US2426225A - Communication system - Google Patents

Communication system Download PDF

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Publication number
US2426225A
US2426225A US531859A US53185944A US2426225A US 2426225 A US2426225 A US 2426225A US 531859 A US531859 A US 531859A US 53185944 A US53185944 A US 53185944A US 2426225 A US2426225 A US 2426225A
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US
United States
Prior art keywords
pulses
wave
series
phase
odd
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
US531859A
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English (en)
Inventor
Irving A Krause
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
Federal Telephone and Radio Corp
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 to NL81626D priority Critical patent/NL81626C/xx
Priority to BE479062D priority patent/BE479062A/xx
Application filed by Standard Telephone and Cables PLC filed Critical Standard Telephone and Cables PLC
Priority to US531859A priority patent/US2426225A/en
Priority to GB9320/45A priority patent/GB591884A/en
Priority to FR951383D priority patent/FR951383A/fr
Application granted granted Critical
Publication of US2426225A publication Critical patent/US2426225A/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

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    • 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
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S1/00—Beacons or beacon systems transmitting signals having a characteristic or characteristics capable of being detected by non-directional receivers and defining directions, positions, or position lines fixed relatively to the beacon transmitters; Receivers co-operating therewith
    • G01S1/02—Beacons or beacon systems transmitting signals having a characteristic or characteristics capable of being detected by non-directional receivers and defining directions, positions, or position lines fixed relatively to the beacon transmitters; Receivers co-operating therewith using radio waves
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B14/00—Transmission systems not characterised by the medium used for transmission
    • H04B14/02—Transmission systems not characterised by the medium used for transmission characterised by the use of pulse modulation
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04J—MULTIPLEX COMMUNICATION
    • H04J3/00—Time-division multiplex systems
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04K—SECRET COMMUNICATION; JAMMING OF COMMUNICATION
    • H04K1/00—Secret communication
    • H04K1/006—Secret communication by varying or inverting the phase, at periodic or random intervals

