US2425066A - Pulsed multiplex system employing different width and repetition frequencies for each channel - Google Patents

Pulsed multiplex system employing different width and repetition frequencies for each channel Download PDF

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Publication number
US2425066A
US2425066A US579723A US57972345A US2425066A US 2425066 A US2425066 A US 2425066A US 579723 A US579723 A US 579723A US 57972345 A US57972345 A US 57972345A US 2425066 A US2425066 A US 2425066A
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United States
Prior art keywords
pulses
channel
pulse
channels
signal
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Expired - Lifetime
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US579723A
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English (en)
Inventor
Labin Emile
Donald D Grieg
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STC PLC
Federal Telephone and Radio Corp
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Standard Telephone and Cables PLC
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Application filed by Standard Telephone and Cables PLC filed Critical Standard Telephone and Cables PLC
Priority to US579723A priority Critical patent/US2425066A/en
Priority to GB28952/46A priority patent/GB623415A/en
Application granted granted Critical
Publication of US2425066A publication Critical patent/US2425066A/en
Priority to FR952462D priority patent/FR952462A/fr
Priority to ES182437A priority patent/ES182437A1/es
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04J—MULTIPLEX COMMUNICATION
    • H04J3/00—Time-division multiplex systems
    • H04J3/02—Details
    • H04J3/08—Intermediate station arrangements, e.g. for branching, for tapping-off
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B7/00—Radio transmission systems, i.e. using radiation field
    • H04B7/14—Relay systems
    • H04B7/15—Active relay systems
    • H04B7/155—Ground-based stations
    • H04B7/17—Ground-based stations employing pulse modulation, e.g. pulse code modulation

