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US2489302A - Multichannel time modulated electrical pulse communication system - Google Patents

Multichannel time modulated electrical pulse communication system Download PDF

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Publication number
US2489302A
US2489302A US602804A US60280445A US2489302A US 2489302 A US2489302 A US 2489302A US 602804 A US602804 A US 602804A US 60280445 A US60280445 A US 60280445A US 2489302 A US2489302 A US 2489302A
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Prior art keywords
pulses
pulse
channel
time
valve
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US602804A
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Levy Maurice Moise
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International Standard Electric Corp
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International Standard Electric Corp
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04J—MULTIPLEX COMMUNICATION
    • H04J3/00—Time-division multiplex systems
    • H04J3/02—Details
    • H04J3/04—Distributors combined with modulators or demodulators
    • H04J3/042—Distributors with electron or gas discharge tubes
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03K—PULSE TECHNIQUE
    • H03K17/00—Electronic switching or gating, i.e. not by contact-making and –breaking
    • H03K17/51—Electronic switching or gating, i.e. not by contact-making and –breaking characterised by the components used
    • H03K17/54—Electronic switching or gating, i.e. not by contact-making and –breaking characterised by the components used by the use, as active elements of vacuum tubes
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03K—PULSE TECHNIQUE
    • H03K7/00—Modulating pulses with a continuously-variable modulating signal
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03K—PULSE TECHNIQUE
    • H03K9/00—Demodulating pulses which have been modulated with a continuously-variable signal
    • H03K9/04—Demodulating pulses which have been modulated with a continuously-variable signal of position-modulated pulses

