US3696207A - System for the transmission of intelligence by means of scrambled audiosignals - Google Patents

System for the transmission of intelligence by means of scrambled audiosignals Download PDF

Info

Publication number
US3696207A
US3696207A US34728A US3696207DA US3696207A US 3696207 A US3696207 A US 3696207A US 34728 A US34728 A US 34728A US 3696207D A US3696207D A US 3696207DA US 3696207 A US3696207 A US 3696207A
Authority
US
United States
Prior art keywords
frequency
shift
receiver
transmitter
control 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
US34728A
Other languages
English (en)
Inventor
Seth Johan Ronald Lundin
Bengt Harry Bjorkman
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.)
US Philips Corp
Original Assignee
US Philips Corp
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 SE06921/69A external-priority patent/SE354394B/xx
Priority claimed from SE06920/69A external-priority patent/SE353633B/xx
Application filed by US Philips Corp filed Critical US Philips Corp
Application granted granted Critical
Publication of US3696207A publication Critical patent/US3696207A/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

Links

Images

Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04K—SECRET COMMUNICATION; JAMMING OF COMMUNICATION
    • H04K1/00—Secret communication
    • H04K1/003—Secret communication by varying carrier frequency at or within predetermined or random intervals

Definitions

  • the present invention relates to a system for the transmission of intelligence by means of scrambled audiosignals, comprising a transmitter and a receiver each of which includes an oscillator, a shift register connected in feedback and controlled by a shift pulse generator, means connecting said shift register to said oscillator to produce a predetermined frequency variation of said oscillator output signal, means in said transmitter for combining the oscillator output signal with the audiosignal to produce said scrambled audiosignal to be transmitted, and means in said receiver for combining said oscillator output signal with said received scrambled audiosignal to effect demodulation thereof.
  • the shift registers serve as control elements, and they will due to their feedback continuously repeat their cycle of operation, the duration of which is determined by the number of stages in the register.
  • the output of the last stage of the register is a rectangular wave having an irregular pattern which is produced once for each cycle of operation.
  • the magnitude of the distortion in each moment is determined by the stored digit represented by the condition of the individual stages.
  • the individual stages of the shift register can for this purpose be connected through an adding network to the frequency determining circuit of the oscillator, the output frequency of which is combined with the audiosignals to be transmitted.
  • the receiver there is a similar oscillator controlled by a shift register which is connected in the same manner as at the transmitter end. In order that the demodulation shall give the desired result the frequency added in the receiver must in each moment be exactly equal to the frequency added in the transmitter, i.e. the shift registers must operate synchroneously.
  • the object of the invention is to provide a system of the above indicated type in which a minimum of information is required for the synchronization and in which the band width required for the transmission of this information is narrow so that this information can be transmitted through conventional speech channels.
  • the transmitter further comprises means for adding to the scrambled audiosignal a control signal derived from the shift pulse generator of the transmitter, said control signal having a frequency within the frequency band of the audiosignals to be transmitted and a phase which is representative of the shift pulses produced by the shift pulse generator of the transmitter and in that the receiver further comprises means adapted to select the said control signal before said demodulation and means for applying said selected control signal to the shiftpulse generator of the receiver for controlling the said generator to establish phase coincidence between the output signal of said generator and said control signal.
  • synchronization only requires transmission of one single discrete frequency, namely the sinus shaped fundamental component of the control voltage from which the shift pulses at the transmitter are derived. This ensures that the shifting occurs synchronously in the receiver and transmitter.
  • Setting of the mutual phase of the shift registers in their respective cycles of operation takes place in special intervals, fir example one single interval before information transmission, by means of pulses of a single discrete repetition frequency and which pulses define a predetermined starting condition of the register of the transmitter.
  • the demodulated frequency variations in the demodulated frequency can make it necessary to transmit two discrete frequencies for the synchronization, the useful information representing the time positions for the shift pulses of the register in the transmitter being formed by the difference between the two transmitted frequencies, which difference signal varies with possible changes in the absolute values of the frequencies.
  • FIG. 1 shows a block diagram of a transmission equipment for transmission of scrambled speech signals, in accordance with the invention
  • FIG. 2 shows an example of a pulse signal derived from a shift register included in the equipment according to FIG. 1, which signal is utilized for the speech scrambling and
  • FIG. 3 shows some voltage curves appearing in the receiver of the device according to FIG. 1.
  • FIG. 4 shows a modification of the signal input circuit of the transmitter of applicantsinvention.
