US2277192A - Multiplex signal-translating system - Google Patents

Description

March 24, 1942. J. C. wlLsoN 2,277,192

.MULTIPLEX SIGNAL-TRANSLATING SYSTEM Filed May' 2e, 1940l 2 sheets-sheet 1 March 24,'1942. J. c. wlLsoN I MULTIPLEX SIGNAL-TRANSLATING SYSTEM Filed May 2s, 1940 2 sheets-sheet 2 vdi l UEE.

.All QSE' SlIOA s'uoA suOA SlloA INVENTOR J HN G. WILSON NE Y ATTO R N EY Patented Mar. 24, 1942` MULTIPLEX SIGNAL-TRANSLATING SYSTEM John C. Wilson, Bayside, N. Y., assignor to Hazel-Y tne Corporation, a corporation of Delaware K l Application May 28, 1940, Serial No. 337,569

v(Cl. 179-15) 13 Claims.

This invention relates to a multiplex signal'- translating system in which a plurality of signalinput channels are successively operatively coupled through a signal-transmission channel to a plurality of signal-output channels in such a way that the signal-transmission Vchannel is used at any given instant only for connecting one of the signal-input channels to its corresponding signal-output channel.

Such a multiplex signal-translating system is V commonly referred to as a shared-time multiplex system, to distinguish it from the more widely-used shared-frequency system in which the frequency range of the signal-transmission vchannel is divided into sub-ranges by lters, each sub-range being continuously available for con-l nection between a pair of signal-input and signaloutput channels. I

The above-mentioned type of multiplex signaltranslating system has been embodied in a number of types of prior art apparatus. For instance, the transmission channel has comprised a channel having a wide transmission pass band-and the system has beenused to couple several corresponding input and output channels which translate signals of a frequency range which is narrow with respect to the pass band of the transmission channel. Such an arrangement has been used in telephone and -telegraph systems so that a single transmission line or channel can be utilized to transmit a plurality of different telephonic or telcgraphic signals.

synchronously-operating cathode-ray tube switching arrangements have been utilized in the input and output channels of certain of the prior 4 art systems of the type describedin order successively and cyclically to couple only each of the signal-input channels at any instant with its corresponding signal-output channel through the transmission channel. Such switching arrangements must be operated at a very high frequency, that is, a frequency which is higher than the frequency of the highest-frequency signal component to be transmitted, so that several portifns of each cycle of such highest-frequency signal component to be transmitted are represented in the transmission channel. If this conditicn is met and a suiiicient number of these portions are transmitted for each cycle of the highest-frequency signal component to be transmitted, the fidelity of reception is not unduly impaired and the arrangement has the advantage of allowing the simultaneous transmission of a plurality of different signals over' a single transmission channel.

However, in prior art systems of the type mentioned, it has been the practice to allot a given fraction of the cycle of operation of the synchronous switching means to each signal which the transmission channel and its associated synchronous switching arrangement is capable of transmitting so that the number of separate signals which may be transmitted over such an arrangement is limited by the fidelity oftransmission required. The fidelity is determined by the number of times a given input channel, and its corresponding output channel are connected together through thetransmission channel during the transmission of a cycle of the highest-frequency component of the signal being translated. For instance, the limiting number of separate signals which may be transmitted over a givenV transmission channel may be 100. This means that, in a telephone system, for instance, one transmission channel must be provided for each 100 subscribers. However, all channels of such an arrangement are very infrequently, or never, used simultaneously; in fact, it is usually found in practice that, out of a given number of signalinput channels, the probability is that only a small percentage thereof` will lbe used simultaneously. This means that if .a given transmission line or channel is capable of transmitting 100 separate signals simultaneously, it would serve for several hundred subscribers or signalinput channels providing only those being used were actually connected to the synchronous ltransmitting arrangement at a given instant.

However, this operation is not, in general, practical due to the large number of switches and the complexity of the switching operations required. It is, therefore, particularly desirable to provide an arrangement of the general type described in which a large number of input and output channels may be coupled to the syndivided equally only between such channels in use.

It is an object of the invention, therefore, to provide an improved multiplex signal-translating system of the general type under discussion.

It is another object of the invention to provide a multiplex signal-translating system by which a plurality of signal-input channels and corresponding signal-output channels, only a few of which are in operation during a given interval,

may be successively and cyclically coupled on channel, a plurality of signal-input channels. and a plurality of corresponding signal-output channels. The system includes means for cyclically simultaneously connecting and simultaneously disconnecting the signal-input channels and corresponding signal-output channels to the signal-transmission channel in a predetermined sequence and at a frequency which is I higher: than that of the highest-frequency signal component to be transmitted from any of the signal-input channels over the Signal-transmission channel. Means are further provided for controlling the fraction of an operating cycle of the rst-named means that any particular signal-input channel which is in use and its corresponding signal-output channel are connected together through the signal-transmission channel inversely in accordance with the number of signal-input channels which are in use during the operating cycle..

