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US2412964A - Secrecy communication system - Google Patents

Secrecy communication system Download PDF

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Publication number
US2412964A
US2412964A US500416A US50041643A US2412964A US 2412964 A US2412964 A US 2412964A US 500416 A US500416 A US 500416A US 50041643 A US50041643 A US 50041643A US 2412964 A US2412964 A US 2412964A
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US
United States
Prior art keywords
pulses
wave
valves
masking
signal
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
Application number
US500416A
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English (en)
Inventor
Chatterjea Prafulla Kumar
Houghton Leslie Wilfred
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
STC PLC
Original Assignee
Standard Telephone and Cables PLC
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from GB1637841A external-priority patent/GB580843A/en
Application filed by Standard Telephone and Cables PLC filed Critical Standard Telephone and Cables PLC
Application granted granted Critical
Publication of US2412964A publication Critical patent/US2412964A/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

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Classifications

    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03K—PULSE TECHNIQUE
    • H03K7/00—Modulating pulses with a continuously-variable modulating signal
    • H03K7/02—Amplitude modulation, i.e. PAM
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04K—SECRET COMMUNICATION; JAMMING OF COMMUNICATION
    • H04K1/00—Secret communication
    • H04K1/02—Secret communication by adding a second signal to make the desired signal unintelligible