Definitions

  • This invention relates to 'transmission 'of' intelligence by radiant energy and to systems for broadcasting information and entertainment programs, such as sound, facsimile, picture, etc., in a multiplex method over the same or nearly the same carrier frequency.
  • Another object is to provide a ymethod and means for inserting in a given carrier medium a channel of signal pulses unsynchronized with the channel pulses already present in said medium, in a manner so that the signal pulses of the different channels may be separated at a receiving point With a minimum of interference from the inserted signal pulses.
  • Another object of the invention is to provide a system for transmitting or broadcasting a plurality of channels of intelligence ona common carrier Without synchronism between the different channels and means for unscrambling the pulses of the diierent channels at a receiving point with a minimum of interference from the pulses of channels overlapping the pulses of a desired channel.
  • the different channels of signal pulses may be produced at Widely diierent points Without any synchronizing connection and broadcast at a common carrier frequency at these points.
  • the signal pulses of ⁇ the different -channels ⁇ ,nof course, may be applied toa common transmission 2 medium sich 'as a wire line 'or coaxial cable at different peints therealong, either direct or in the forni of a modulated carrier of a common frequency. n,
  • the signal pulses of different channels are distinguished by differences in pulse Width and by greatly minimised by use of time modulation of thel pulses as distinguished from amplitude mod'- ul'ation.
  • the time modulation may take any one of the plurality of different forms.
  • the pulses ⁇ may be displaced in time relative to a given time position according to substantiall'y the instantaneous values of a signal wave or the successive pulses may be displaced toward and yati/'ay from 'each other in push-pull manner according to the modulating signal.
  • the pulsesqof a zgiven channel are unscrambled from the pulses of other channels, preferably vaccording to their 'distinguishing Width characteristic although other methods of separation may be employed.
  • the pulses ' may not only be separated according to Widtlfirfof the pulses but also by their average repetition rate ⁇ in onjunction With the Width distinguishing characteristic.
  • Fig. l is a diagrammatic illustration of a plu- 'rality of broadcasting stations and one receiver for selective reception according to the principles of our invention:
  • ⁇ 2 is a graphical illustration useful in explaining the selective' receiving function of the receiver of Figs. 1 and 5;
  • 3 is a lschematic Wiring and block diagram of the transmitting circuit of one of the broadcasting stations
  • Fig. 4 is a graphical illustration useful in eX- plainlng the operation 4of the pulse time modulator circuit shown Fig. 3;
  • Fig ⁇ 5 is a. block diagram of a receiver capable of selecting ⁇ any one of a plurality of signal channels broadcast simultaneously over a common carrier vfrequency 'according to the broadcasting arrangement of Fig'. 1;
  • Fig. 6 is1 a block diag-rain of a broadcasting systeinnfor' a pluralityv of signal czharinels; ⁇ and Fig'. *l is adiagrammatic illustration of a relay fr communicating system of the character to which our invention is applicable.
  • a plurality of transmitter stations I, 2 and 3 are shown for broadcasting on a common carrie-r frequency F1l and an additional transmitter station 4 for broadcasting intelligence on a carrier frequency F2.
  • a receiver 5 is also shown provided with two controls 6 and i for carrier frequency tuning and pulse width discrimination.
  • the signal pulses transmitted by stations I, 2 and 3 are distinguished in pulse Width and the average repetition Vrate of the pulses.
  • the signal pulses of station l are of a given width Wi and the average repetition rate is selected as R1.
  • the signal pulses of stations 2 and 3 are of diierent widths W2 and W3 and diiferent average repetition rates R2 and R3 respectively. Since transmitter station il operates on a carrier frequency diierent from the carrier frequency of stations I, 2 and 3, the signal pulses thereof need not distinguish from the pulses of stations I, 2 and 3 but may have the saine width and repetition characteristics as one of them.
  • graphs a, b and c show three trains of channel pulses A, B and C having different widths and repetition rates such as may be assigned to the transmitter stations I, 2 and 3 respectively. Since these signals may be transmitted simultaneously on a common carrier frequency F1, they will form a composite wave in the ether such as represented by graph d.
  • the pulses of these channels may be chosen of Various widths ranging from a fraction of one microsecond to two or more microseconds as may be desired.
  • a channel may have a pulse repetition rate anywhere from about 10,000 pulses per second to as high as 20,000 or more, but for other services the rate may be either higher or considerably lower than the 10,() rate mentioned above depending upon the type of intelligence transmitted.
  • the receiver of Fig. 1 which is shown in more detail in Fig. maybetuned to receive any desired carrier frequency such as Fi and may be further tuned for signal pulse selection according to pulse width.
  • the programs of the transmitter I, 2, 3 and 4 may be selectively received at 5 and, as described in greater detail hereinafter, with substantially no interference from the pulses of the channels not selected.
  • a transmitter is shown provided with one form of P. T. M. (pulse time modulator) 8, such as may be employed for production of signal pulses at a desired repetition rate and modulated in time according to the intelligence to be transmitted.
  • An oscillator 9 provides the basic wave for the modulator, the frequency of oscillation controlling the repetition rate of the pulses produced as will. be clear from the following description.
  • the base wave of oscillator 9 is represented at I0 o-n graph :I: of Fig. 4.
  • the wave I6 is applied to the primary II of an input transformer I2 in parallel with the signal voltage from audio source I3 which is applied to primary coil I4.
  • the modulator circuit includes two secondary coils I-5 and I6 coupled to the control grids of two vacuum tubes II and I8 in pushpull arrangement similar to a full wave rectier.
  • the modulator amplifies and, in eiect, fully rectifies the wave vIIB to obtain a cusper Wave 20, graph y of Fig. 4. While the rectication of wave Iii may be symmetrical with respect-to the zero e axis I9, it is shown for purposes of illustration as unsymmetrical by means of different biasing potentials 2l and 22, Fig. 3. This gives the effect of an offset axis 23, graph about which modulation takes place.