As used in this speciilcation, 'the term frequency which is higher than that of the highest-frequency signal component to be transmitted has reference to the frequency of the highest modulation frequency in case a modulated-carrier signal' transmitted and in any case has reference to the highest-frequency signal which is transmitted and reproduced. `4

synchronously-operating cathode-ray 'tube switching arrangements have been utilized in the input and output channels of certain of the prior art systems of the shared-time type in order successively and cyclicalLv to couple only each of the signal-input channels at any instant with its corresponding signal-output channel through the transmission channel. The present invention is concerned with systems in which such switching arrangements are operated at a very high rate,-

' sive, and a common ground return; and a plurality of corresponding signal-output channels, represented by the single conductors |946, in-

clusive. and a common ground return. Means are provided for successively and cyclically simultaneously connecting and simultaneously disconnecting the signal-input channels II-I8, inclusive, and corresponding signal-output channels Il-2i, inclusive, to the signal-transmission channel Il, I8 at a predetermined frequency which is higher than that of the highest-frequency signal component to be transmitted from any of the signal-input channels II-I8, inclusive, over the signal-transmission channel III, I0 to corresponding signal-output channels I9-28, inclusive. This means comprises a cathode-ray tube 21, utilized t as a multiple-circuit switching device at the signal-input end of the transmissionl channel I8, I0, and a similarly-connected cathode-ray tube 28, utilized as a multiple-circuit switching device at the output end of the transmission channel Ill, I0. Each of the cathode-ray tubes 21 and 28 comprises, in the order named, a conventional electron gun which may consist of a cathode and an accelerating anode 3 I ,vertical deecting plates 32, 33, horizontal deflecting plates 34, 85, a collector electrode 36, and a plurality of rectangular target electrodes, of which two are identifled as 31, 38, the letters a and b being associated with the reference numerals identifying elements of tubes 21 and 28, respectively. Means, to be hereinafter described in detail, are provided for deilecting the beams of tubes 21, 28 to scan their respective that is, a rate which is higher than the frequency of the highest-frequency signal component to be reproduced, so that on the average, at least some portion of each cycle of such highest-frequency signal component to be reproduced is represented in the transmission channel. If this condition is metthe fidelity of reception is not unduly impaired and the arrangement has the advantage of allowing-the simultaneous transmission of a plurality of different signals over a single transmission channel.

For a better understanding of the present invention, together with other and further objects thereof, reference is had to the following descrip; tion taken in connection with the accompanying drawings, and its scope will be pointed out in the appended claims. v

Fig. 1 of .the drawings is a circuit diagram, partly schematic, of a complete multiplex signaltranslating system embodying the invention, while Figs. 2li-5, inclusive, comprise graphs used to explain certain of the operating conditions of the system of Fig. l.

Referring now more particularly to Fig. 1 of the drawings, there is shown therein a multiplex signal-translating system comprising a signal-transmission channel which may be either a radio or wire channel and is represented by lines I3, I0; a plurality of signal-input channels, represented,

target electrodes, including electrodes 31 and 38, synchronously in the two cathode-ray tubes at a frequency which is higher than that of the highest-frequency signal component to be transmitted from any of the signal-input channels over the signal-transmission channel.

Input channels I4 and I1 only are illustrated as being connected, respectively, to target electrodesv 31s and 38; of cathode-ray tube 21, although it will be understood that any practicable number of target electrodes can be utilized in cathode-ray tube 21, each of which is operatively connected to an input channel of the type represented by conductors II-I8, inclusive, only the two target electrodes being shown operatively connected for the purposes of illustration herein. The signal-input channel I4 is connected to target electrode 31s through an amplifier 40 while signal-input channel I1 is similarly coupled to target electrode A38 through an amplifier 4I,'this latter channel being shown in dotted lines for the sake of clarity. l A

The cathode-ray tube switching device 28 comprises also a control grid 42s and output signals, derived from collectorelectrode 36a of cathoderay tube 21, are translated through an amplifier 44, the signal-transmission channel III, III, and an amplier 45 to the control grid of cathoderay tube 28. A signal-translating device 46, corresponding to signal-input channel I4, is coupled to target electrode 31h of cathode-ray tube 28, while a signal-translating device 41, corresponding to signal-input channel I1, is correspondingly coupled'to target electrode 38s of cathode-ray tube 28. Switches S, 1, 8, and 9 are provided vso that any signal-input channel and its correaa'zrgica therein. the system sotar described is' conventional and its operation will bewellunderstood by those skilled in the art. .Speciiical1y. each input circuit is connected during predetermined intervals as the successive targets o! tubes 21 and 28 are scanned through transmission line In, I with its corresponding output circuit.