Definitions

  • the present invention relatesto communication systems yand more particularly to a communication system having means for preventing or ren,- dering more diicult unauthorized reception of the transmitted intelligence.
  • One object of the invention is to provide a method and means ifor modulating a pulse subcarrier so that the modulating intelligence will be undetectable by the.usual receiving apparatus;
  • Another object-of the invention isy to provide a method and means-for receiving and detecting such modulated pulses, and for minimizing interference.
  • One of the -features of ⁇ the invention is to provide means for generating a train of pulses constituting a sub-.carrier vwave, modulating, either by amplitude, time or other pulse characteristic, the odd pulsesof the train out of ,phase with the even pulses by a signal-wave representing the intelligence which it is desiredto transmit, and recombining the modulated pulses in theorder of their generation.
  • An additional feature of the invention comprises providing means ior reoeivingthe vmodulated pulses at a point remote from the transmission thereofseparating the odd group of pulses from the even group,.demodulating,and/ or filtering to obtain theV audio Wave defined thereby, shifting the phase of one of the Waves by an amount sufficient for recombiningv with the other wave, and reproducing the intelligence thereof.
  • a further-feature of the invention is to provide, in addition to the dilierent phase modulationof the odd and even pulses, a further modulating energylin the form of. a .masking Wave,;this additional energy being applied in a vmanner to the odd and evenpulses. so that by inversion and mixing or-direct mixingl of the tvlol audio waves produced from the odd vand even pulses, as the case may be, the masking wave is removed fromi the desired intelligence Wave.
  • Fig. 1V is a circuit diagram of a preierrediorm of transmitter lembodying the .present invention
  • Fig. 2 is a set of curves usedjn explaining the operation of the circuit of Fig. l;
  • Fig. 3 is a circuit diagram voi a preferred -orm of receiver embodying the, present invention.
  • Fig. 5 isanalternl tive form of demodulator for use in thecircuit of Fig. 3; and 5 Fig. 6 is a graphical villustration used in explaining 'the operation of the demodulator -oi Fig. 5.
  • Fig.l 1 isv shown argenerator 4 having a substantially sine Wave output .such as indicated by the waveform 6.
  • This wave liA is :of sub-carrier frequency, that is, vlovverfthan the Y'frequency 'oi the usual R.. F. or ultra high frequency carrier wave but higher than that of an audio signal.
  • A' know Wave Shaper 8 translates the sine Wavev (i .into asubstantially square wave I0.
  • a known Wavev inverter :l2 inverts by 130 the square'wavezl asv indicated by square wave lll.
  • Theshaper 8 and' invertor l2 may be replaced byV ar A,multivibrationv circuit wherein square Waves vof opposite lpolarity 4may be obtained.
  • Yoi wavezshaper 8 and inverter I2 areffedto-two differentiators ⁇ Hi and I8, respectively,foi theLcharacter adaptedto translate each square vpulse portion of the'vvaves in and I4. into two sets :of Anarrowvzidth positivel and negative pulses ⁇ as indicated .at .20 and,y 2,2, respectively.
  • the pulses 2l) and 2,2 are applied to two tetrodes where the negative p lses areelirninated and the postive ⁇ pulses are amplitude .modulated This isaccomplished by biasing .each 'of the two tetrodes N71-,and V2 to cut-(oli.
  • the pulses may be further modulated by a given masking signal, the further modulation being added to the pulse output from tubes V1 and vV2 in proper phase relation according to the time spacing of successive pulses.
  • This further modulation may take the form of a saw-tooth wave 42 from source 43 applied to the mid-point of the secondary winding of transformer y28 Iby connection 44.
  • the saw-tooth voltage Wave 42 thereby energizes both screen grids 24 and 2t in phase, as contrasted to the out-of-phase energization of these grids by the audio signal input taken across the ends of the transformer secondary Winding, Y
  • Curves a and b illustrate the pulse outputs 36 and 32 of tubes V1 and V2, respectively, in the absence of any modulation.
  • An audio modulating signal is shown in curve c, the solid -line 45 representing the voltage at one end of the secondary Winding of transformer 28, and the broken line 4l representing the voltage at the other end of the Winding.
  • the resulting Wave 35 appearing at point 34 is represented byl Curve
  • the in-phase masking Wave 42 is shown in g, and its effect on the output wave f is shown in h, both odd and even pulses being modulated in phase in the order ofY their generationV as eX- plained above. While the pulses of the curves of Fig. 2 have all been drawn as being of positive polarity, it will be understood that their actual polarity according to the-circuit of Fig. 1 will be as indicated at the diierent points in the circuit.
  • the masking Wave 42 maybe regarded as having the same eiect on the transmitted pulses as a ⁇ non-pulse interference signal such, for example, as an amplitude modulated carrier.
  • FIG. 3 A form of receiver according to the present invention is shown in Fig. 3. IThe energy transmitted from antenna 45 of Fig. l, after being received on antenna 46, is passed through detector 48.
  • the detector 48 demodulates the R.F. carrier energy supplied by translator 38 into a series of sub-carrier pulses substantially ⁇ identical to the pulse train 3S of Figs. 1 and 2.
  • Receiving the pulse output of detector 48 are a rst keyer 5G, a second keyer 52 andra timer circuit 54.
  • Keyer D handles only the odd pulses of thev train while keyer 52 handles only the even pulses.
  • Keyer 50, keyer 52 and timer 54 each' include an electron discharge tube biased to cut-oir" as illustrated.
  • the ⁇ received pulses Will ⁇ be passed through a circuit 58 to the grid of a triode 65 constituting one element of ay multivibrator k62.
  • Multivibrator 62' is provided with a second triode $4, 'the grids and plates of thetwo'tubes beingcross-'connected in normal manner.