  • FIG. 1 the transmitter is shown on the left and the receiver on the right hand side of the dotted lined.
  • the speech signal from a microphone 10 is fed to a modulator 1 l in the form of a symmetric mixer.
  • the speech signal is mixed with the output voltage from an oscillator 12, the frequency of which is varied between different levels.
  • the instantaneous frequency of the oscillator 12 is determined by a continuously operating shift register 13, which is connected in feedback and the individual stages of which are connected to the frequency determining means of the oscillator 12 through an adding device 14.
  • the shift register 13 which can be connected in the same manner as shown in the Patents (Swedish Patent applications 1 1907/67, PI-lN 1863 and 12,524/67, PHN 1906) is operated by shift pulses from a shift pulse generator consisting of a driving oscillator 15 and a divider 16 arranged between the driving oscillator and the shift input of the shift register.
  • the driving oscillator 15 may for example operate at a frequency of 2.5 kc/s and the divider 16 can produce a frequency division of l 4, whereby the shift register will operate at a shift frequency of 625 c/s.
  • the oscillator 12 can operate conveniently at a center frequency lying at the upper limit of the speech spectrum, for example 3 kc/s and the frequency jumps produced by the shift register 13 may for example amount to maximum 400 c/s, whereby the oscillator will deliver an output frequency which varies between different levels in an irregular but predetermined manner between the limits 26 and 34 kc/s.
  • An example of the frequency variation of the oscillator 12 as function of time is shown in FIG. 2.
  • the utilized mixing product from the mixer 11 is the lower side band, i.e. the instantaneous frequency of the oscillator 12 minus the frequency of the speech signal.
  • the mixer 11 will therefore also produce an inversion of the speech spectrum, which makes it difficult to interprete such a distorted message without the proper listening apparatus.
  • the scrambled speech signal can be transmitted directly or by modulation on a carrier to the receiver.
  • the distorted speech signal is fed through a filter 17 to a modulator or mixer 18 of the same construction as the modulator 11 in the transmitter.
  • filter 17 To the mixer 18 is also applied the output voltage from an oscillator 19, which corresponds to the oscillator 12 in the transmitter. Oscillator 19 is frequency controlled from a shift register 20 via an adding device 21.
  • the shift pulses for the register 20 are produced by a shift pulse generator comprising a driving oscillator 22 which is connected to the shift input of the register 20 through a divider 23.
  • the shift register 20 is connected in the same manner as the shift register 13 in the transmitter and produces the same pulse pattern.
  • the shift register 13 and 20 operate in synchronism demodulator 18 will add a frequency which in each moment is exactly equal to the frequency applied to the modulator 11 in the transmitter. Demodulator 18 will thus produce a mixing product which corresponds to the initial speech signal.
  • control signal is derived from the divider 16 and applied to register 13. In the given example this control signal has a frequency of 625 c/s.
  • This control signal now is also fed through a lead 24 directly to a device 32, where it is combined with the scrambled speech signal.
  • the said control signal having the shape of a rectangular wave can if desired be filtered before being combined with the speech signal, so that only the sinus shaped fundamental component is transmitted.
  • the transmission of this control signal may be continuous as long as speech signals are transmitted or if desired may be transmitted only intermittently if the shift pulse generator of the receiver is sufficiently frequency stable.
  • the incoming signal consisting of the scrambled speech signal and the control signal of the shift register is as mentioned fed through a filter 17. This is so shaped that the said control signal is selected and fed to a phase detector 25. Furthermore the filter 17 ensures that the control signal cannot occur at the input of demodulator 18. Filter 17 has a very narrow band width amounting to some cycles per second on each side of the frequency of the control signal. The suppression of the speech signal produced within this band will not really influence the quality of the speech signal.
  • filter 17 is constituted by an amplifier 26 which is fed back through a double T-net 27 and furthermore there is an input resistance 28 and a resistance 29 in the transmission path for the speech signal and a resistance 30 which is connected in feedback from the output of the amplifier to the output side of the resistance 29.
  • phase detector 25 the selected control signal of 625 c/s is compared with the output signal of divider 23 which is used for shifting the register 20.
  • the output signal of the phase detector representing the phase difference between the two compared signals is after amplification in an amplifier 31 fed to the frequency determining means of the oscillator 22.
  • the output signal of phase detector 25 tends to make the phase difference equal to zero by negative feedback. Accordingly the control signal at the output of divider 23 will be in phase with the corresponding control signal at the output of divider 16 in the transmitter and the two shift registers will be shifted exactly synchronously.
  • pulses time synchronized with the cycle of shift register 13 in the transmitter are fed to the line during a speech-free interval, preferably an interval preceding the transmission of speech signals.
  • The'se pulses are in the shown embodiment derived from the driving oscillator 15 and thus have a frequency 25 kc/s.