Definitions

  • the present invention relates to multi-channel electrical pulse communication systems.
  • each channel is allotted its respective portion of a cycle period during which the channel is made alive and the intelligence of the channel is transmitted as the time modulation of a pulse, for example the pulses of a channel are time phased between predetermined time limits, in accordance with the instantaneous amplitude of the signal wave of that channel.
  • Arrangements for successively and cylically bringing the channels into use or making them alive are known as distributors, there being normally a distributor at the transmitter and a distributor at the receiver working in synchronism.
  • the distributor functions as a channel selector.
  • the whole of a channel period should not be of any greater duration than the limits of modulation oi the time modulated pulses, and thus the channel period coincides with the channel modulation limits, which in general will be the same for all channels of a system.
  • the whole of the distributor cyclic period shall be occupied by channels substantially no time period is usually allowed between the termination of one channel period and the commencement of the next.
  • an essential factor of the system is that no two adjacent channels should overlap in'time, otherwise cross talk or other interferences between the channels may result. It is the chief object of this invention to eliminate cross talk due to the overlapping in time of adjacent channels and to provide a multi-channel pulse communication system in which the period allotted to a channel does not commence until the preceding channel period has terminated.
  • This object is attained in accordance with the present invention by utilising pulses of rectangular wave form whose duration determines the duration of the portion of the distributor cyclic period constituting a channel period and oncetively adding to these pulses concurrently occurring pulses of another train of pulses having a smooth amplitude variation in phase with the rectangular pulses, one of the trains of pulses being derived from the distributor, and applying the addition resultant wave of a channel together with the intelligence wave of that channel to a pulse generator to produce time modulated pulses in accordance with the varying amplitude of said intelligence wave.
  • the pulse generator may comprise electron discharge tubes, for example as in and decreases from a maximum to a minimum or vice versa during a channel period.
  • Suitable wave forms are, for example, a saw-tooth wave form, a' triangular wave form or sinusoidal wave form.
  • the wave form should be linear, since a non-linear wave form introduces distortion unless special precautions are taken.
  • Either the rectangular wave form pulse or the auxiliary pulse is obtained from the distributor system.
  • One way of obtaining the time modulated pulses is by allowing varying portions of the crest of the resulting combined wave form to pass to the circuits of the channels in accordance with the instantaneous amplitudes of the signal waves of the respective channels. The portion of the crest of the wave passed in the circuit may then be utilised in any desired manner to produce the desired type of time modulation pulses.
  • the crest portions may be greatly amplified and amplitude limited to produce duration modulated pulses, or the crest portions of the linear wave forms may be applied to a. difierentiating circuit to produce time-phased pulses, single or double push-pull pulses being obtained, depending upon whether a saw-tooth or triangular auxiliary wave form is originally employed.
  • the apparatus used for passing the crest of the resulting combined wave form may be, for example, an electron discharge tube type of amplifier steadily biassed at the potential of the mid-amplitude of the auxiliary portion of the combined wave form, the bias or cut-off potential of the tube being varied in accordance with the amplitude of the signal wave to be transmitted.
  • the amplitude of the sig nal wave may possibly be so negative at times as to neutralise the amplitude of the positive resulting combined wave, so that no portion of the crest of the combined wave is passed through the circuit and no pulse will be transmitted in the system corresponding to the particular amplitude of the signal wave resulting in this state of affairs.
  • a similar state of affairs may exist, utilising a negative resulting combined wave and the positive signal maximum.
  • Such a missing pulse may have serious repercussions at the transmitof constant duration herein called a "Safeguard pulse is superimposed on the maximum of the combined wave form applied to the modulator at the end of said combined waveform so that such short pulse will at least be transmitted.
  • a device may be used to limit the signal amplitude to within predetermined operational limits.
  • each channel pulse is produced by triggering a multi-vibrator type of circuit at suitable intervals oftime, and the triggering is effected by a combined wave of trapezoidal form produced by superimposing a saw-tooth wave form on a rectangular wave form.
  • the triggering voltage of the multi-vibrator is arranged to be the mean of the trapezoidal wave form and is varied by application of the sig.. nal wave to the multi-vibrator so that the point of triggering on the trapezoidal wave form is advanced or retarded in accordance with the instantaneous positive or negative amplitude of the signal Wave.
  • a multi-vibrator circuit In utilising a multi-vibrator circuit, if it is not triggered periodically, and in all pulse circuits, care must be taken to avoid production of any irregular bias voltages due to the irregular accumulation of charges or to ensure that no varying bias is produced by irregular charge at the end of each period. Such conditions might exist when, as hereinbefore explained, triggering fails because the signal amplitude is too great and neutralises the trapezoidal amplitude. Hence either a safeguard pulse is added to the maximum of the trapezoidal wave form or is applied on each multi-vibrator circuit or the signal amplitude is limited.
  • a safeguard pulse may be conveniently obtained by passing the current from the electron discharge device used for producing the trapezoidal wave form through an inductance and adding the voltage produced across the inductance to the trapezoidal wave.