  • Multivibrator 62 is adjusted to operate at onehalf the pulse rate, the pulses received on the grid of triode 6!) over circuit 58 serving to key the operation of the multivibrator at one-half the two plate circuits of the multivibrator 62 are ccnnected to screen grids y66 and 68 in the electron discharge devices of the rst keyer circuit 55 and the second keyer circuit 52, respectively.
  • the screen grid 66 in the rst keyer tube l is alternately driven positive and negative at the rate of operation of the multivibrator.
  • the same cycle of operation applies to the screen grid S8 of the secondkeyer tubeV 12, except that when grid is driven positively the grid 68 is driven negatively and vice versa.
  • a pair of resistance-condenser combinations 22 and 84 form parts of the plate circuits of keyers 59 combinations 82 and B4 are chosen of such values that the time constants of the combinations operate to ⁇ filter out the pulses, thereby reproducing with ra minimum of distortion the audio envelope Wave representing the intelligence applied to the-primary of transformer 28 of Fig. 1.
  • the audio Waves reproduced bythe tvvo keyer cir cuits at their output connections 15 and Il are Y 180out of phase.v
  • a phase invertor 'I6 for 180 inversion and then combining the inverted wave output by connection 'i9 to the wave of output'connection 15 a more accurate reproduction of the intelligence VWave is eiected than that represented by the separate outputs of keyer circuits 59 and 52.
  • the combined audio wave is then amplified at i8 and applied to speaker 8U.
  • either of the audio YWaves appearing in the plate circuits of keyers 5i) and 52 defines the transmitted intelligence.
  • the purpose of mixing the two audio Waves is to reproduce the intelligence to a, higher degree of accuracy than is possible through theV utilization of either wave alone.
  • the output of one of the keyer circuits may, of course, be applied directly to amplifier '18 and subsequently reproduced'. This would dispense with the necessity Vof employing a second keyer circuit, although as previously and 52,V respectively.
  • the elements of these mentioned, accuracy .of definition would be sacn riced to a certain degree.
  • ! and 52 must be employed.
  • the masking signal and/or interference signal present on the same carrier, asithe .case may be is. appliedxin phase to both odd and even pulses. If nowthe even pulseenvelope wave .is phase inverted inthe receiver by inverting circuit 1B, the mixing of vthe two envelopesin amplifier i8 will cancel outthe masking signal and. any such interferencelsignal leaving only tthe audio modulation representing the desired intelligence.
  • the masking signal d'2 may itself represent' intelligence.
  • the odd and even envelope waves may be mixed directly by moving switch contact 85 from contact 85 to contact Si thereby ley-passing phase invertor T6. This would cancel the signals applied to the pulses through the primary of transformer 23, Fig. l., leaving the signal applied to the center tap of the secondary of the transformer 28.
  • either of the vmodulating input signals ⁇ of Fig. l may carrythe actual message, or, if' desired, they may represent separate messages.
  • the signal @l2 is the desired intelligence, then interference minimizing must be carried out by a' suitable blo cking'arrangement.
  • FIG. 4 illustrates a P. T. M. (pulse'time modulation) transmitter including a generator it@ for producing a base wave
  • the output of phase shifter Hill is fed yto one primary winding
  • Transformer we constitutes part of a T. M. modulator H6. Also included in the modulator H5 is a pair of electron discharge tubes H2 and H4 connected together in push-pull fashion, the grids of tubes H2 and H4 being fed from opposite ends of the split .secondary winding
  • the anode circuits of tubes H2 and lill are joined together at Il@ and the combined outputs of the tubes fed to a pulse clipper and Shaper H. Transformer
  • Fig. 4. is a transformer Esa which may be identical to the transformer 25 in Fig. 1.
  • the ends of the secondary winding -of transformer 28a are connected respectively to a second primary winding
  • the audio-signal representing the intelligence which it is desired to transmit is applied to the primaryv winding Vof transformer 28a in the same manner that'the audio-signal is applied to the primary winding of transformer 28 of Fig. l.
  • a masking signal 2 which may be identical to the masking signal of Fig. l is applied to-the center-tapped vsecondary of transformer 28asimilarly as shown in Fig. 1.
  • 29 are fed to anR. F. translator i351 and then transmitted from an antenna
  • the modulatorcircuit HD it will be understood that it amplies and, in effect, full-wave rectifies the wave
  • ⁇ Time modulation of the. ⁇ lcusperA wave is Aproduced by applying thev i pulses
  • the signal intelligence operates,.k in effect, to vary Athe wave .L02 relative. to its zero axis as regards the full-wave-rectication.
  • the'cusps are preferably clipped from the wave by a known clipper and shaper H8 and shaped to form a train4 of substantially narrowl width pulses .138.
  • the TM pulse output from modulator; :12e will be a train .of pulses similar to the pulse train
  • a T-M transmitting .system such as shown in Fig. 4
  • means must beprovided inthe vreceiver for demodulating these TM pulses.
  • Fig. 5 illustrates. a TM demodulatoriZa which may be incorporated inthe receiving cirlcuit of Fig. 3 to replace the pulse amplitudeE demodulating or iiltercircuits 82 and Bil.
  • The-odd TM pulses (such as the train of TM pulses '
  • Curve aofFig. 6 represents avshorttrain fof a substantially linearly increasing signal wave.
  • Curve b shows awave "
  • 48 is called a -fundamental wave because the period thereof corresponds tothe pulse cadence period between alternate pulses as indicated at T on curve aof Fig. 6.
  • 48 may be used for demodulation purposes, but an odd harmonic of the fundamental wave
  • 118, therefore.. is applied to a frequency multiplier