  • the length of the pulses and their moment of occurrence is determined by an AND-gate 35 connecting the output of oscillator 15 to the device 32.
  • the gate 35 is opened and closed by means of a flip-flop 36, which is controlled by two decoder units 37, 38 in turn.
  • Decoder unit 37 is connected to the set-input of bistable flip-flop 36 through and AND-gate 39, while the second decoder unit 38 is connected to the reset-input of flip-flop 36.
  • AND-gate 39 is enabled by means of the voltage from a monostable circuit 40.
  • Said monostable circuit 40 is controlled by means of a switch 41, which produces a trigger pulse which is fed through a differentiating circuit 42 to said monostable circuit 40.
  • the switch 41 is for example actuated when the operator pushes the starting button at the beginning of speech signal transmission.
  • the decoder units 37 and 38 are connected to all stages in the shift register 13 and thus sense the instantaneous content of the register. Each decoder unit is adapted to produce an output pulse in response to a certain content of the register.
  • the decoder unit 38 for example produces an output pulse the moment all stages in the register 13 have been switched, i.e. have assumed a position which is designated binary l Decoder unit 37 produces an output pulse a number of shift pulse periods prior to said moment.
  • Provided gate 39 is open flip-flop 36 will be triggered when the content of shift register 13 is such that decoder unit 37 reacts. A small interval later the condition is reached for which the decoder unit 38 is sensitive, whereby the flip-flop 36 is reset.
  • the pulse produced by monostable circuit 40 has a duration such that during this pulse a number, for example 3-5, synchronization pulses are passed onto the line. The moment monostable circuit 40 returns to its original state gage 39 will be closed, so that flip-flop 36 can no longer be triggered and the synchronization pulses will cease since they cannot pass gate 35.
  • the synchronization pulses are selected by means of filter 45, which is tuned to a frequency of 2,500 c/s of thepulses.
  • Filter is constituted by an amplifier 46 which is connected in feedback through a double T-network 47.
  • the selected synchronization pulses are applied to an integrator 48 consisting of an amplifier 50 connected in feedback through a capacitor 49 and having two diodes 51, 52 arranged at the input side.
  • the output voltage of integrator 49 increases stepwise in rhythm with the periods of the applied AC-voltage.
  • the integrator has a limiter, for limiting the integrator output voltage to a certain level.
  • the integrator 48 controls a Schmitt-trigger stage 54, which produces an output voltage as long as the output voltage of the integrator exceeds a certain level. After amplification in an amplifier this voltage pulse from the Schmitt-trigger stage 54 is fed through an AND- gate 56 to the control input of shift register 20. At the appearance of a voltage pulse from gate 56 the individual stages of the shift register 20 are forced to assume a certain position, for example in the given example all the stages are set in the position l Immediately after this pulse the shift register is released so that it starts to operate in rhythm with the shift pulses from divider 23.
  • the output voltage from the integrator 48 is shown in FIG. 3a and the output voltage from the Schmitt-trigger stage is shown in FIG. 3b.
  • the level of the output voltage of integrator 48, at which the Schmitt-trigger stage is activated, is in FIG. 3a designated S.
  • the moment t coincides with the beginning of a synchronization pulse, when the voltage at the output of integrator 48 begins to increase.
  • the Schmitttrigger stage 54 is switched.
  • the synchronization pulse ceases and immediately thereafter, at the moment t., the voltage at the output of the Schmitt-trigger stage disappears.
  • Gate 56 is controlled by means of a counter 57 to which the synchronization pulses appearing at the output of the amplifier 55 are applied through an AND- gate 58.
  • the counter 57 is connected in feedback to an input of the gate 58 in a manner such that the gate is automatically closed the moment a certain number, for example 3-5 synchronization pulses, have been counted.
  • gate 56 will be kept open. When the predetermined number of pulses has been counted gate 56 is closed and thus no longer able to pass pulses to the shift register 20.
  • the counter 57 is reset by means of an integrator 59 of the same construction as the integrator 48.
  • integrator 59 is controlled by the selected control signal of 625 0/5 used for synchronization of the shifting of the registers.
  • the voltage is built up at the output of the integrator 59 in the same manner as shown for integrator 48. The voltage is then kept on this level during the whole speech, whereby the counter 57 can carry through the described operation cycle. Ceasing of the voltage from integrator 59 at the end of speech signal transmission results in zeroing of the counter 57.
  • the operation is as follows.
  • the monostable circuit 40 When the operator pushes the button for speech signal transmission illustrated by the switch 41 in FIG. 1, the monostable circuit 40 will be triggered so that gate 39 is opened.
  • Flip-flop 36 is triggered when the content of shift register 13 is such that the decoder unit 37 produces a setting signal and immediately thereafter the flip-flop 36 is reset when the register content is such that decoder unit 38 produces a reset signal.
  • gate 35 is enabled to pass synchronization pulses having a recurrence frequency of 2,500 c/s to the line. Gate 35 is closed after a predetermined number of synchronization pulses have been fed to the line.
  • each individual synchronization pulse produces an output voltage (FIG. 3a) at the output of integrator 48.