  • the signa-l intelligence operates, in effect, to vary the wave I0 relative to its offset axis 23 as respects the full wave rectication.
  • the maximum limits of relative variations between the wave and the axis 23 are indicated by the upper and lower modulation limits 24 and i9, the lower limit being in this instance selected the same as the original zero axis of wave I0.
  • the cusper wave 20 When the input signal varies the relative relation between the oiset axis 23 and the wave l to the upper limit 24, the cusper wave 20 is displaced as shown by the broken line 25, and when varied to the opposite limit I3, it is displaced as shown by broken line 26. It will be observed that the signal wave thus varies the time positions of the cusps 2l', 2B, 29 and 3! in push-pull manner toward and away from each other thereby decreasing and increasing the time intervals therebetween.
  • the cusps are clipped from the wave 2E) and shaped to form substantially rectangularly shaped pulses in pulse widthshaper 3i.
  • the Shaper 3I may be of any known type capable of clipping the wave 2i] between limits 32 and 33.r Since circuits of this character are well known a detailed showing is unnecessary.
  • may be repeated as shown in graph z, Fig. 4.
  • the pulses thus produced are used as the modulating voltage for an RF translator 34 for transmission at the chosen carrier frequency such as F1, for example.
  • Carrier frequency pulses are radiated by antenna 35.
  • the receiver 5 0f Fig. 1 is shown in greater detail.
  • the receiver includes an RF amplifier and detector 36 of broad band characteristics for receiving the train of pulses broadcast on a selected carrier frequency such as Fi.
  • the detector circuit should be sufliciently linear to preserve the pulse shapes upon detection even where there is considerable overlapping of the pulses as indicated lby the composite wave of graph d, Fig. 2.
  • the composite wave output of the detector is applied to a diiferentiator 3l of the character adapted to produce derivative pulses in response to each abrupt change in the leading and trailing edge portion of the wave. That is to say, for each change in the leading edge from an approximately steady voltage condition to a sharp voltage increase, a needle-like positive pulse is produced, and for each abrupt change in voltage from a substantially steady condition to a sharp decrease, a negative pulse of needle-like shape is produced.
  • Graph e represents the derivative pulses derived from differentiation of the composite wave form of graph d.
  • Differentiation of pulse 3S of channel A produces derivative pulses 38a and 38a the two derivative pulses corresponding in time to the leading and trailing edges of the pulse 38.
  • Differentiation of pulse 3S of channel C likewise produces derivative pulses 39e and 39e.
  • Differentiation of pulse which results from an overlapping of pulses from channels A and B produces positive derivative pulses im and tot corresponding to the abrupt changes in the leading edge of the pulse di), and negative derivative pulses lita and ilb' corresponding to the abrupt changes in the trailing edge of the pulse ll.
  • the composite pulses di, l2 and i3 when dierentiated produce positive derivative pulses die, da, 5l-2d, 42h, 43o-c and 33h and negative derivative pulses Mc', da', 52a', 212', A311', 153D', and 153e as shovm in graph e. It is clear that all of the derivative pulses of graph e correspond to leading and trailing edges of the channel pulses A1, A2, A3, A4, A5, B1, B2, B3, C1, C2 and C3 as shown by their time relation in graph a, b and c.
  • the output of clipper d5 may therefore be applied to any suitable T. M. demodulator 55 capable of translating the time displacement of the pulses into amplitude displacements which when passed through a low pass filter 56 may be applied to speaker 5l or other utilization apparatus.
  • the delay device i8 is adjusted to retard the inverted pulses an amount equal to W2
  • the width of the pulses of channel B the inverted pulses will have the timing indicated in graph i of Fig. 2.
  • the resultant may be represented by graph 7' wherein certain of the pulses coincide in the manner hereinbefore described.
  • the negative coincidence pulses 5e, 5i! and 50 are derived from pulses Mib and Z-dilh lb and 2-42b, A322 and 2l3b respectively of graphs e and z'.
  • pulses 39C of graph e and pulse 2-38a of graph i coincide to produce a coincidence pulse 6i of graph j.
  • This pulse however is of positive polarity as contrasted to the coincidence pulses resulting from the pulses of channel B and therefore is eliminated when the pulses of graph 7' are clipped at level 62, whereby pulses b1, b2, b3, etc., of graph k are obtained, which correspond exactly in the time relation of the channel pulses B1, Bz, B3, etc.
  • the receiver of Fig. 5 is capable of segregating the pulses of a given channel regardless of distortion due to the overlapping thereof by pulses of other channels. It is recognized that there may be occasional instances where a false pulse indication of the desired width may be produced by an overlapping relationship between pulses whereby a composite pulse is created having leading and trail'- ing edge portions corresponding to edges of the two pulses, spaced apart a time interval equal to the width of the desired pulse. The occurrence of such false indications, however, is very infrequent and moreover will as often as not occur at the proper time position for the modulating signal, and it can be stated that the receiver of Fig. 5 will unscramble the pulses and select substantially only the pulses of a desired Width regardless of distortion due to overlapping by ypulses of other channels.
  • pulse width selector circuits of the character shown in Fig. 5 reference may be had to the copending application of E. Labin. Serial No. 467,509, namelydvDecember 1, 1942, which is assigned to the Federal Telephone and Radio Corp.
  • Other pulse width discriminating circuits may, of course, be used for unscrarnbling the channel pulses.
  • Another such circuit is disclosed in a copending application of D. D. Grieg, Serial No. 511,404, filed November 23, 1943, and assigned to Federal Telephone and Radio Corp.
  • Fig. l shows the diiferent channels transmitted from different stations, it will be clear that the transmission may occur from a single station such as illustrated in Fig. 6.
  • the diierent channels may originate at studios located various distances from the broadcasting station. According to the principles of this invention such studios need not be synchronized, one with respect to the other, but may be permitted to have independent signal pulse repetition rates R1, R2 and R3 such as indicated for the pulse modulators E3, 64 and 55. rihese diierent rates, of course, will be controlled by the frequency of the oscillator associated with the modulator such as indicated at $5 for modulator E53.