  • 56 is provided in the v.output of the frequency multiplier to shift the demodulating wave in phase ⁇ with respect. to .the. TM pulses.
  • 54 is. .applied directly to amixerunit
  • 38 are applied to the unit
  • the intelligence signals conveyed by the TM pulses are passed from the output
  • 54 is used as the demodulating wave
  • the tube is self-biased by a resistance-capacitance circuit
  • 10 is connected through coupling condenser
  • 16 is provided with a load resistor
  • the self-bias of the tube N56 is such that it will not respond to the input potential of the wave
  • the amplitude of the output pulses is increased.
  • the displacement modulation of the pulses is in directions away from each other the amplitude of the output pulses decreases.
  • This amplitude modulated pulse output provides a signal wave
  • a second TM demodulating circuit which is similar in all respects to the TM demodulating circuit 82a.
  • the output of this second demodulating circuit is fed through conductor 11 to switch 85.
  • a method of modulating a train of pulses of electrical potential comprising modulating a given characteristic of the odd pulses of said train with a given signal energy and modulating a like characteristic of the even pulses of said train with said given signal energy shifted in phase 180 from the signal energy applied to said odd pulses.
  • modulating operations of the odd and even pulses comprise varying the amplitude of the pulses according to the respectiveV modulating signal energy.
  • modulating operations of the odd and even pulses comprise displacing the sition according to the respective modulating signal energy.
  • a method of pulse modulation comprising pulses in time po- Y producing two series of pulses of electrical potential, the pulses of one series alternating with the pulses of the other series, modulating the pulses of said one series with signal energy, modulating the pulses of said other series with said signal energy displaced in phase substantially and combining the pulses of said two series into a single train of pulses.
  • a method of pulse modulation comprising producing two series of pulses of electrical p0- tential, the pulses of one series alternating with the pulses of the other series, modulating a given characteristic of the pulses of said one series according to a given signal energy, modulating said given characteristic of the pulses of said other series with said given signal energy shifted substantially 180 out of phase with the signal energy applied to said one series, and modulating said given characteristic of the pulses of both series with a further signal energy.
  • a method of private communication comprising generating two series of pulses of electrical potential, the pulses of one series alternating with the pulses of the other series, modulating a characteristic of the pulses of one series with a given signal energy, modulating a like characteristic of the pulses of the other series With said given signal energy shifted substantially 180 out of phase with the signal energy applied to said one series, combining the pulses of both series into a train, transmitting said train of pulses, receiving said train of pulses at a receiving point,
  • a method further including demodulating the pulses of the other of the two series, shifting in phase 180 the signal energy obtained from one of said two series, and combining the the signal energy obtained from the other of said two series.
  • a method of private communication comprising generating two series of pulses of electrical potential, the pulses of one series alternating in time with the pulses of the other series, modulating a given characteristic of the pulses of said one series according to a given signal energy, modulating said given characteristic of the pulses of said other series with said given signal energy shifted substantially 180 out of phase with the signal energy applied to said one series, modulating both series of pulses with a further signal energy, combining the pulses of both series into a single train, transmitting said train of pulses, receiving said train of pulses at a receiving point, separating the twoseries of pulses, demodulating to audio waves the pulses of the two series, shifting 180 in phase the audio wave derived from one of said series, combining said phase shifted audio wave with the other audio wave to cancel out said further signal, and reproducing the intelligence of said given signal energy from the combined audio wave.
  • a modulator system comprising means for producing a train of pulses of electrical potential, means to modulate a given characteristic of the odd pulses with a given signal energy, and means' to modulate said given characteristic of the even pulses with said given signal energy shifted in phase 180 from the signal energy applied to the odd pulses.
  • a pulse modulating system comprising means for producing two series of pulses of electrical potential, the pulses of one series alternating with the pulses of the other series, modulator means for the pulses of said one series, modulator means for the pulses of the other of said series, a source of signal energy, means to apply said signal energy at 180 difference in phase to the two modulator means, and means for combining th'e pulse output of the two modulator means into a single train of pulses.
  • said means for applying energy to said two modulator means includes means for applying a further 0 Number signal energy in phase to the two modulator means.
  • a private communication system comprising means for producing a train of pulses of electrical potential, means to modulate a given characteristic of the odd pulses with a given signal energy, means to modulate the even pulses withk said given signal energy shifted in phase from the signal energy applied to the odd pulses, means for transmitting the train of pulses thus modulated, means for receiving said train of pulses at a receiving point, means for separating the odd pulses from the even pulses, and means for demodulating one of the series of pulses from said separating means to reproduce said given signal energy.