  • One convenient form of circuit for producing waves of trapezoidal form comprises an electron discharge device having in its anode-cathode circuit a series-connected resistance-capacity combination and a by-pass impedance such as a resistance of high value. Rectangular pulses are applied to the input circuit of the device through a very large resistance. By biassing the grid or cathode of the device, it will limit the pulse amplitude and a constant current will appear between anode and cathode for the pulse duration and the condenser will gradually charge up providing an increasing voltage across the resistance capacity combination.
  • the shunt resistance provides a discharge path for the condenser during the intervals between pulses.
  • the rectangular pulses for application to the electron discharge device may be obtained from a passive delay network or artificial line used as a distributor in a multi-channel system.
  • a trapezoidal wave form obtained by the use of a resistance capacity network introduces distorting components into the transmitted time modulated pulses on account of the fact that the increase of voltage across the network with time between the time limits of the wave form, is not linear but varies exponentially.
  • this distortion is neutralised at the receiver by utilizing a demodulator which produces duration modulated pulses under the control of the received time modulated pulses and involving a resistance capacity network whose time constant is substantially equal to the time constant of the resistance-capacity network at the transmitter.
  • the invention also provides an electrical communication system in which the intelligence wave is transmitted as a time modulation of a series of electrical pulses and having at the transmitter a modulator arrangement for producing time modulated pulses in accordance with the instantaneous amplitude of the intelligence wave and involving the time constant of an impedance network, e. g.
  • the demodulator comprises an arrangement for producing under the control of the received pulses duration modulated pulses whose voltage varies with time in an exponential manner according to the same exponent as the variation at the transmitter. If a resistancecapacity network is employed at the transmitter in the modulator and at the receiver in the demodulator the time constants of the two networks accordingly are the same.
  • Fig. 1 shows the transmitter of a multi-channel system with the circuit arrangement of a modulator embodying the invention in detail.
  • Fig. 2 shows several curveswhich will be used in the description of the operation of Figure 1.
  • Figs. 3, 4 and 5 are graphs showing harmonic content in a distorted pulse and referred to in the description.
  • Fig. 6 shows the circuit of another form of trapezoidal wave form generator.
  • Fig. 7 is an explanatory diagram.
  • Figs. 8a, 10a and 101 are alternative networks for use in producing trapezoidal type of wave forms having exponential variation with time.
  • Fig. 8b shows the wave form produced by the network of Fig. 8a.
  • Fig. 9 is a circuit diagram of another modulator embodying the invention. a
  • Fig. 11 is a circuit diagram of a demodulator embodying the invention.
  • Fig. 12a is the equivalent network of the network in Fig. 11 producing the trapezoidal type of wave form having exponential variation with time. 1
  • Fig. 12b shows the duration modulated pulse with the exponential wave form produced by network shown in Figure 12a.
  • Fig. 13 shows an alternative circuit arrangement of demodulator for producing duration modulated pulses having exponential waveform.
  • Figure 1 shows diagrammatically the transmitting end of a multichannel electrical pulse communication system in which the intelligence wave of each channel is transmitted as a time phase modulation of a series of electrical pulses, and utilising as a distributor a passive delay network or artificial line indicated generally at I.
  • a master pulse generator indicated by the block 2 may be of any known type of generator of pulses of rectangular wave form as indicated at 3. These pulses of rectangular wave form are fed to the input terminals of the delay network or artificial line i, and as synchronising pulses through a one way device t to a transmission line 5 where they are combined with the trains from the channels and passed to a carrier frequency modulator for transmission through the desired medium.
  • the delay network comprises a plurality of series connected cells, all alike and each com prising inductances and capacities and may he resistances and so designed to delay a current passed therethrough by equal intervals or time.
  • Channel selector pulses of rectangular wave form are obtained from respective tapping points equally spaced along the network l as indicated at ti, ll, 9, 9 and u.
  • the duration of the rectangular pulse 3 is made equal to the channel period and hence equal to the time delay produced between any two successive points on the delay network I.
  • This equipment comprises a pulse generator US which is shown in the form of a multivibrator consisting of two valves ill, it interconnected in well known manner and designed to'be blocked by a suitable negative bias until it strikes by the application of the combined rectangular wave and auxiliary wave together with the intelligence wave applied to the control grid 19 of valve H.
  • a pulse of trapezoidal wave form is employed as the equivalent of the combination of a rectangular pulse and a pulse of sawtooth waveform.
  • the means for producing the trapezoidal waveform comprises an electron discharge valve Zll to the control grid of which rectangular pulses as shown at 2! obtained from tapping point 11 of the distributor delay network are applied and has in its anode-cathode circuit a network comprising a ing edge t coincides with the limit TLZ.
  • a positive trapezoidal wave may be obtained from the cathode of valve 20.
  • the network 22, 23 and 24 is connected in the anode circuit instead of the cathode circuit as shown.
  • the trapezoidal waveform and the intelligence wave, obtained for example from a microphone 25 are applied addi tively, through condenser 26 and resistance 21 respectively to the control grid IQ of valve ll of the m'ultivibrator I6. It will be observed that resistances 2'! and 28 and the microphone 25 are in series in the grid circuit of valve IT.