Each portion of a signal which is translated by the transmission channelpl, i0 is effective to vary theelectron stream oi tube 28 in accordance with the translated signals and, therefore. tovary the output derived from the target electrodes ot the tube in accordance with the translated signals. It the frequency of the operating cycle of the synchronous connecting and disconnecting means is very high and the pass band of the channel I0, I0 is adequate, the ildelityoi transmission oi' any given signal is-not unduly materially impaired.

Coming now to the portion of the system of lFig. 1 involving the present invention, there is provided means for controlling the fraction of an operating cycle of the synchronous switching has risen suiliciently to cause tube 64 to become conductive. This cycle is repeated to provide saw-tooth scanning voltages for scanning tube 21 in the horizontal direction.

In rorder o scan cathode-ray'tube 21 inthe vertical dir tion, there is provided a ratchet" scanning-potential generator comprising a con denser 66 and a resistor 61 to form a differentiating circuit such that the high rate of change of voltage, corresponding vto the rapid discharge o( condenser 66 through tube 64 causes a pulse voltage to appear across the resistor 61. This pulse voltage across resistor 61 is applied to the input circuit of a vacuum tube 66 which has its anode-cathode circuit4 included in the charging circuit o! a condenser 58. A suitable bias is provided for tube 69 by means of source 68 which, in the absence of such a voltage pulse. biases the tube 69 to cutoff. The discharge circuit'of condenser 68 includes a gas-filled tube 1B having its anode-cathode electrodes coupled across con- -denser 58 and having a control electrode 'so means that any particular sgnal-input channel which is'in use and its corresponding signal-output channel are connected together through the signal-transmission channel I0, I0 inversely in accordance with the number of signal-input channels which are in use at the time. That is, an arrangement is provided whereby only those signal-input channels and their corresponding signal-output channels which are being utilized to translate a conversation or other'signal are caused to share the effective portion of theoperating cycle.

The system comprises means for scanning the target electrodes of each of cathode-ray tubes 21 and 28 at avery high frequency in the absence of any signal input to the transmission line I0, I0 and for causing the scanning of such target electrodes to which signals are applied to be very materially retarded in order that substantially the total time of a scanning cycle of the synchronous switching means he devoted only to those target electrodes which are connected to signal-input channels in use. In order to provide this type of scanning, there is provided a saw-tooth scanning oscillator, including con-,-

denser 56 adapted to be charged and discharged. to provide scanning potentials in the horizontal y direction. In order to charge condenser 56 at a relatively slow rate to provide horizontal de` ection for the cathode-ray scanning beam voi tube 21, there is providedv a vacuum tube 62 through the anode-cathode circuit of which condenser 56 is coupled to the high-voltage source 60. A suitable screen-voltage operating potential ior Vacuum tube 62 is provided by moans of voltage-dividing resistor 63 coupled across the high-voltage source 63. In order to discharge condenser 58 after the voltage thereof has risen to a predetermined value, there is provided a tube 64. which may be a gas-filled tube or a tube suitably coupled to provide regeneration, -having its anode-cathode electrodes coupled across condenser. 56 and having a control grid to which is applied a suitable negative bias from source 65. The arrangement is such that. for a given conductance of vacuum tube 62, the condenser 56 is relatively slowly charged to a predetermined voltage, as represented bydotted line 14 of Fig. 2d, through vacuum tube 62, as indicated by charging line 13 of Fig. 2a, and is rapidly discharged through tube 66. as indicated by line 15 of Fig. 2a, after the potential .of condenser 56 circuit of vacuum tube so that tube 69 is caused to be conductive for a predetermined interval to charge condenser 5B a predetermined increment or step, for instance, the step 16 of Fig. 2b, which represents the voltage-time characteristic of the condenser 58 of the ratchet horlzontal scanning `oscillator. The increment of charging voltage 'of condenser 58 during each of these charging intervals is just suicient to step the scanning beams of cathode-ray tube 21 from one horizontal row of target electrodes to the next succeeding lower row of target electrodes.

In order to `provide a suitable deflection, in the absence of potentials on condensers 5 6 and 58, so that the beam of cathode-ray tube 21 is on the first target of the first row of targets. there is provided an initial deflection bias for the horizontal scanning electrodes 34a. 35a by means of resistor 59 coupled across the highvoltage source 60 and having a tap thereoncou- Y pled tofscanning plate 35a of tube 21, while a similar bias resistor 6I is provided for plate 32a of tube 21.` The circuit is thus proportioned so in the Journal of the Institution of Electrical- Engineers (London) in an article of L. H. Bedford and O. S. Puckle entitled A velocity-modulation television system." vol. 75. No. 451, pp. 63-82.

