except that it is inverted and delayed due to the delay introduced by the delay device 711. The shaded portion 4511 represents the time that the screen grid of tube 811 is rendered positive so that this tube will conduct and cause a negative voltage in the output circuit as illustrated by graph 4530. Graph 4531 represents the positive voltage applied to the control element of tube 1221 which in turn causes a positive pulse represented by graph 4532 to be applied to the radio transmitter. Graph 4522 represents the voltage applied to the control element of tube 1112 which is similar to graph 4422 except that it has been delayed by an amount of the delay in graph 4521 plus an amount equal to the time assigned to one pulse interval, that is, the time one step of the multiplex distributing equipment. Graph 4522 is likewise reversed in phase due to the operation of the repeating tube 752 similar to the operation of tube 761 described above. Likewise, the rectangle 4512 represents the time at which the screen of tube 1112 is rendered positive so that the tube is conditioned to conduct at this time. However, inasmuch as the control grid of tube 1112 is more negative no current flows in the output circuit of this tube and as a result, a negative pulse is not applied to the control element of tube 1220 so no positive pulse, i.e., no marking pulse, is transmitted to the radio transmitter at this time. Each of the succeeding graphs 4523, 4524 and 4525 is delayed by a greater delay interval so that the potential applied to the control grid of the respective distributor tubes 1113 through 1115 as well as that applied to tubes 811 and 1112 as described above at the time a positive pulse 4531 is applied to the control element of tube 1221 is controlled by or is a function of the potentials on the output electrodes 621 through 625 of the coding tube at the time t1. Thus, the pulses transmitted to the radio system as illustrated by graph 4532 represent the potential conditions of the electrodes 621 through 625 at the time t1 even though the various pulses are transmitted at progressively greater time intervals after time t1.

A second series of pulses corresponding to time t2 is also shown in the right-hand portion of the graphs of FIG. 45. The operation of the circuits is substantially as described above. It is noted that the potential conditions applied to the control elements of the gate tubes 811 and 1112 through 1115 may change time during the time tubes are rendered active by a positive voltage applied to their screens in the manner described above. However, so long as the voltage is not changed at the time pulses 4531 are applied to the control element of tube 1221 proper signals are transmitted as illustrated in the graphs.

By making the pulses 4531 applied to the control grid of tube 1221 of short duration the probability of the potentials applied to the control grids of tubes 811 and 1112 and 1115 changing at the time the pulses 4531 are applied to the control element of tube 1221 is greatly reduced.

SAMPLING THE APPLIED SIGNALING WAVE

If it is desired to prevent the potential conditions from the code element electrodes of tube 610 from changing at a time such that the codes representing the instantaneous amplitudes will be mutilated, that is, several potential conditions transmitted first in one code and then the successive pulses controlled by the potential conditions of a subsequent code, sampling circuits, storing circuits, clamping circuits and the like or combinations of these circuits may be employed, either connected between the electrodes 621 through 625 of tube 610 and tubes 711, 712, 713, 814 and 815 or similar circuits and elements may be connected ahead of the signal control and deflecting plates 615 and 614 of tube 610.

Such an arrangement is shown in FIG. 6 and comprises tubes 651, 652, 653 and 655 together with the storage condenser 654.

When it is desired to employ this sampling equipment, switch 603 is operated to the position where it engages contact 605 and switch 630 is operated t