  • a saturated inductance coil 29 is included in the anode circuit of valve 20 for the purpose of producing the safeguard pulse at the end of the trapezoidal waveform.
  • This coil 29 acts as a differentiating circuit to the current pulse of rectangular waveform passing through the valve on account of the pulse 21. on the control grid.
  • a positive pulse is required at the end of the rectangular pulse.
  • the short pulse obtained at the end of the rectangular pulse is positive and is assumed to be applied through condenser .30 to a grid of valve ll for simplicity.
  • a one way device Si is provided to eliminate the negative pulse, if necessary.
  • Pulses of trapezoidal waveform are thus applied to the control grid ill of valve ll and the control grid 32 of valve it is biassed by means or a potentiometer so that the multivibrator triggers when the voltage on control grid ill is that represented by the mid-point of the trapezoidal waveform when applied alone to ill.
  • Pulses as indicated at ti l whose duration depend up the time constants of the multivibrator circuit and which is arranged to have an on period shorter, equal or longer than the duration of a trapezoidal pulse. are obtained from across the resistance Ill-ii in the cathode circuit of valve it. These pulses are of positive sign, but if pulses of negative sign are required, they may be ob The trailing edges of these pulses may occur after the termination of a channel period and hence, a short sharp pulse marking the leading edge which is time phase modulated is obtained by difierentiating the longer pulses at by means of the capacity .th and resistance tl.
  • the positive and negative pairs of pulses as represented at it are produced and the negative trailing pulse is eliminated by means of a diode til and the positive pulse is applied to the transmission conductor 5 viav a diode it to combine it with the pulses from the other channel equipments.
  • the diode M serves to isolate the channel equipments from each other. As indicated in. the drawing the output of each channel equipment is fed to the line 5 through a diode.
  • Curve a shows the synchronising pulses S fed to line 5 and the mean positions in time of the channel pulses of the respective channels are indicated by the arrows CH9 CH6.
  • the pulses may 00- cupy any position within the time limits represented by the dotted lines.
  • the pulse CHl may occupy any position between the time limits represented by lines TLl and TLZ.
  • Curve b shows the rectangular pulse Whose leading edge I coincides with the limit TM and whose trail- The duration of the rectangular pulse thus defines the channel period.
  • Curve shows a pulse of sawtooth waveform whose duration is equal to the duration of the rectangular pulse bl. This, however, is not necessary, the pulse cl may have a greater duration as shown in broken lines c.
  • Curve d shows the resultant pulse after adding pulses bl and cl.
  • the broken line d shows the resultant pulse after adding pulses bl and c. It will be observed that the leading and trailing edges of the rectangular pulse still define the channel period.
  • Curve e shows the pulse d2, similar to dl, for channel 2. It will be understood that similar pulses occur at successive periods for the remaining channels.
  • Curve I shows the trapezoidal waveform produced by the network 22, 23, 24 in the cathode circuit of valve 20, Fig. 1.
  • the rectangular pulses for example bl, Fig. 2, obtained from the distributor delay network 1, Fig. l, are applied to the control grid of valve 20 through a resistance ll of very high value, and constant current will flow between anode and cathode for the pulse duration.
  • the capacity 22 gradually charges up, providing an increasing voltage at the cathode of valve 20 as indicated by the line 42 in curve I, Fig. 2.
  • the leading edge bi is produced by the current flow through resistance 23 due to the leading edge of the rectangular pulse.
  • Curve 9 shows a similar trapezoidal pulse T2 for channel 2.
  • the bias on the grid of valve I8 is adjusted so that the multivibrator will trigger when the voltage on control grid IQ of valve l'l attains a predetermined-value which is equal to the mean value of the trapezoidal pulse.
  • This value is represented in curves d-g, Fig. 2, by the broken line TV.
  • the intelligence wave is applied to the valve I'I additively in series with the pulse, so that efiectively the trapezoidal pulse is raised or lowered with respect to the voltage level TV. In other words, the voltage level TV moves with respect to the pulse between the limits TV! and TV2.
  • the points where these lines TVI, TV, TV2 cut the pulse as shown in curvej represent the triggering moments of the multivibrator l6.
  • Curve h represents the pulse obtained from the resistance 35 in the cathode circuit of valve ll of multivibrator IS.
  • the instantaneous amplitude of the intelligence wave of channel i is assumed to raise the pulse Tl curve I, so that the multivibrator is triggered when the trapezoidal pulse passes through the voltage value represented by point 111.
  • the multivibrator triggers 8 and produces the leading edge of pulse 4H whose duration depends upon the constants of the multivibrator.
  • the intelligence wave amplitude raises or lowers the trapezoidal pulse, for example, so as to trigger the multivibrator at the point 112 (curve Dto produce the pulse 2H curve h.
  • the pulses IH and 2H are assumed tobe of the same duration, but it will be observed that the leading edges are moved with respect to the mean pulse positions represented by the arrows CHI.
  • Curve It shows the pairs of positive and negative pulses IKP, IKN, 2K? and 2KN obtained by differentiating the pulses IHI and 2H! respectively by the capacity 26 and resistance 31, Fig. 1.
  • Curve kp shows the train of positive pulses IKP, 2KP'after eliminating the negative pulses by means of diode 39. Since IX? and 2K? are produced from the leading edges of pulses .IHI and 2Hl which are time phase modulated, the train of pulses IKP, 2KP are also time phase modulated.
  • the method of modulating just described is well known but usually a sawtooth wave form is used in place of the trapezoidal waveform.
  • the trapezoidal waveform, or other waveform having waveform with perpendicular leading and trailling edges has the advantage that the channel pulses are modulated in time within the period determined by the leading and trailing edges and cannot go beyond them providing the amplitude of these edges is great enough.