  • the pulse widths for each channel are determined by the pulse Shaper -associated with the output of the modulator as indicated at 6l, 68 and 69 for the three channels.
  • the pulses lof ⁇ 7 each channel may thus be produced at the studio and transmitted by Wire or wireless to the main broadcasting station where they are mixed in a mixer circuit l and applied to an RF translator H for modulating a carrier of a given frequency.
  • Fig. 7 illustrates a further application of the principles of our invention.
  • the system shown comprises a series of relay stations l2, 13, M and 15, the stations 12 and l5 being shown as terminal or sub-terminal stations.
  • This system may comprise relays of the character adapted to transmit a multiple of channels on a common carrier freqency which is beamed from one repeater station to the next.
  • the signal pulses of the diierent channels may be timed to interleave, thereby forming a single train of pulses or they may be unsynchronized according to the transmitter arrangement of Fig. 6.
  • the rate of the signal pulses Will be difierent and also the Width thereof will be diiierent from the pulse rates and Widths of other channel pulses.
  • the pulses of the different channels may be unscrambled and the desired channel selected at receiving points as described in connection with the receiver of Fig. 5.
  • a method of simultaneously transmitting the intelligence of a plurality of sources comprising producing for each source of intelligence a train of electrical pulses of a Width and at a rate of recurrence different from the pulse Widths and recurrence rates of the pulses produced for the other of said sources, modulating in time a characteristic of the pulses oi each train according t-o substantially the instantaneous values of the corresponding source oI" intelligence, and transmitting the trains of pulses thus produced over a common transmission medium.
  • a method of simultaneously transmitting the intelligence of a plurality of sources at a given carrier frequency comprising producing for each source of intelligence a train of pulses of a Width and at a rate of recurrence different from the pulse widths and recurrence rates of the pulses produced for the other of said sources, modulating in time a characteristic of the pulses of each train according to substantially the instantaneous values of the corresponding source of intelligence, and amplitude modulating a carrier Wave of said given frequency according to the trains of pulses thus produced.
  • a method of simultaneously transmitting from a plurality of transmitting stations at a given carrier frequency for selective independent reception comprising producing at each station a. train of pulses of a Width and at a rate of recurrence different from the pulse Widths and recurrence rates of the pulses produced at the other of said stations, modulating in time a characteristic of the pulses of each train according to substantially the instantaneous value of an intelligence, and at each station, amplitude modulating a carrier wave of said given frequency according to the train of pulses produced for such station.
  • the method oi adding an additional channel of intelligence to said common carrier at any desired relay point along the chain of relay stations, comprising producing a train of signal pulses of a width and at a rate of recurrence different from the pulse Widths and recurrence rates of the 'signal pulses of the other channels, modulating a carrier of a frequency substantially the same as the frequency of said common carrier, and transmitting said carrier for reception by at least one of said relay stations, whereby said added channel of signal pulses is relayed by said stations on said common carrier.
  • pulse modulator means for the intelligence of each source including means for producing signal pulses of Width and average repetition rate diierent from the widths and repetition rates of the signal pulses produced for the other sources, means for transmitting the signal pulses of said sources over a common transmission medium, and means at a receiving point for receiving from said common transmission medium the signal pulses of a desired one of said sources according to the pulse width and average repetition rate characteristics of such channel.
  • a communication system having a plurality of sources of intelligence, pulse modulator means for the intelligence of each source including means for producing signal pulses of Width and average repetition rate different from the widths and repetition rates of the signal pulses produced for the other sources, and means for transmitting the signal pulses of said sources over a common transmission medium; and means at a receiving point for receiving the pulse Wave resulting from the signal pulses of said plurality of sources, means for differentiating the pulse wave to obtain a series of derivative pulses corresponding to abrupt changes in amplitude of said wave, the derivative pulses corresponding to changes increasing in amplitude being of a rst polarity and those corresponding to changes decreasing in amplitude being of a second polarity, means for producing selecting pulses disposed at a time interval equal to the Width of the pulses 0f a desired channel from the derivative pulses of one of said polarities, and means responsive to coincidence between a selecting pulse and a derivative pulse of the other of said polarities to produce an output pulse.
  • a systemior transmitting a plurality of channels of signal pulses on a common carrier over a chain of relay stations; means for adding an additional channel of intelligence to said comcarrier at any desired relay point along the chain of relay stations, comprising means for oducing a train of signal pulses of a Width and a rate of recurrence different from'the pulse Widths and recurrence rates of the signal pulses of the other channels, means for modulating a carrier oi a frequency substantially the same as the ircduency of said common carrier, and means lor transmitting said carrier for reception by at least one of said relay stations, whereby said added channel of signal pulses is relayed by said stations cn said common carrier.
  • means for transmitting a plurality of channels of signal pulses on a common carrier over a chain of relay stations comprising means for producing a train of signal pulses of a width and at a rate of recurrence difierentgfrom the pulse Widths and recurrence rates of the signal pulses ol the other channels, means lor modulating a carrier of a frequency substantially the same as t frequency of said common carrier, and means 12 sponding to the pulse envelope shapes of said carrier, and means for selectively obtaining from the pulse Wave pulse energy corresponding to the signa1 pulses of a desired channel to the exclu- 5 sion of the other signal pulses.