-It will' be understood that cathode-ray tube 28 at the receiving station is similarly scanned and, for this purpose,v the scanning potential applied to scanning plates 36a', 35a of tube 21 is transmitted over a channel or line 34 and applied to the input circuit of a controlled scanner 1 I. It will be understood that suitable initial biasing potentials are provided for the scanning plates 32e and 35e of cathode-ray tube 28 in a manner similar to'that described for cathoderay tube 21. the portion oi the system of Fig. 1 included within the dotted line 12 is duplicated in the lcontrolled scanner 1l in order to provide suit- It will also be understood that] able scanning potentials for application to plates 32s, 33s of cathode-ray tube 28.

Reference is made to the graphs of Figs. 2a and 2b for an explanation of the scanning or operating cycle of cathode-ray tubes 21 and 28 under the conditions when none of the signalinput channels is in use. Starting at time to, it is seen that condenser 56 is slowly charged through the vacuum tube 62, as represented by the charging line 13, until its potential rises to that at which tube 64 becomes conductive, as represented by the dotted line 14 of Fig. 2a. At this point. in the cycle, condenser 56 is rapidly discharged as represented by the discharge line 15 and this cycle isrepeated indefinitely. During the time of discharge of condenser 56, as represented by the discharge line 15, a pulse voltage is applied to the input circuit of tube 69 through the differentiating circuit 66, 61, thereby to cause tube 69 to become conductive and partially to charge condenser 58 as represented by the voltage step 16 of Fig. 2b. These steps are repeated during each discharge period of condenser 56 until the discharge potential of condenser 58, represented by the dotted line 11, is reached after which condenser 58 is discharged through tube 10, which is so'biased' that it becomes conductive when its anode-cathode potential reaches that represented by dotted line 11. The circuit is sc proportioned that the discharge potential, represented by dotted line 11, is obtained during the discharge period of condenser 56 following the scanning of the last line of the target electrodes of cathode-ray tube 21.

In order to cause the scanning beam of cathode-ray tubes 21 and 28 to be delayed for a large fraction of a cycle of the synchronous operation thereof only on those of the target electrodes of the tube corresponding to signal-input channels which are in use, there is provided an additional cathode-ray tube 58 for the purpose of providing a control-signal output which varies in accordance with the pattern represented by the particular target electrodes of the cathoderay tube 21 which are being energized through one of signal-input channels lI-I, inclusive. The cathode-ray tube 50 is generally similar to cathode-ray tube 21 and similar circuit elements have identical reference numerals with the added letter c. The scanning plates of cathode-ray tube 50 are connected in parallel with those of tube 21. In order to energize target 31e of cathode-ray tube 50 simultaneously with the transmission of a signal through target 31a of cathode-ray tube 21, there is provided a rectifier 5|, coupled to the output circuit of amplifier 48 and, in turn, having its output circuit coupled through a limiter 52 to target electrode 31e of cathode-ray tube 50. Similarly, there is provided for target electrode 38e of cathode-ray tube 50, a rectifier 54 having an input circuit coupled to the output circuit of amplifier 4I andhaving its output circuit coupled through a limiter 55 to target electrode 38e of cathode-ray tube 50.

There is provided an arrangement for deriving an output from cathode-ray tube 50 to reduce the conductance of vacuum tube 62 during the interval when there is being scanned a target energized from a signal-input channel in use, thereby to retard the charging of condenser 56 instantaneously to retard the rate of scanning of such target in both tubes 21 and 28. For this purpose, there is provided an amplifier 18 which is designed to be quickly responsive and having its inputcircuit coupled to a load resistor 86 in the circuit of the collector electrode 36e of tube 50 and having its output circuit coupled to a. control electrode of vacuum tube 62. Tube 58 is. therefore, scanned synchronously with the scanning of tube 21 and the rate at which electrons are collected at electrode 86 ot tube 50 at any instant depends upon the potential of the target electrode being scanned. For ach energized target o! cathode-ray tube 50 which is scanned, a negative potential pulse is, therefore, developed across the load resistor 36' of collector electrode 36er of tube 50 and applied to amplifier 18 and the amplier is so proportioned that there is also derived therefrom a negative potential pulse effective to reduce the conductance of vacuum tube 62 for the duration of the pulse, thereby to retard the charging of condenser 56.