  • the shift register will receive a voltage on its control input via the amplifier 55 and gate 56, which voltage compulsorily sets the stages in the register 20 in the predetermined position.
  • the shift register 20 will be released so that it starts to operate on the shift pulses from the divider 23.
  • the starting condition of register 20 which is set during the synchronization pulse is chosen to be equal to the condition, for which the decoder unit 38 is responsive.
  • the shift register 20 Since the decoder unit 38 determines the moment when the synchronization pulse is interrupted the shift register 20 will be set to the same starting condition as the shift register 13 at the moment of interruption of the synchronization pulse. After reception of a predetermined number of synchronization pulses gate 56 will be closed and the register 20 will thereafter operate in response to the shift pulses from divider 23. Provided that the shift pulses maintain their synchronization and that the last synchronization pulse has produced correct setting of the shift register 20, the shift registers in the transmitter and receiver will thereafter operate in complete synchronism.
  • the described system with transmission of one single discrete frequency representing the control signal of the shift register on the transmitter side is not reliable.
  • the frequency of the control voltage after demodulation can vary somewhat on each side of the desired frequency. But as the information lies in the phase of the control voltage, frequency variations can of course not be allowed.
  • This difficulty can be overcome by transmitting instead of one single frequency two frequencies, for example 600 and 1,200 c/s, in which case the difference between these two signals carries the information about the phase position of the control voltage of the shift register on the transmitter side. Even if the absolute value of the transmitted signals should vary somewhat the difference between the signals will be constant and transmit the required information to the receiver.
  • a further improvement of the secrecy may be obtained by inserting a filter 33 (see FIG. 4) between the microphone 10 and the modulator 11, said filter being a lowpass filter which acts as a damping network for mainly the higher frequencies of the speech signal, the cut-off frequency of said filter being situated within the frequency band to be transmitted.
  • this cut-off frequency is for instance 1 kc/s.
  • the two decoder units in the transmitter can be adjustable so that the synchronization pulses will appear at different moments of the operation cycle of the shift register in the transmitter. In the receiver this can be compensated by means of a time delay between the device that detects the synchroniza- 8 tion pulses and the setting device producing the predetermined setting of the shift register in the receiver.
  • the described system is not limited to the transmis 'sion of scrambled speech signals but can also be used where the information has to be kept secret, for example in data transmission by audiosignals or frequency shift.
  • the system according to the invention can also be modified for transmission using the three-out-of-five code or the like, where each information element is represented by a frequency within the audio spectrum.
  • a system for the transmission of intelligence signals by means of scrambled audiosignals comprising a transmitter and a receiver, said transmitter comprising signal input means for said intelligence signals, a source of auxiliary information signals having a periodic pulse pattern not correlated with said intelligence signals, said source comprising an oscillator, a feedback connected shift register coupled to said oscillator to produce a predetermined frequency variation by varying the frequency of said oscillator, and a frequency shift generator coupled to control said shift register and provide a control signal at a frequency within the frequency band of said intelligence signals and a phase representing the shift pulses produced by said shift pulse generator, means for combining said intelligence signals and said auxiliary information signals to produce a scrambled audiosignal, means for adding said control signal to said scrambled audiosignals for transmission to said receiver, said receiver comprising signal input means for receiving said scrambled audiosignals with said control signal, means for separating said scrambled audiosignals from said control signal, a source of auxiliary information signals having a periodic pulse pattern identical to the periodic pulse pattern
  • the frequency shift generator of said receiver further comprises a closed loop comprising a phase detector for receiving said control signal and the output of said frequency shift generator to control said frequency shift generator thereby maintaining a predetermined mutual phase position between said control signal and the output of said frequency shift generator.
  • control signal is formed by the difference signal obtained by comparison of two signals having a difference frequency within the frequency band of the intelligence signal.
  • synchronizing transmitter is provided with means for synchronizing the shift registers controlled by the shift registers for generating and transmitting to the receiver during at least one interval at the beginning of said intelligence signal transmission, pulses having a frequency within the transmitted frequency band, said pulses being synchronized in time with the shift register in said transmitter so that it appears at a predetermined condition of said register, and the receiver is provided with means for receiving said synchronizing pulse to ensure the corresponding setting of the shift register of the receiver in the period of time determined by the pulse thereby syncrhonizing the periodic pulse pattern of said receiver with the periodic pulse pattern of the transmitter. trailing 5.