  • the time-phase modulated pulses are converted by means of known buildback circuits into duration modulated pulses which are passed through a low pass filter to produce the intelligence wave.
  • This method of demodulation introduces no amplitude distortion provided the cut-off frequency is lower than fe/2, where f. is the channel pulse repetition frequency or the distributor cyclic frequency.
  • f. is the channel pulse repetition frequency or the distributor cyclic frequency.
  • a very small amplitude distortion appears at submultiple frequencies of jg, but these distortions are usually very small of the order of 2.0% for Iii/3, .0496 for fe/4 and completely negligible for the other subharmonics.
  • Figs. 3, 4 and 5 give numerical values for the harmonic distortion produced respectively by the modulation process employing a trapezoidal waveform as hereinbefore described, (Fig. 3), the demodulation process, (Fig. 4) and the overall distortion produced by the modulation process followed by the demodulation process (Fig. 5).
  • the abscissae represent X0 for full modulation. It will be observed that the modulation and the demodulation processes taken individually produce an appreciable and similar amount of second harmonic. Fortunately the second harmonic components introduced at the two stages are of opposite signs, so that the second harmonic distortion produced at modulation tends to neutralise the distortions produced at demodulation. This fact explains why the second harmonic present in a wave after the modulation and demodulation processes has a relatively small amplitude, especially for small values of X0.
  • the third harmonic component introduced at the stages has the same sign at the modulation stage as at thedemodulation stage so that the third harmonic amplitude after demodulation is greater than the amplitude of third harmonic component introduced at either stage. this increase in distortion for small values of X0.
  • harmonic distortion may occur.
  • the pulses are never perfect because they are built by means of valves and networks. If the circuit is suitably designed the distortion produced by the valves can be reduced to a very small percentage since in pulse technique the valves work mainly as relays below cut-oil or at full saturation, but the networks have time constants and the pulses are distorted by passing through them. In many cases the design of distortionless circuits presents some important disadvantages and in others the distortion is considerable and unavoidable.
  • This feature of the invention is not limited to modulators using trapezoidal waveform and demodulators using gating pulses of rectangular waveform but may be applied in all cases where a time modulation is produced under the control of an arrangement involving the time constant of a resistance capacity or resistance inductance combination and to demodulators controlled by an arrangement involving the time constant of a resistance-capacity or resistance inductance combination.
  • a modified form of trapezoid pulse generator is shown, and may be arranged to feed pulses of trapezoidal waveform to a modulator as hereinbefore described in relation to Fig. 1.
  • the arrangement in Fig. 6 only differs from the arrangement 22, 23, 24 shown in Fig. 1 in that a further resistance 43 completes a chain of resistances with 23' and 24' across the H. T. supply to enable a bias to be obtained on the cathode.
  • Pulses as indicated at M are obtained from a point on the distributor network to bring the channel cyclically into use. These pulses are herein called selector pulses and as explained in my co-pending United States application, Serial No. 602,803, filed July 2, 1945, for Multi-cl'iannel electrical pulse communication systems, now Patent No. 2,462,111, issued Feb. 22, 1949, are more or less distorted and consequently produce very distorted trapezoid pulses in the output circuit of valve cautions are taken. If the amplitude of the selector pulses 44 is very great grid current will pass in valve 20' and the anode current in valve 20' will remain nearly constant until the selector pulse disappears.
  • Formula 6 shows that the second harmonic distortion at modulation is smaller than if T is smaller than 1% of the time constant RC. Assume a modulation depth equal to 2.5 microseconds, this means that RC must be greater than 250 microseconds. For a repetition frequency of kc./s, this means that RC must be much greater than the repetition period.
  • valve 20 determines at what voltage value in the amplitude of the selector pulse, the valve will begin to pass current.
  • said bias determines the lower limit of the slice cut, so to speak, by the valve 26 on the applied selector pulses as indicated by the broken lines 41 and 48, Fig. '7, 48 representing the saturation voltage of valve 20.
  • the value of this lower limitin line 41 must have a value which is a function of the shape and amplitude of the selector pulses as is explained in the aforementioned United States application Ser. No. 602,803.
  • the bias voltage of valve 20 is of the same order of value as the increase of voltage during the build-up of the trapezoid pulses. It is clear that since the bias voltage has to obey two very different requirements, only a compromise is possible.
  • variable duration pulse wave form obtained at demodulation must have the portion between the leading and trailing edges substantially linear and parallel to the time axis. This condition however is not fulfilled in most types of demodulator circuits, so choice of demodulator circuits is limited.
  • the grid current appearing at the modulator multivibrator is of the order of 3 milliamps and if the modulator triggers at the middle amplitude voltage of the trapezoid pulse, the discharge due to the grid .current will result in a reduction of about 5% of the build up voltage and a great portion of this voltage will affect the height of the next trapezoid pulse thus shifting the position in time or time phase of the corresponding channel pulse in a multi-channel system as well as producing a harmonic distortion.
  • the voltage swing of the cathode is equal to the voltage amplitude of the trapezoid pulses and may be very great, for instance, of the order of volts.