In order to explain the effect of control tube 50 and its associated apparatus on the circuit of Fig. 1, reference is made to Figs. 3a and 3b. It 1s here assumed that only target electrode 31 or the second target electrode of the first row of targets of each of cathode-ray tubes 21, 28, and 50 is energized, which means that only the signal-input and output channels which are connected through transmission line I0, I8 and through these targets are energized by an input signal for translation. Under these conditions, the scanning potentials derived from the horizontal scanning oscillator including condenser 56 and from the vertical scanning oscillator including condenser 58 are represented by the curves of Figs. 3a and 3b, respectively. It is thus seen that at th'e time to, which corresponds to the beginning of a scanning cycle, the first target of the first row is scanned very rapidly and at the same rate as obtained under the condition of operation illustrated by the curve of Fig. 2a. Therefore, during the time of scanning of the rst target of the rst row, the.voltage across condenser 56 rises in a relatively short time, as represented by charging line 19, approximately to one-third the maximum scanning amplitude rep-- resented by dotted line 14, which is the voltage required to cause tube 64 to become conductive and discharge condenser 56. Thereafter, the second target of the rst row, or target 31e, which is the one assumedto be in use, is scanned and, during this interval, a signal output is derived from collector electrode 36e of tube 50 which is applied to tube 62 through amplifier 18 materially to lowei` its conductance, thereby to reduce the charging rate of condenser 56, as illustrated by the charging line 86. This condition obtains until the voltage across condenser 56 has reached approximately two-thirds the maximum scanning voltage represented by line 14; when the scanning of the target connected to the input channel in use is completed, the control bias derived from the collector electrode of tube 50'falls and the charging'rate is again increased to its maximum value as represented by the charging line 8l. The remainder of the scanning cycle is substantially identical to that described with reference to Fig. 2a. The corresponding ratchet voltage of condenser 58 is lillustrated in Fig. 3b. In the arrangement described above, it is assumed that modulated-carrier signals are to be translated from the input channels to the output channels, for the reason that, under this condition oi' operation, a potential always exists on the target electrode of cathode-ray tube 50 corresponding to a particular input channel whenever that input channel is being utilized to translate a signal,

irrespective of Whether a modulation signal is being transmitted atthe .particular instant.V vIt will be understood, however, that applicants invention is not limited to arrangements in which l modulated-carrier signals are translated.

It is seen, therefore, that applicants system is eiective to cause the greatest part of the operating cycle of the synchronous switching meansto be devoted to the scanning of the second target of the rst row. which is the only target connected to a signal-input channel in use.

In Figs. 4a andfib there are shown, respectively, curves which correspond to those of Figs. 3a and 3b under the conditions that the signalinput channels are in use which Aare connected to the second target of the rst row, the i-lrst target of the third row, and the last target of the fourth row. Under these conditions, it is seen thatthe charging line 82 represents the'charging of con-V denser 56 during the time that the flrst target of the first row is rapidly scanned, the charging line' 83 corresponds to the relatively slow scanning of the second target of the rst row, and the line 84 corresponds to the rapid scanning of the third target of the first row. After this target has been scanned, the discharge voltage 'I4 of condenser 56 is reached and the tube 64 becomes conductive to discharge condenser 56 as illustrated by the discharge line 85. The charging line of condenser 56du'ring the scanning of the targets of the second row, none of which is assumed to be energized, is illustrated by the charging line 86 which is followed by the discharge of condenser 56 as represented by the line 8l. The relatively slow charging. of condenser 56 during the scanning of the rst target rapid charging of condenser 56 during the scanning of the rst and second targets of the fourth row is represented by the charging line 9|, and the relatively slow charging during the scanning of `the last target of the last row is represented by the line 92, after which the cycle repeats, beginning at time t1.

It is thus seen that applicants system comprises means for controlling the fraction of an operating cycle that any particular signal-input channel which is in use and its corresponding signal-output channel are connected together through the transmission channel inversely in accordance' with the number of signal-input channels which are in use and that means are provided to cause only the particular signal-input channels and their corresponding signal-output channels which are in use during an operating cycle to share the eiective portion of the operating cycle. As so far described, this is accomplished by extending the time of each operating cycle in accordance with the number of signalinput channels which are in use. Furthermore, it is seen that the sum of all the operating-cycle fractions corresponding to input circuits which are in use is a substantial part of the operating cycle and preferably the arrangement-is so designed that the sum of all said fractions is substantially the whole of the operating cycle.

From the operating characteristics of Figs, 3a, 3b and 4a, 4b, it is seen that the period of a scanning cycle in the system, as so far described,V

varies in accordance with the number of input channels which are energized during the operating cycle and that the time of each operating ,cycle is extended in accordance with the number of signal-input channels which are in use.