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  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Mobile Radio Communication Systems (AREA)
  • Digital Transmission Methods That Use Modulated Carrier Waves (AREA)
US579723A 1945-02-26 1945-02-26 Pulsed multiplex system employing different width and repetition frequencies for each channel Expired - Lifetime US2425066A (en)

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Application Number Priority Date Filing Date Title
US579723A US2425066A (en) 1945-02-26 1945-02-26 Pulsed multiplex system employing different width and repetition frequencies for each channel
GB28952/46A GB623415A (en) 1945-02-26 1946-09-27 Improvements in or relating to multichannel electric pulse communication systems
FR952462D FR952462A (fr) 1945-02-26 1947-08-07 Systèmes de transmission de communications
ES182437A ES182437A1 (es) 1945-02-26 1948-02-18 Un sistema múltiple de radiotransmisión

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US579723A US2425066A (en) 1945-02-26 1945-02-26 Pulsed multiplex system employing different width and repetition frequencies for each channel

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ES (1) ES182437A1 (fr)
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GB (1) GB623415A (fr)

Cited By (21)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2451347A (en) * 1947-01-17 1948-10-12 Clarence H Mcshan Frequency shift pulse time modulation
US2486100A (en) * 1944-05-05 1949-10-25 Automatic Elect Lab Voice frequency signaling circuits for telephone systems
US2524776A (en) * 1947-07-02 1950-10-10 Standard Telephones Cables Ltd Pulse time modulation repeater system
US2530081A (en) * 1947-03-28 1950-11-14 Karl F Ross Receiver for wave-length modulated electric waves
US2535547A (en) * 1946-09-10 1950-12-26 Rca Corp Telemetering system
US2552013A (en) * 1947-04-22 1951-05-08 Gen Railway Signal Co Pulse duration discriminator
US2556074A (en) * 1947-10-29 1951-06-05 Rca Corp Pulse width selection
US2563879A (en) * 1947-07-22 1951-08-14 Komnenus M Soukaras Time characteristic determination of recurrent signals
US2567203A (en) * 1946-02-05 1951-09-11 Marcel J E Golay Multiplex communication system utilizing successive, different pulse modulation techniques
US2640151A (en) * 1949-07-14 1953-05-26 Westinghouse Electric Corp Blocking oscillator system
US2676202A (en) * 1949-01-12 1954-04-20 Companhia Portuguesa Radio Mar Multichannel communication with varying impulse frequency
US2685044A (en) * 1948-02-05 1954-07-27 Rca Corp Quantizing tube
US2719188A (en) * 1950-05-05 1955-09-27 Bell Telephone Labor Inc Non-synchronous time division multiplex telephone transmission
US2890283A (en) * 1953-05-02 1959-06-09 Int Standard Electric Corp Repeating system for time-division multiplex communication circuits
US3117313A (en) * 1957-04-04 1964-01-07 Marconi Co Ltd Radar systems
US3160711A (en) * 1960-06-04 1964-12-08 Bell Telephone Labor Inc Nonsynchronous time-frequency multiplex transmission system
US3177488A (en) * 1959-12-24 1965-04-06 Bell Telephone Labor Inc Broad band microwave radio link
US3261919A (en) * 1961-12-01 1966-07-19 Bell Telephone Labor Inc Asynchronous pulse multiplexing
US3261920A (en) * 1961-12-01 1966-07-19 Bell Telephone Labor Inc Asynchronous pulse multiplexing
US4295221A (en) * 1977-04-28 1981-10-13 Stiftelsen Institute For Mikrovagsteknik Vid Tekniska Hogskolan I Stockholm Method and apparatus at one-way or two-way information link to effect interference suppression
US20090087189A1 (en) * 2007-09-28 2009-04-02 Rollins George E Non-interfering transmitted-beam pairs