  • the trapezoid pulses obtained in 52, 53, 54 are negative and are applied-to the cathode 56 of the first valve 51 shown as a pentode of the modulator multivibrator 58, and the modulating signal is applied for simplicity on one of the grids of valve 51 as indicated diagrammatically at 59 by a microphone in series with the feedback from the output valve 60.
  • An amplifying valve BI is inserted between the input and output valves 51 and 60 of the multivibrator circuit.
  • variable duration pulses obtained in the demodulation process have the shape of an exponential curve between the .leading and trailing edges of the pulses, said exponential curve having the same exponent as the exponential part of the trapezoidal portion of the modulator at the transmitter.
  • the channel pulse will be shifted from its normal position by T microseconds when T is proportional to V.
  • the receiver the demodulator pulse will increase its width by T microseconds, and the amount of current supplied by the pulse to the low-pass filter will be equal to a constant plus an amount proportional to T, that is to say, to V.
  • J A.dT M+NV 7 where M and N are constants.
  • the plate current variation is, however, small andof the order of less than of I. This variation may be compensated for by varying the time constant RC at the receiver slightly from the theoretical value, to balance as nearly as possible other variations at the transmitter and receiver. resulting from the plate current variation at the transmitter.
  • Fig. 11 shows a gating pulse generator valve H connected to a demodulator multivibrator comprising valves 12, 13, I4.
  • This circuit is very similar to the modulator shown in Fig. 9.
  • , Fig. 11 corresponds to valve 50, Fig. 9, and feeds the capacity resistance network 15, 16, 11 in the cathode circuit of valve 72 to produce the exponential waveform.
  • the valve H is fed with pulses of rectangular waveform, as indicated at 18, for example, from a distributor delay network as herein fore mentioned.
  • Fig. 12a shows the circuit equivalent of network l5, 116, I1 and bearing in mind that the pulse produced in the anode circuit resistance and applied to the circuit 15, 16, I1 is negative the pulse produced across resistance 75 will be as shown in Fig. 12b.
  • Such a pulse is applied to the cathode circuit of the multibrator valve 12 which triggers the voltage represented by point 19 and the pulse is terminated at that point.
  • the channel pulses are applied on a grid of valve 14 numeral all denotes the leading edge of the pulse or commencement of the ,gate" period, 3
  • This point 19 can occur at any time between the time limits represented by and 82. It will be clear that the shape of the waveform of the gating pulse between the limits so and 82 is an exponential curve with a time constant equal to Cl? (Rl5'+R76'). If this time constant is equal to the time constant at the transmitter, for example C53 (RM-PR5! Figs!) the distortion will be minimum.
  • Figure 13 shows a type of demodulator utilising gas-filled valves producing the sametype of pulses as shown in Figure 12?).
  • This demodulator comprises two gas discharge valves 83 and 8G.
  • the capacity 85 charges up from the H. T. supply during the interval between pulses.
  • Selector pulses are applied to the grid of valve 83 as indicated at 86 and cause this valve to ignite and provide a discharge path for only be ignited when 83 is operated.
  • the channel pulses are applied to the control grid of valve 8
  • the pulse obtained at the terminal 88 is thus represented by the shaded portion of Figure 12b.
  • resistance 81 and capacity 85 can be adjusted at the receiver to eliminate the greatest amount of distortion.
  • a multi-channel electrical communication system comprising a distributor arrangement including a delay network, means for feeding to the input terminals of said network pulses of rectangular waveform, and means for obtaining chanel selector pulses of trapezoidal waveform of duration equal to a channel period from successive points along said network, and means for applying a trapezoidal pulse and the intelligence wave of a channel to a pulse generator to produce time modulated pulses in accordance with the varying amplitude of said intelligence wave.
  • a multi-channel electrical communication I system in which the intelligence wave of each channel is transmitted as a time modulation of a series of electrical pulses comprising a distributor arrangement including means for delivering channel selector pulses of rectangular waveform, means for deriving from said selector pulses, pulses of trapezoidal waveform, a pulse generator of the electron discharge type, and means for 241- plying said trapezoidal waveform and the intelligence wave of the channel to said/pulse generator to produce time modulated pulses.
  • said means for producing a trapezoidal waveform comprising a resistance-capacity network in which said capacity is shunted by a resistance, means for feeding said rectangular selector pulse to said network and means for taking said trapezoidal waveform from across said capacity in series with a resistance.
  • a multi-channel system as claimed in preceding claim 2 comprising means for superimposarrangement for rendering said channels operative cyclically and successively having a delay device fed at the input terminals with pulses of rectangular waveform, and means for each channel for producing from pulses of rectangular waveform pulses of'trapezoidal waveform means for applying pulses obtained at successive points along said device to respective ones of said trapezoidal waveform generators, a pulse generator for each channel and means for applying the trapezoidal waveforms and the intelligence waves of the channels to respective pulse generators to produce time modulated pulses.
  • a system as claimed in claim 5, said generator of pulses of trapezoidal waveform comprising a resistance-capacity network.
  • a multi-channel system as claimed in claim 5 further comprising means for applying at the end of each channel period a safeguard pulse of sufficient amplitude to operate said pulse generator in the event of reduction by the intelligence waves of the amplitude of the combined rectangular and other waveform or trapezoidal waveform, below the effective operating value.