'This variation in the period of the scanning cycle maybe undesirable under certain conditions of Voperation and, for the purpose of maintaining the period of each operating cycle substantially constant while effecting an operation generally in accordance with that described above, there r: ay be provided in addition an arrangement for controlling the gain of ampliiier 18 inversely in accordance with the number of signal-input channels which are in use. For this purpose, there is provided a gain-control means 93 having an input circuit coupled to collector electrode 36 ofcathode-ray tube 50 and having an output circuit from which is derived a'potential utilized to control the gain of amplifier 18. The gainccntrolmeans 93 comprises a vacuum-tube amplii'ler 94 having an input circuit coupled to co1- lector electrode 36C of tube 50 and an output circuit coupled to the input electrodes of a vacuum tube 95 included in a counter circuit. The output circuit of tube 95 comprises a load resistor 96 and a source 91 of unidirectional operating voltage coupled in series. -There is also coupled across the series combination a series-connected diode 98 and condenser |00. A resistor 99 -is connected between a terminal common to diode 98 and condenser |00 and a tap on source 91. The voltage across condenser |00 is utilized to control the gain of amplier 18, being applied thereto through a suitable lter.

VIn considering the operation of the circuit of gain-control means 93, it will be assumed that vacuum tube 95 is so biased as to become conductive only when a target electrode of cathoderay tube is being scanned which has a signal applied thereto. It will thus be seen that condenser |00 is charged slightly positively from the source 97 during the time When tube 95 is nonconductive through the charging circuit including resistor 99. Each time tube 95 becomes conducting, condenser |00 is partially discharged through diode 98. The degree to which condenser |00 is discharged, therefore, depends upon the number of targets which are in use. There- Y fore, under each condition of operation of the signal-input channels in use.

transmitting arrangement described, the potential which exists across condenser |00 varies in accordance with the number of target electrodes of cathode-ray tube 50 which are connected to This potential is applied to one or more of thecontrol grids -of vacuum tubes in amplier T8 to decrease their amplification in accordance with the magnitude of the control voltage in a manner Well under-- stood in the art.

in order to explain the operation of the system as a Whole, taking into account the operation of the gain-control arrangement 93, reference is made to the curve of Fig, 5 which is somewhat similar to the curve of Fig. 4a, the general shape of the curve being the same and the onlyrditference being that the over-all period of the scanning cycle tc--r is -materially reduced by the operation of the gain-control means 93, and is maintained within relatively narrow limits for a Wide range of variation in the number of signal-input channels in use'. Thus, considering again the conditions of operation assumed in describing the system with reference to Figs. 3a and 4a, it is seen that the period of an operating," cycle is materially increased, with respect to that when onlyone of the signal-input channelsis in use, when three target electrodes are energized, as illustrated by the curve of Fig. 4a; that is, the period of the scanning cycle representedby the curve of Fig. 4a is materially longer than that represented by the curve of Fig. 3a. Under the operation of the gain-control arrangement 93, however, it is seen that the period of a. complete scanning cycle when three target electrodes are energized is materially decreased, as illustratedl by the curve of Fig. 5. Therefore, the effect of the gain-control arrangement is to cause the period of an operating cycle, when the signalinput -channels connected to a plurality of control electrodes are in use, to approach, or to become substantially equal to,the period of a scanning cycle when only one` signal-input channel is in use.

While, in the arrangement described, the scahning beams of tubes 21, 28, and 50 are caused to scan more slowly the target electrodes corresponding to signal-input and signal-output channels actually in use, that is, which are energized, by means of potentials derived from the channels in use, it will be understood that the in vention is not limited to such an arrangement but that the speed of scanning of the several target electrodes can be controlled in response to any suitable operating condition of the system.

While there has been described what is at prising, a signal-transmission channel, a plurality of signal-input channels, a. plurality of corresponding signal-output channels, means for cyclically simultaneously connecting and simultaneously disconnecting said signal-input channels and corresponding signal-output channels to said signal-transmission channel ina predetermined sequence and at a frequency which is higher than that of the highest-frequency signal component to be transmitted from any of said signal-input channels over said signal-transmission channel, and means for controlling the fraction of an operating cycle of said rst-named means that any-particular signal-input channel which is in use and its corresponding signal-output channel are connected together through said signal-transmission channel inversely in accordance with the number of signal-input channels which are in use during said operating cycle.

2. A modulated-carrier signal-translating system comprising, a modulated-carrier signaltransmission channel, a plurality of modulatedcarrier signal-input channels, a plurality of corresponding modulated-carrier signal-output channels, means for cyclically simultaneously connecting and simultaneously disconnecting said signal-input channels and corresponding signaloutput channels to said signal-transmission channel in a predetermined sequence and at a frequency which is higher than that of the highest modulation-frequency signal component to be transmitted from any of said signal-input channels over said signal-transmission channel, and means for controlling the fraction of an operating cycle of said rst-named means that any particular signal-input channel which is in use and its corresponding signal-output channel are connected together through said signaltransmission. channel inversely in accordance with the number of signal-input channels which are in use during said operating cycle.