Definitions

  • the present invention relates to an electrical transmission system for secret communication in which the secret intelligence is masked by the transmission of other signals, which may or may not convey intelligence, in such a way that the existence of the secret communication is hidden.
  • the signal wave actually transmitted (which may, for example, be used to modulate a radio transmitter or carrier frequency system according to known principles) comprises a mixture of a masking wave and a series of regularly repeated short duration pulses which are amplitude modulated by the secret signal.
  • the signals conveyed by the masking wave may be received in any ordinary manner, and the presence of the pulses -conveying the secret information is not suspected. These pulses can only be rendered evident by the use of the special receiving arrangements described in the specication referred to.
  • the present invention is concerned with an improved arrangement at the transmitting end which produces the same type of mixed signal wave without the liability to generate pulses which betray the secret signal.
  • the receiving arrangements may be the same as those described in the above mentioned specification.
  • a secrecy communication system in which the ntelligence to be communicated is transmitted as a, composite electrical wave comprising a masking Wave periodically interrupted for short equal time intervals for the insertion therein of the individual pulses of a pulse train amplitude modulated in accordance with the intelligence wave, the pulses having the same period and duration as the interruptions; provided with a transmitting arrangement comprising means for adding togather the masking wave and the intelligence wave to produce a mixed Wave, means to generate a train of short regularly repeated pulses, means to modulate the amplitude of the pulses in accordance with the mixed wave and means for adding the masking wave to the modulated pulses with such amplitude, sense, and phase'that the proportion of the modulation of the pulses which was due to the masking wave is removed.
  • Figure l shows a ⁇ block schematic diagram of agtransmitting arrangement according to the invention
  • Figures 2 and 3 show explanatory waveform diagrams; and Figure 4 shows a, schematic circuit diagram of a pulse modulator according to the invention.
  • the composite wave is produced by iirst adding together the masking signal and the secret signal waves and using the product to modulate the amplitude of the pulse train.
  • the masking signal wave is then mixed with the modulated pulse train in such a sense that the masking components of the pulse amplitude modulation are balanced out, leaving only the modulation due to the secret signal, while in the intervals between the pulses the masking signal wave is present normally as before. This avoids the necessity of fitting the pulses into the periods cut out of the wave by a separate operation.
  • FIG. 1 shows a block schematic circuit diae gram of a transmitting arrangement according to the present invention.
  • An oscillator l supplies a frequency fp to a pulse generator 2 from which areobtained short pulses having a duration small compared with the intervals between the pulses, the frequency of repetition being fp.
  • the oscillator l also supplies the frequency fp to a source 3 of a masking signal which may be an amplifier to which is supplied a signal at MS, o r it may be, ⁇
  • the secret signal which is to be masked is supplied at SS to an amplifier 5 and thence to a device 6 where it is added to the masking signal wave which already contains the frequency fp which is added ior demodulation purposes at the receiving end, as described in the previously mentioned speciiication.
  • the output of the device 3 will be called the masking signal, in what follows.
  • the mixed signal wave from S is supplied at b to a pulse modulator i for the purpose of amplitude modulating the pulses generated in the device 2, which are supplied to the modulator fi at a.. rIhe output c is connected to an adding device 'I, which is also supplied with the masking signal wave from 3,
  • the output of 'i is then fed to a radio-transmitter or other translating device represented by the block 3.
  • the pulses obtained at c are amplitude modulated by a composite wave comprising a mixture of the masking signal and the secret signal waves.
  • Figure 2 shows a series of such pulses, the dotted outline representing the above mentioned composite Wave.
  • the masking signal wave is added to the modulated pulses in the device l with such an amplitude, sense, and phase that the proportion of the amplitude modulation which was due to the masking signal is neutralised, so that only the modulation due to the secret signal remains.
  • Figure 3 in which the outline of thefull-line curve represents the masking signal wave which when added to the pulses of Figure 2 causes their tips to follow the dotted line curve of Figure 3, which is the curve corresponding to the secret signal.
  • the wave obtained at the output d of the device 'I is the full line curve of Figure 3, which comprises the masking signal interrupted bythe pulses whose tips emergee the secret signal.
  • FIG. 4 This is the same type of wave as is provided at the output of the adding tailed schematic circuit diagram of a preferred L* form of the pulse modulator 4 is shown in Figure 4.
  • This circuit comprises four thermionic amplifying valves of any suitable type (shown as triodes for clearness), designated V1, V2, V3 and V4. to the invention which will be fully described, the circuit also includes conventional operating arrangementsfor the valves well known in the art; and of these A indicates an anode decoupling resistance, G a grid leak resistance, Q a cathode bias resistance, C a by-pass condenser and K a blocking condenser, these all having appropriate values.
  • B represents a suitable resistance for providing cathode bias from the anode potential source I-IT-i- Which is connected to terminal I8.
  • the input terminals for the pulses to be modulated are I II and I2, those for the modulating signal are i3 and Hi, and the output terminals for the modulated pulses are i5 and I6, These pairs of terminals are respectively marked a, b and c to correspond with the markings applied to the pulse modulator i in Figure 41.
  • valves V1 and V2 should be as closely alike as possible, and form one pair, while V3 and V4 should also be alike and form another pair; but they need not be the same as V1 and V2.
  • the valves V1 and V2 are respectively provided with equal anode load resistances R1 and Rz and equal cathode load resistances R3 and R4.
  • the control grids of these two valves are supplied in parallel Besides the special arrangements according with unidirectional pulses (for example positive pulses) from the pulse generator 2 (Fig. 1) through the terminals II and I2.
  • the resistances R1 and R2 being earthed for the signals through the corresponding by-pass condensers C, equal negative pulses will be obtained 'from the anodes oi V1 and V2; and also equal positive pulses Will be obtained from the resistances R3 and R4.
  • the resistances should be so chosen that the positive pulses obtained across R4 are equal in amplitude to the negative pulses obtained across R1.
  • the control grids of the valves V3 and V4 are connected respectively to R1 and R4 as shown so that one of them is energized positively and one negatively. As a result the drop across the common anode rload resistance R5 remains constant, and there will be no output at the terminals I5 and I6.
  • V3 will produce a negative pulse at the output terminals l5 and iii, which is exactly neutralized by the positive pulse produced by Vi, and there will,
  • valves V1 and V2 should bebiased beyond the cut-0E, and this will prevent them from being operated during ythe intervals 4between .the pulses.
  • the anode circuits are decoupled by means of the condensers .C in order to yprevent the modulating signal wave from aiecting the anode voltage of V1.
  • a secrecy communication system in which the intelligence to be communicated is transmitted as a composite ⁇ electrical wave comprising a masking wave periodically interrupted for short equaltime intervals for the insertion therein of the individual pulses of a pulse train amplitude modulated in accordance with the intelligence wave, the pulses having the same period andduration as the interruptions; provided with a transmitting arrangement comprising means for adding together the masking wave and the intelligence wave to produce a mixed wave, lmeans to generate a train of short regularly repeated pulses, means to modulate the amplitude of the pulses in accordance with the mixed wave .and means for adding the masking wave tothe modulated pulses with such amplitude, sense, and phase that the proportion of the modulation of the pulses which was clue .to the .masking wave Yis removed.
  • a system according to claim 1 comprising a' pulse generator controlled by an oscillator for producing the regularly repeated pulses, the masking wave being adapted to contain a sinusoidal wave component derived from the oscillator and having a frequency equal to the pulse repetition frequency.
  • the modulating means comprises a first pair of similar thermionic valves and means to apply the regularly repeated pulses simultaneously to the control grids of the two valves, each valve being provided with an output load resistance so disposed that pulses of equal amplitudes but of opposite signs are produced across the two load resistances, respectively.
  • the modulating means comprises a rst pair of similar thermionic valves, means to apply the regularly repeated pulses simultaneously to the control grids of said two valves, a rst load resistance connected in series with the anode of one valve and a second load resistance connected in series with the cathode of the other valve.
  • the modulating means comprises a first pair of similar thermionic valves, means to apply the regularly repeated pulses simultaneously to the control grids of said valves, a first load resistance connected in series with the anode of one of said valves, a second load resistance connected in series with the cathode of the other of said valves and a second pair of similar thermionic valves having their anodes connected through a common resistance to the source of anode potential and their control grids connected respectively to said rst and second load resistances.
  • the 6 modulating means comprises a first pair of similar thermionic valves, means to apply the regularly repeated impulses simultaneously to the control grids of said two valves and means for applying said masking signal wave to the anode of one of said valves.
  • the modulating means comprises a first pair of similar thermionic valves, means to apply the regularly repeated pulses simultaneously to the control grids of said two valves, a first load resistance connected in series with the anode of one of said valves, a second load resistance connected in series with the cathode of the second said valve, a second pair of similar thermionic valves having their anodes connected through a common resistance to the source of anode potential and their control grids connected respectively to the two load resistances and an output circuit for obtaining modulated output pulses from the anodes oi the said second pair of valves.
  • the modulating means comprises a rst pair of similar thermionic valves, means for biasing said valves beyond the cut-off point, means to apply the regularly repeated pulses simultaneously to the control grids of said two Valves, a rst load resistance connected in series with the anode of one of said valves, a second load resistance connected in series with the cathode of the other of said valves, and a second pair of similar thermionic valves having their anodes connected through a common resistance to the source of anode potential and their control grids connected respectively to said first and second load resistances.