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
None *

Cited By (22)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2486100A (en) * 1944-05-05 1949-10-25 Automatic Elect Lab Voice frequency signaling circuits for telephone systems
US2567203A (en) * 1946-02-05 1951-09-11 Marcel J E Golay Multiplex communication system utilizing successive, different pulse modulation techniques
US2535547A (en) * 1946-09-10 1950-12-26 Rca Corp Telemetering system
US2451347A (en) * 1947-01-17 1948-10-12 Clarence H Mcshan Frequency shift pulse time modulation
US2530081A (en) * 1947-03-28 1950-11-14 Karl F Ross Receiver for wave-length modulated electric waves
US2552013A (en) * 1947-04-22 1951-05-08 Gen Railway Signal Co Pulse duration discriminator
US2524776A (en) * 1947-07-02 1950-10-10 Standard Telephones Cables Ltd Pulse time modulation repeater system
US2563879A (en) * 1947-07-22 1951-08-14 Komnenus M Soukaras Time characteristic determination of recurrent signals
US2556074A (en) * 1947-10-29 1951-06-05 Rca Corp Pulse width selection
US2685044A (en) * 1948-02-05 1954-07-27 Rca Corp Quantizing tube
US2676202A (en) * 1949-01-12 1954-04-20 Companhia Portuguesa Radio Mar Multichannel communication with varying impulse frequency
US2640151A (en) * 1949-07-14 1953-05-26 Westinghouse Electric Corp Blocking oscillator system
US2719188A (en) * 1950-05-05 1955-09-27 Bell Telephone Labor Inc Non-synchronous time division multiplex telephone transmission
US2890283A (en) * 1953-05-02 1959-06-09 Int Standard Electric Corp Repeating system for time-division multiplex communication circuits
US3117313A (en) * 1957-04-04 1964-01-07 Marconi Co Ltd Radar systems
US3177488A (en) * 1959-12-24 1965-04-06 Bell Telephone Labor Inc Broad band microwave radio link
US3160711A (en) * 1960-06-04 1964-12-08 Bell Telephone Labor Inc Nonsynchronous time-frequency multiplex transmission system
US3261919A (en) * 1961-12-01 1966-07-19 Bell Telephone Labor Inc Asynchronous pulse multiplexing
US3261920A (en) * 1961-12-01 1966-07-19 Bell Telephone Labor Inc Asynchronous pulse multiplexing
US4295221A (en) * 1977-04-28 1981-10-13 Stiftelsen Institute For Mikrovagsteknik Vid Tekniska Hogskolan I Stockholm Method and apparatus at one-way or two-way information link to effect interference suppression
US20090087189A1 (en) * 2007-09-28 2009-04-02 Rollins George E Non-interfering transmitted-beam pairs
US7912376B2 (en) * 2007-09-28 2011-03-22 Rockwell Automation Technologies, Inc. Non-interfering transmitted-beam pairs

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FR952462A (fr) 1949-11-17
GB623415A (en) 1949-05-17
ES182437A1 (es) 1948-04-16

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