3. A multiplex signal-translating system comprising, a signal-transmission channel, a plurality of signal-input channels, a plurality of corresponding signal-output channels, means for cyclically simultaneously connecting and simultaneously disconnecting said signal-input channels and corresponding signal-output channels to said signal-transmission channel in a predetermined sequence and at a frequency which is higher than that of the highest-frequency signal component to be transmitted from any of said signal-input channels over said signal-transmission-channel, and means for controlling the fraction of an operating cycle of said first-named means that any particular signal-input channel which is in use and its corresponding signaloutput channel are connected together through said signal-transmission channel inversely in accordance' with the number of signal-input channels4 which are` energized during said operating cycle and for maintaining the sum of all said fractions corresponding to signal-input circuits which are in use during said operating cycle a substantial part of the operating cycle.

4. A signal-translating system comprising, a signal-transmission channel, a plurality of signalinput channels, a plurality of corresponding signal-output channels, means for cyclically simultaneously connecting and simultaneously disconnecting said signal-input channels and corresponding signal-output ,channels to said signal-transmission channel in a predetermined sequence and at a frequency which is higher than that of the'highest-frequency signal component to be transmitted from any of said signal-input channels over said signal-transmission channel, and means for controlling the fraction of an operating cycle of said first-named means that any particular signal-input channel which is in use and its corresponding signal-output channel are connected together through said signal-transmission channel inversely in accordance with the number of signal-input channels which are energized during said operating cycle and for maintaining thev sum of all said fractions corresponding to signal-input circuits which are in use during said operating cycle a major portion of the operating cycle.

5.. A multiplex signal-translating system comprising, a signal-transmission channel, `a plurality of signal-input channels, a plurality of corresponding signal-output channels, means including Vsynchronously-scanned cathode-ray tubes for cyclically simultaneously connecting and simultaneously disconnecting said signalinput channels and corresponding signal-output channels to said signal-transmission channel in a predetermined sequence and at a frequency which is higher than that of the highest-frequency signal component to be transmitted from any of said signal-input channels over said signal-transmission channel, and means `for controlling the fraction of an operating cycle of said first-named means that any particular signalinput channel which is in use and its corresponding signal-output channel are connected together through said signal-transmission channel inversely in accordance with the number of signal-input channels which are in use during said operating cycle.

6. A multiplex signal-translating system comprising, a signal-transmission channel, a plurality of signal-input channels, a plurality.of corresponding signal-output channels, a cathoderay tube adapted to be connected with said signal-input channels, a cathode-ray tube adapted to be connected with said signal-output channels, means including said cathode-ray tubes and means for synchronously scanning said tubes for cyclically simultaneously connecting and simultaneously disconnecting said signal-input channels and corresponding signal-output channels to said signal-transmission channel in a predetermined sequence and at a frequency which is higher than that of the highest-frequency signal component to be transmitted from any of said signal-input channels over said signal-'transmission channel,`and means for controlling said scanning means to control the fraction of an operating cycle of said first-named means that any particular signal-input channel which is in use and its corresponding signal-output channel are connected together through said signal-transmission channel inversely in accordance with the number of signal-input channels which are energized during said operating cycle.

7. A multiplex signal-translating system comprising, a signal-transmission channel, a plurality of signal-input channels, a plurality of corresponding signal-output channels, a cathoderay tube adapted to be connected with said input channels, a cathode-ray tube adapted to be connected with said output channels, means including said cathode-ray tubes and means for synclironously scanning said tubes for cyclically simultaneously connecting and simultaneously disconnecting said input channels and corresponding signal-output channels to said signal-transmission channel in a predetermined sequence and at a frequency which is higher than that of the highest-frequency signal component to be transmitted from any of said signal-input channels over said signal-transmission channel, and means for instantaneously retarding the rate of scanning, only during the period said tubes are operative to connect a signal-input channel which is in use with said signal-transmission channel, whereby the fraction of an operating cycle of said rst-named means that any particular signal-input channel which is in use and its corresponding signal-output channel are connected together through said signal-transmission channel is controlled inversely in accordance with the number of signal-input channels which are in use=during said .operating cycle.