Landscapes

  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Synchronisation In Digital Transmission Systems (AREA)
  • Transmitters (AREA)
  • Reduction Or Emphasis Of Bandwidth Of Signals (AREA)
US34728A 1969-05-14 1970-05-05 System for the transmission of intelligence by means of scrambled audiosignals Expired - Lifetime US3696207A (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
SE06921/69A SE354394B (enrdf_load_stackoverflow) 1969-05-14 1969-05-14
SE06920/69A SE353633B (enrdf_load_stackoverflow) 1969-05-14 1969-05-14

Publications (1)

Publication Number Publication Date
US3696207A true US3696207A (en) 1972-10-03

Family

ID=26654737

Family Applications (1)

Application Number Title Priority Date Filing Date
US34728A Expired - Lifetime US3696207A (en) 1969-05-14 1970-05-05 System for the transmission of intelligence by means of scrambled audiosignals

Country Status (10)

Country Link
US (1) US3696207A (enrdf_load_stackoverflow)
JP (1) JPS4932601B1 (enrdf_load_stackoverflow)
AT (1) AT312691B (enrdf_load_stackoverflow)
BE (1) BE750302A (enrdf_load_stackoverflow)
CA (1) CA919321A (enrdf_load_stackoverflow)
CH (1) CH519831A (enrdf_load_stackoverflow)
DE (1) DE2021941A1 (enrdf_load_stackoverflow)
FR (1) FR2047764A5 (enrdf_load_stackoverflow)
GB (1) GB1257584A (enrdf_load_stackoverflow)
NL (1) NL7006806A (enrdf_load_stackoverflow)

Cited By (14)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3808536A (en) * 1972-04-12 1974-04-30 Gen Electric Co Ltd Communication scrambler system
US3824468A (en) * 1966-09-14 1974-07-16 Philips Corp System for transmitting information in the prescribed frequency-band
US3886313A (en) * 1972-09-29 1975-05-27 Datotek Voice security method and system
US3893031A (en) * 1972-11-08 1975-07-01 Boeing Co Synchronization system for voice privacy unit
US3909534A (en) * 1973-09-07 1975-09-30 Boeing Co Voice privacy unit for intercommunication systems
US3921151A (en) * 1971-06-21 1975-11-18 Patelhold Patentwerwertungs & Apparatus for enciphering transmitted data by interchanging signal elements of the transmitted data without overlapping or omitting any elements within the transmitted signal train
US4058677A (en) * 1974-04-26 1977-11-15 Lear Siegler, Inc. Sound scrambling equipment
US4074079A (en) * 1976-06-02 1978-02-14 Bell Telephone Laboratories, Incorporated Coin telephone antifraud system
US4133977A (en) * 1977-02-25 1979-01-09 Lear Siegler, Inc. Voice scrambler using syllabic masking
US4149035A (en) * 1976-06-01 1979-04-10 Peter Frutiger Method and apparatus for enciphering and deciphering audio information
US4228321A (en) * 1978-05-16 1980-10-14 Bell Telephone Laboratories, Incorporated Privacy transmission system with remote key control
US4268720A (en) * 1979-05-25 1981-05-19 Gte Laboratories Incorporated Scrambler speech transmission and synchronization system
US4761813A (en) * 1977-08-22 1988-08-02 Siemens Aktiengesellschaft Military radar or radio communication system
US4790009A (en) * 1984-10-29 1988-12-06 Victor Company Of Japan, Ltd. Scrambler system

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2401403A (en) * 1943-12-15 1946-06-04 Rca Corp Secret signaling
US3180927A (en) * 1961-09-07 1965-04-27 Itt Cryptosecure transmission system
CH460870A (de) * 1966-09-14 1968-08-15 Philips Nv Ubertragungsanlage mit einer Sendevorrichtung und einer Empfangsvorrichtung zur Informationsübertragung in einem bestimmten Frequenzband