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  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Radar, Positioning & Navigation (AREA)
  • Remote Sensing (AREA)
  • Digital Transmission Methods That Use Modulated Carrier Waves (AREA)
US531859A 1944-04-20 1944-04-20 Communication system Expired - Lifetime US2426225A (en)

Priority Applications (5)

Application Number Priority Date Filing Date Title
NL81626D NL81626C (en(2012)) 1944-04-20
BE479062D BE479062A (en(2012)) 1944-04-20
US531859A US2426225A (en) 1944-04-20 1944-04-20 Communication system
GB9320/45A GB591884A (en) 1944-04-20 1945-04-13 Pulse communication systems
FR951383D FR951383A (fr) 1944-04-20 1947-08-07 Systèmes électriques de communication

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Application Number Priority Date Filing Date Title
US531859A US2426225A (en) 1944-04-20 1944-04-20 Communication system

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US2426225A true US2426225A (en) 1947-08-26

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BE (1) BE479062A (en(2012))
FR (1) FR951383A (en(2012))
GB (1) GB591884A (en(2012))
NL (1) NL81626C (en(2012))

Cited By (25)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2509064A (en) * 1945-08-23 1950-05-23 Bell Telephone Labor Inc Reduction of noise in pulse position modulation systems
US2548796A (en) * 1947-06-02 1951-04-10 Rca Corp Double polarity pulse generator system
US2605410A (en) * 1946-08-27 1952-07-29 Rca Corp Pulse-time discriminator
US2607035A (en) * 1949-12-19 1952-08-12 Standard Telephones Cables Ltd Pulse multiplex transmission system
US2623952A (en) * 1950-04-01 1952-12-30 Magnetic Equipment Inc Modulating system
US2629053A (en) * 1948-03-15 1953-02-17 Phillips Petroleum Co Detonation meter calibrator
US2629857A (en) * 1946-08-10 1953-02-24 Int Standard Electric Corp Communication system utilizing constant amplitude pulses of opposite polarities
US2640151A (en) * 1949-07-14 1953-05-26 Westinghouse Electric Corp Blocking oscillator system
US2678425A (en) * 1950-02-21 1954-05-11 Raytheon Mfg Co Analogue computer
US2689344A (en) * 1951-05-15 1954-09-14 Stanley R Rich Pulse modulated speech transmission system
US2714704A (en) * 1951-03-23 1955-08-02 Rca Corp Quantizing modulation circuit arrangement
US2813151A (en) * 1953-10-06 1957-11-12 Bell Telephone Labor Inc Impulse signal distortion circuit
US2853634A (en) * 1954-01-05 1958-09-23 Westinghouse Electric Corp Saturable reactor keying for radio transmitters
US2855509A (en) * 1954-04-20 1958-10-07 Edward A Moore Variable delay time pulse generator
US2863999A (en) * 1953-04-21 1958-12-09 Rca Corp Wave shaper
US2864954A (en) * 1957-11-01 1958-12-16 Edward L Byrne Pulse regenerator circuit
US2866094A (en) * 1954-09-29 1958-12-23 Hoffman Electronics Corp Symmetrical to asymmetrical signal conversion circuit
US2880320A (en) * 1953-04-23 1959-03-31 Syrl K Ferguson Electronic message timing circuit
US2896501A (en) * 1953-05-28 1959-07-28 Faximile Inc Apparatus for outlining contours
US2961651A (en) * 1954-04-20 1960-11-22 Frank B Uphoff Synchronized system of interlaced scanning
US3008244A (en) * 1954-11-30 1961-11-14 Smith Meeker Engineering Compa Sonar simulator
US3095508A (en) * 1959-02-06 1963-06-25 Cons Electrodynamics Corp Alternating current power control system
US3384705A (en) * 1944-08-29 1968-05-21 Rosen Leo Facsimile privacy apparatus
US3603734A (en) * 1949-12-21 1971-09-07 Nat Defense Canada Secret signalling system
WO2002013436A1 (en) * 2000-08-09 2002-02-14 Avway.Com Inc. Method and system for steganographically embedding information bits in source signals

Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR768022A (fr) * 1933-01-18 1934-07-30 Procédé et appareil de communication électrique à haute fréquence assurant le secret de la correspondance et évitant les perturbations atmosphériques

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR768022A (fr) * 1933-01-18 1934-07-30 Procédé et appareil de communication électrique à haute fréquence assurant le secret de la correspondance et évitant les perturbations atmosphériques

Cited By (25)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3384705A (en) * 1944-08-29 1968-05-21 Rosen Leo Facsimile privacy apparatus
US2509064A (en) * 1945-08-23 1950-05-23 Bell Telephone Labor Inc Reduction of noise in pulse position modulation systems
US2629857A (en) * 1946-08-10 1953-02-24 Int Standard Electric Corp Communication system utilizing constant amplitude pulses of opposite polarities
US2605410A (en) * 1946-08-27 1952-07-29 Rca Corp Pulse-time discriminator
US2548796A (en) * 1947-06-02 1951-04-10 Rca Corp Double polarity pulse generator system
US2629053A (en) * 1948-03-15 1953-02-17 Phillips Petroleum Co Detonation meter calibrator
US2640151A (en) * 1949-07-14 1953-05-26 Westinghouse Electric Corp Blocking oscillator system
US2607035A (en) * 1949-12-19 1952-08-12 Standard Telephones Cables Ltd Pulse multiplex transmission system
US3603734A (en) * 1949-12-21 1971-09-07 Nat Defense Canada Secret signalling system
US2678425A (en) * 1950-02-21 1954-05-11 Raytheon Mfg Co Analogue computer
US2623952A (en) * 1950-04-01 1952-12-30 Magnetic Equipment Inc Modulating system
US2714704A (en) * 1951-03-23 1955-08-02 Rca Corp Quantizing modulation circuit arrangement
US2689344A (en) * 1951-05-15 1954-09-14 Stanley R Rich Pulse modulated speech transmission system
US2863999A (en) * 1953-04-21 1958-12-09 Rca Corp Wave shaper
US2880320A (en) * 1953-04-23 1959-03-31 Syrl K Ferguson Electronic message timing circuit
US2896501A (en) * 1953-05-28 1959-07-28 Faximile Inc Apparatus for outlining contours
US2813151A (en) * 1953-10-06 1957-11-12 Bell Telephone Labor Inc Impulse signal distortion circuit
US2853634A (en) * 1954-01-05 1958-09-23 Westinghouse Electric Corp Saturable reactor keying for radio transmitters
US2855509A (en) * 1954-04-20 1958-10-07 Edward A Moore Variable delay time pulse generator
US2961651A (en) * 1954-04-20 1960-11-22 Frank B Uphoff Synchronized system of interlaced scanning
US2866094A (en) * 1954-09-29 1958-12-23 Hoffman Electronics Corp Symmetrical to asymmetrical signal conversion circuit
US3008244A (en) * 1954-11-30 1961-11-14 Smith Meeker Engineering Compa Sonar simulator
US2864954A (en) * 1957-11-01 1958-12-16 Edward L Byrne Pulse regenerator circuit
US3095508A (en) * 1959-02-06 1963-06-25 Cons Electrodynamics Corp Alternating current power control system
WO2002013436A1 (en) * 2000-08-09 2002-02-14 Avway.Com Inc. Method and system for steganographically embedding information bits in source signals

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Publication number Publication date
NL81626C (en(2012))
FR951383A (fr) 1949-10-24
BE479062A (en(2012))
GB591884A (en) 1947-09-01

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