8. A multiplex signal-translating system comprising, a signal-transmission channel, a plurality of signal-input channels, a plurality of corresponding signal-output channels, means comprising a condenser and means for charging and discharging said condenser for cyclically simultaneously connecting and simultaneously disconnecting said signal-input channels and corresponding signal-output channels to said signaltransmission channel in a predetermined sequence and at a frequency which is higher than that of the highest-frequency signal component to be transmitted from any of said signal-input channels over said signal-transmission channel, and means for controlling the rate of change of charge of said condenser to decrease the rate of scanning only during the period a signalinput channel which is in use is connected to said signal-transmission channeL'whereby the fraction of an operating cycle of said firstnamed means that any particular signal-input channel which is in use and its corresponding signal-output channel are connected together through said signal-transmission channel is controlled inversely in accordance with the number of signal-input channels which are in use during said operating cycle.

9. A multiplex signal-translating system comprising, a signal-transmission channel, a plurality of signal-input channels, a plurality of corresponding signal-output channels, a cathoderaytube adapted to be connected with said signal-input channels, a cathode-ray tube adapted to be connected with said signal-output vchannels, means including said cathode-ray tubes land means for synchronously scanning said tubes, comp-rising a condenser and means for charging and discharging said condenser, for cyclically simultaneously connecting and simultaneously disconnecting said signal-input channels and corresponding signal-output channels to said signal-transmission channel in a predetermined sequence and at a frequency which is higher than that of the highest-frequency signal component to be transmitted from any of said signal-input channels over said signal-transmission channel, and means for controlling the rate of change of charge of said condenser to decrease the rate of scanning only during the period a signal-input channel which is in use is connected to said signal-transmission channel, whereby the fraction of an operating cycle of said first-named means that any particular signal-input channel which is in use and its corresponding signal-output channel are connected together through said signal-transmission channel is controlled inversely in accordance with the number of signal-input channels which are in use during said operating cycle.

10. A multiplex signal-translating system comprising, a signal-transmission channel, a -plurality of signal-input channels, a plurality of corresponding signal-output channels, means for cyclically simultaneously connecting and simultaneously disconnecting said signal-input channels and corresponding signal-output channels to said signal-transmission channel in a predetermined sequence and at a, frequency which is higher than that of the highest-frequency signal component to be transmitted from any of said signal-input channels over said signal-transmission channel, and means responsive to a control derived from channels in use for maintaining the time of each operating cycle of said first-named means substantially constant during periods when any of said channels are in use and for controlling the fraction of an operating cycle of said rstnamed means that anyparticular signal-input channel which is in use and its corresponding signal-output channel are connected together through said signal-transmission ychannel inversely in accordance with the number of signalinput channels which are in use during said operating cycle.

11. A multiplex signal-translating system comprising, a signal-transmission channel, a plurality of signal-input channels, a plurality of corresponding signal-output channels, a cathoderay tube adapted to be connected with said sig- 'nal-input channels, a cathode-ray tube adapted means for synchronously scanning said tubes,l

, to connect a signal-input channel which is in use with said signal-transmission channel, whereby the fraction of an operating cycle of said rst-named means that any particular signal-input channel which is in use and its corresponding` signal-output channel are connected together through said signal-transmission channel is controlled inversely in accordance with the number of signal-input channels which are energized during said operating cycle, and means responsive to the total number of signal-input channels in use for maintaining the average rate of scanning said cathode-ray tubes substantially constant when any of said channels are in use.

12. A multiplex signal-translating system comprising, a signal-transmission channel, a. plurality of signal-input channels, a plurality of corresponding signal-output channels, a cathoderay tube adapted to be connected with said signal-input channels, a cathode-ray tube adapted' to be connected with said signal-output channels, means, including said cathode-ray tubes and means for synchronously scanning said tubes, for cyclically simultaneously connecting and simultaneously disconnecting said signalinput channels and corresponding signal-output channels to said signal-transmission channel in a predetermined sequence and at a frequency which is higher than that of the highest-irequency signal component to be transmitted from any of said signal-input channels over said signal-transmission channel, and means for extending the time of each operating cycle of said rstnamed means in accordance with the number of signal-input channels which arein use and for controlling the fraction of an operating cycle that any particular signal-input channel which is in use and its corresponding signal-output channel are connected together through said signal-transmission channel inversely in accordance with the number of signal-input channels which are in use during said operating cycle.

13. A multiplex signal-translating system comprising, a signal-transmission channel, a plurality of signal-input channels, a plurality of corresponding` signal-output channels, means for cyclically simultaneously connecting and simultaneously disconnecting said signal-input channels and corresponding signal-output channels -to said signal-transmission channel in a pre-1 determined sequence and at a, frequency which is higher than that of the highest-frequency signal component to be transmitted from any of said signal-input channels over said signal-transmission channel, and means for controlling said rst-naied means to cause only the particular signal-input channels and their corresponding signal-output channels which are in use during an operating cycle-of said rst-named means to be connected together simultaneously and to share the effective portionV of said operating cycle.

JOHN C. WILSON.

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