  • a multi-channel electrical communication system in which the intelligence wave of each channel is transmitted as a time modulation-of a series of electrical pulses comprising a distributor arrangement providing time phased pulses of rectangular waveform for rendering said channels cyclically and successively operative, a pulse generator of the mutlivibrator circuit type for each channel, an electron discharge valve amplifier for ing substantially at the end of the trapezoidal I pulses a short sharp pulse of sumcient amplitude to affect the modulator to safeguard against possible neutralising of said trapezoidal pulses by the channel intelligence wave.
  • a multi-channel electrical communication system in which the intelligence wave of each channel is transmitted as a time modulation of a series of electrical pulses comprising a distributor each channel, a resistance-capacity network for the production of trapezoidal waveforms in the cathode circuit of one of the valves of said multivibrator circuit, means for feeding said amplifier with said rectangular pulses from said distributor arrangement, means for feeding the rectangular pulses from the anode-cathode circuit of said amplifier to said network and means for applying the intelligence waves of the channels to respective multivibrator circuits to control the instants of triggering of said multivibrator circuits in accordance with the instantaneous amplitudes of said intelligence waves to produce time modulated pulses.
  • a multi-channel electrical communication system as claimed in claim 5 further comprising means for eliminating effects due to distortion of the trapezoidal waveform, having an exponential variation of voltage or current with time.
  • a mvulti-channel electrical communication system as claimed in claim 5 further comprising means for eliminating effects due to distortion of the trapezoidal waveform having an exponential variation of voltage or current with time, including means at the receiver for producinc duration modulated pulses under control of the received time modulated pulses, said duration modulated pulses having an exponential variation of amplitude with time whose exponent is equal to the exponent of the distorted trapezoidal waveform at the transmitter.
  • a multi-channel electrical communication system as claimed in claim 5 further comprising means for eliminating effects due to distortion of the trapezoidal waveform having an exponential variation of voltage of current with time, said means at the receiver for producing duration modulated pulses including a capacity-resistance network having the same time constant as the trapezoidal waveform generator network at the transmitter and means for applying the potential across a series connected resistance-cavoltage with aesasos l7 pacity of said network as a controlling potential to trigger a pulse generator.
  • a multi-channel electrical communication system as claimed in claim further comprising means for eliminating eifects due to distortion or the trapezoidal waveform having an exponential variation of voltage or current with time, said means at the receiver for producing duration modulated pulses including a capacity-resistance network having the same time constant as the trapezoidal waveform generator network at the transmitter, means for applying the potential across a series connected resistance-capacity of said network as a controlling potential to trigger a pulse generator, a demodulator comprising a multivibrator type of circuit having one stable condition and having said series resistance-capacity of said network in the cathode grid circuit of one valve, means for feeding said network with pulses from a distributor system to trigger the circuit into its unstable condition, means for applying the received train of transmitted distorted pulses to trigger the circuit hack into its stable condition, and means for deriving from the duration modulated pulses obtained at any electrode of the multivibrator, the intelligence wave.
  • a multi-channel electrical communication system as claimed in claim 5 further comprising means for eliminating eflects due vto distortion of the trapezoidal waveform having an exponential variation of voltage or current with time, said means at the receiver for producing duration modulated pulses including a capacity-resistance network having the same time constant as the trapezoidal waveform generator network 'at the transmitter, means for applying the potential across a series connected resistance-capacity of said network as a controlling potential to trigger a pulse generator, a first gas discharge valve having in its cathode circuit a series connected resistance-capacity combination having a time constant equal to the time constant of the trapezoidal waveform generator at the transmitter,
  • the demodulator comprises means for producing under the control pulses at the receiver includes a resistance-capacity network.
  • said modulator includes a resistance-capacity network means for feeding said network with pulses of rectangular waveform to produce across said capacity a trapezoidal waveform, and means for applying said trapezoid-a1 waveform together with the intelligence wave to control a pulse generator for the production of time modulated pulses.
  • a system as claimed in claim 14 having a demodulator comprising a multivl-brator circuit arrangement having said capacity-resistance network connected in the cathode grid circuit oi one valve, means for feeding said network with pulses of rectangular waveform at the operating frequency to trigger the multivibrator over, means for applying the received train of transmitted pulses to trigger the circuit back to its original condition and means for deriving from the duration modulated pulses in the output of said multivibrator, the intelligence wav 18.
  • a system as claimed in claim 14 having a demodulator comprising a first gas discharge valve having a series connected resistance capacity combination in its cathode circuit, means for applying to the control grid of said first valve a series of pulses having the operating repetition frequency of the received time modulated pulses,
  • a second gas discharge valve connected across said resistance and means for applying to a control electrode of said second valve the received train of time modulated pulses to i nite said second valve when the first valve is passing current, theigni-tion of said second valve placing a short circuit across said resistance valves to extinguish and means for terminals of said resistance, the intelligence wave.