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  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Digital Transmission Methods That Use Modulated Carrier Waves (AREA)
US500416A 1941-12-18 1943-08-28 Secrecy communication system Expired - Lifetime US2412964A (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB1637841A GB580843A (en) 1941-12-18 1941-12-18 Improvements in or relating to secrecy communication systems
GB1493842A GB582709A (en) 1941-12-18 1942-10-23 Improvements in or relating to secrecy communication systems

Publications (1)

Publication Number Publication Date
US2412964A true US2412964A (en) 1946-12-24

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Application Number Title Priority Date Filing Date
US500416A Expired - Lifetime US2412964A (en) 1941-12-18 1943-08-28 Secrecy communication system

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US (1) US2412964A (xx)
BE (2) BE473048A (xx)
FR (2) FR939295A (xx)

Cited By (13)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2460326A (en) * 1945-02-17 1949-02-01 Clarence M Woodruff Transmitter
US2466230A (en) * 1946-02-09 1949-04-05 Stromberg Carlson Co Pulse time modulation system
US2589617A (en) * 1947-07-07 1952-03-18 Alfred C Kowalski Pulse amplitude modulation communication system
US2616975A (en) * 1947-02-06 1952-11-04 Rca Corp Time division multiplex system
US2664462A (en) * 1949-08-31 1953-12-29 Rca Corp Multiplexed signal transmission
US2699544A (en) * 1949-03-30 1955-01-11 Olive S Petty Distance measuring system
US2836657A (en) * 1944-11-20 1958-05-27 Gen Electric Secrecy communication system
US3399273A (en) * 1963-04-23 1968-08-27 Csf Ciphering system
US3560660A (en) * 1966-05-05 1971-02-02 Sits Soc It Telecom Siemens Time-allocation communication system with scrambling network
US3569625A (en) * 1961-04-27 1971-03-09 Us Navy Telemetry data transmission system
US3991268A (en) * 1948-12-24 1976-11-09 Bell Telephone Laboratories, Incorporated PCM communication system with pulse deletion
US4177485A (en) * 1944-09-06 1979-12-04 Prehn Lawrence D Facsimile apparatus
GR890100620A (en) * 1988-09-30 1990-10-31 Datapac Srl Method and device for sealing sheets of paper

Cited By (13)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4177485A (en) * 1944-09-06 1979-12-04 Prehn Lawrence D Facsimile apparatus
US2836657A (en) * 1944-11-20 1958-05-27 Gen Electric Secrecy communication system
US2460326A (en) * 1945-02-17 1949-02-01 Clarence M Woodruff Transmitter
US2466230A (en) * 1946-02-09 1949-04-05 Stromberg Carlson Co Pulse time modulation system
US2616975A (en) * 1947-02-06 1952-11-04 Rca Corp Time division multiplex system
US2589617A (en) * 1947-07-07 1952-03-18 Alfred C Kowalski Pulse amplitude modulation communication system
US3991268A (en) * 1948-12-24 1976-11-09 Bell Telephone Laboratories, Incorporated PCM communication system with pulse deletion
US2699544A (en) * 1949-03-30 1955-01-11 Olive S Petty Distance measuring system
US2664462A (en) * 1949-08-31 1953-12-29 Rca Corp Multiplexed signal transmission
US3569625A (en) * 1961-04-27 1971-03-09 Us Navy Telemetry data transmission system
US3399273A (en) * 1963-04-23 1968-08-27 Csf Ciphering system
US3560660A (en) * 1966-05-05 1971-02-02 Sits Soc It Telecom Siemens Time-allocation communication system with scrambling network
GR890100620A (en) * 1988-09-30 1990-10-31 Datapac Srl Method and device for sealing sheets of paper

Also Published As

Publication number Publication date
FR939295A (fr) 1948-11-09
FR939428A (fr) 1948-11-15
BE473048A (xx)
BE471102A (xx)

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