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2401403A (en) * 1943-12-15 1946-06-04 Rca Corp Secret signaling
US3180927A (en) * 1961-09-07 1965-04-27 Itt Cryptosecure transmission system
CH460870A (de) * 1966-09-14 1968-08-15 Philips Nv Ubertragungsanlage mit einer Sendevorrichtung und einer Empfangsvorrichtung zur Informationsübertragung in einem bestimmten Frequenzband

Cited By (14)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3824468A (en) * 1966-09-14 1974-07-16 Philips Corp System for transmitting information in the prescribed frequency-band
US3921151A (en) * 1971-06-21 1975-11-18 Patelhold Patentwerwertungs & Apparatus for enciphering transmitted data by interchanging signal elements of the transmitted data without overlapping or omitting any elements within the transmitted signal train
US3808536A (en) * 1972-04-12 1974-04-30 Gen Electric Co Ltd Communication scrambler system
US3886313A (en) * 1972-09-29 1975-05-27 Datotek Voice security method and system
US3893031A (en) * 1972-11-08 1975-07-01 Boeing Co Synchronization system for voice privacy unit
US3909534A (en) * 1973-09-07 1975-09-30 Boeing Co Voice privacy unit for intercommunication systems
US4058677A (en) * 1974-04-26 1977-11-15 Lear Siegler, Inc. Sound scrambling equipment
US4149035A (en) * 1976-06-01 1979-04-10 Peter Frutiger Method and apparatus for enciphering and deciphering audio information
US4074079A (en) * 1976-06-02 1978-02-14 Bell Telephone Laboratories, Incorporated Coin telephone antifraud system
US4133977A (en) * 1977-02-25 1979-01-09 Lear Siegler, Inc. Voice scrambler using syllabic masking
US4761813A (en) * 1977-08-22 1988-08-02 Siemens Aktiengesellschaft Military radar or radio communication system
US4228321A (en) * 1978-05-16 1980-10-14 Bell Telephone Laboratories, Incorporated Privacy transmission system with remote key control
US4268720A (en) * 1979-05-25 1981-05-19 Gte Laboratories Incorporated Scrambler speech transmission and synchronization system
US4790009A (en) * 1984-10-29 1988-12-06 Victor Company Of Japan, Ltd. Scrambler system

Also Published As

Publication number Publication date
NL7006806A (enrdf_load_stackoverflow) 1970-11-17
CA919321A (en) 1973-01-16
DE2021941A1 (de) 1972-01-13
BE750302A (fr) 1970-11-12
AT312691B (de) 1974-01-10
CH519831A (de) 1972-02-29
JPS4932601B1 (enrdf_load_stackoverflow) 1974-08-31
GB1257584A (enrdf_load_stackoverflow) 1971-12-22
FR2047764A5 (enrdf_load_stackoverflow) 1971-03-12

Similar Documents

Publication Publication Date Title
US3696207A (en) System for the transmission of intelligence by means of scrambled audiosignals
US4361890A (en) Synchronizing system
US4545061A (en) Synchronizing system
US2392546A (en) Pulse modulation receiver
US4188580A (en) Secure communication system
US2497411A (en) Pulse transmission system
US4075660A (en) Pay television system with synchronization suppression
US4047108A (en) Digital transmission system for transmitting speech signals at a low bit rate, and transmission for use in such a system
GB1073568A (en) Multiplex pulse communication system
US4305152A (en) Security communication system
US3499995A (en) Frequency and time division multiplex signalling systems using successive changes of frequency band and time slot
US3746991A (en) Remote control communications system
US2795650A (en) Compandor control system
US3493866A (en) Frequency stepped phase shift keyed communication system
US3440353A (en) Radio-transmission system
US2415919A (en) Multiple pulse characteristic communication system
GB1452433A (en) Communication system incorporating signal delay
US4087627A (en) Clock regenerator comprising a reversible shift register and a controllable frequency divider
GB1261447A (en) Multiplex transmission system
US3629505A (en) Transmission system for the transmission of information in a prescribed frequency band
GB1502498A (en) Transmission system for pulse signals
US3612770A (en) Transmission system comprising a transmitter and a receiver for the transmission of information in a prescribed frequency band and transmitters and receivers to be used in said system
US3909527A (en) Frequency shift keying system and method
US4214126A (en) Cadence suppression system
US3902014A (en) Circuit arrangement for regenerating the modulation timing of a line signal in a data transmission equipment