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  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Selective Calling Equipment (AREA)
  • Arrangements For Transmission Of Measured Signals (AREA)
  • Radar Systems Or Details Thereof (AREA)
  • Time-Division Multiplex Systems (AREA)
US602804A 1944-05-26 1945-07-02 Multichannel time modulated electrical pulse communication system Expired - Lifetime US2489302A (en)

Applications Claiming Priority (1)

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GB10308/44A GB587941A (en) 1944-05-26 1944-05-26 Improvements relating to multi-channel electrical pulse communication systems

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US2489302A true US2489302A (en) 1949-11-29

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US (1) US2489302A (xx)
BE (1) BE472159A (xx)
ES (1) ES177701A1 (xx)
FR (1) FR58659E (xx)
GB (1) GB587941A (xx)
NL (1) NL72326C (xx)

Cited By (13)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2536654A (en) * 1947-01-04 1951-01-02 Rca Corp Pulse multiplex transmission system
US2556179A (en) * 1946-03-02 1951-06-12 Int Standard Electric Corp Multiple pulse producing system
US2604592A (en) * 1947-10-21 1952-07-22 Standard Telephones Cables Ltd Pulse demodulator system
US2739239A (en) * 1953-03-05 1956-03-20 Inst Textile Tech Imperfection counter
US2740839A (en) * 1946-04-16 1956-04-03 Int Standard Electric Corp Multiplex electric communication system
US2744959A (en) * 1950-05-17 1956-05-08 Hartford Nat Bank & Trust Co Pulse-code modulation transmitter
US2760003A (en) * 1950-05-17 1956-08-21 Hartford Nat Bank & Trust Co Pulse-code modulation transmitter
US2773641A (en) * 1951-01-26 1956-12-11 Goodyear Aircraft Corp Electronic multiplier
US2808204A (en) * 1956-05-08 1957-10-01 Gen Electric Binary digital computing apparatus
US2894127A (en) * 1954-10-26 1959-07-07 Collins Radio Co Pulse decoding means
US2904682A (en) * 1955-08-22 1959-09-15 Lockheed Aircraft Corp Frequency ratio detector
US2977576A (en) * 1956-12-13 1961-03-28 Bell Telephone Labor Inc Transistor timing circuit
US3568077A (en) * 1968-09-03 1971-03-02 Northrop Corp Pseudo voltage controlled oscillator

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2559661A (en) * 1947-04-02 1951-07-10 Int Standard Electric Corp Multichannel electrical pulse communication system
NL74227C (xx) * 1948-09-11

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2227596A (en) * 1938-03-31 1941-01-07 Rca Corp Signaling system
US2262838A (en) * 1937-11-19 1941-11-18 Int Standard Electric Corp Electric signaling system
US2391776A (en) * 1943-05-29 1945-12-25 Rca Corp Intelligence transmission system
US2403210A (en) * 1942-12-04 1946-07-02 Butement William Alan Stewart Multiplex pulse modulation system
US2408077A (en) * 1944-08-25 1946-09-24 Standard Telephones Cables Ltd Multichannel system
US2413023A (en) * 1944-01-06 1946-12-24 Standard Telephones Cables Ltd Demodulator

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2262838A (en) * 1937-11-19 1941-11-18 Int Standard Electric Corp Electric signaling system
US2227596A (en) * 1938-03-31 1941-01-07 Rca Corp Signaling system
US2403210A (en) * 1942-12-04 1946-07-02 Butement William Alan Stewart Multiplex pulse modulation system
US2391776A (en) * 1943-05-29 1945-12-25 Rca Corp Intelligence transmission system
US2413023A (en) * 1944-01-06 1946-12-24 Standard Telephones Cables Ltd Demodulator
US2408077A (en) * 1944-08-25 1946-09-24 Standard Telephones Cables Ltd Multichannel system

Cited By (13)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2556179A (en) * 1946-03-02 1951-06-12 Int Standard Electric Corp Multiple pulse producing system
US2740839A (en) * 1946-04-16 1956-04-03 Int Standard Electric Corp Multiplex electric communication system
US2536654A (en) * 1947-01-04 1951-01-02 Rca Corp Pulse multiplex transmission system
US2604592A (en) * 1947-10-21 1952-07-22 Standard Telephones Cables Ltd Pulse demodulator system
US2744959A (en) * 1950-05-17 1956-05-08 Hartford Nat Bank & Trust Co Pulse-code modulation transmitter
US2760003A (en) * 1950-05-17 1956-08-21 Hartford Nat Bank & Trust Co Pulse-code modulation transmitter
US2773641A (en) * 1951-01-26 1956-12-11 Goodyear Aircraft Corp Electronic multiplier
US2739239A (en) * 1953-03-05 1956-03-20 Inst Textile Tech Imperfection counter
US2894127A (en) * 1954-10-26 1959-07-07 Collins Radio Co Pulse decoding means
US2904682A (en) * 1955-08-22 1959-09-15 Lockheed Aircraft Corp Frequency ratio detector
US2808204A (en) * 1956-05-08 1957-10-01 Gen Electric Binary digital computing apparatus
US2977576A (en) * 1956-12-13 1961-03-28 Bell Telephone Labor Inc Transistor timing circuit
US3568077A (en) * 1968-09-03 1971-03-02 Northrop Corp Pseudo voltage controlled oscillator

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ES177701A1 (es) 1947-06-01
FR58659E (fr) 1954-03-02
GB587941A (en) 1947-05-09
BE472159A (xx)
NL72326C (xx)

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