US2408692A - Signaling system - Google Patents

Description

Oct. l, 1946.

H. vsHoRl:

SIGNALING SYSTEM Filed April 29, 1942 ATTORNEY 0d. l, 1.946. H SHQR 2,408,692

SVIGNALYING SYSTEM Filed April 29, 1942 4 Sheets-Sheet 2 ATTORNEY Oct. l, 1946. H. SHORE SIGNALING SYSTEM Filed April 29, 1942 4 Sheets-Sheet 3 lNvENToR HENRY 'E BY 7i I Ai'roRN et l, 1946.

' AMPLITUDE OF ENERGY O o D o o H. SHORE SIGNALING SYSTEM Filed April 29, 1942 Il F'i l'l/ `Ai'roNEY 4 sheets-sheet 4 lNvEN'roR I #ENR HORE Patented Oct. 1, 1946 Henry Shore, Jackson Heights, N. Y., assignor to Radio Corporation of America, a corporation of..

Delaware 'Application April 29, 194g;

14 Claims.

This invention relates to signaling systems, Yand in particular to methods of transmitting information by telephonic communications or by television transmission, 'in which there are incorporated features for enabling secrecy of the transmitted messages to be maintained.

In accordance With my inventionl provide a transmission system suitablel for use in television or telephone communications for maintaining secrecy utilizing Well known circuit elements and at the same time providing means by use of limiters for obviating the diiculties of clear'k reception introduced by fading. In the method and apparatus used, the source of signals occupying a predetermined band width of frequencies is first separated into a plurality of discreet bands 4 of frequencies. All but one of the bands of frequencies are thereafter transformed or displaced in the frequency spectrum s o as to occupy `the same band of frequencies as the unchanged band of frequencies. The resultant energy of each' of the bands of frequencies is then individually converted into constant-frequency dot energy, the

weight of dots beingv substantially proportionalto the instantaneous value of amplitude of the energy within the band or channel. The inception of the marking interval for each dot of each channel is staggered, so that combining the outputs of a plurality of bands or channels, following their conversion into constant-frequency dots, rthere is obtained a signal Whose dot frequency is as many times the original dot frequency of the constant-frequency variable-dura- Ytion converters as there are channels involved.

This signal is used to actuate the radio transmitter, or may be placeddirectly on the 'wire line for transmission.

At the receiver, the received signals are' detected and the detected signals pass .through a distributor commutator Which distributesjthe constant-frequency variable-dot signals to their respective channels. The so-distributed dotsare then converted back to a signal having variable amplitude, the instantaneous vamplitude being 4proportional to the Weight of the dot. The variable amplitude signals corresponding to the channels in which the frequency range was transformed are re-transformed back to occupy the same band of frequencies that they Yoriginally occupied at the transmitter. The signal energy from the three channels is thereafter combined to reproduce the original signal covering the orig'- inal predetermined band of frequencies.

In order to prevent overlapping of the dots and to insure interchannel stability of freserial ivo. 440,893

quencyga single generator of sawtooth energy is provided. This'is" the source which is supplied to the constant'v-frequency variable-dot converter and, in one case, the energy is`fed directly to the channel in which 'the frequency is not transformed; Energyfron the sawtooth joscillator is also fed-to eachof the `other converters with an appropriate phase shift' introduced in each of the supply lines.V The phase shiftis equal to where N is the number of bands into which the original band of frequency vis broken." Moreover, the vmaximum marking interval for each channel is restricted in terms of percentag'er'to there is no amplitude modulation but only time durationof the dots. Moreover, time'duration of the dots ordinarily indicates telegraphc communication. rather .than the other modes` of vcommunication above enumerated. YIn addition, however, the displacement of the bands o f frequency and the interleaving of their .dot components requires that the dots be unscrambled and segregated into ariumber of groups. Even then the message remains unintelligible until all but one of the bands of frequency have been shifted in the frequency spectrum to occupy their original band, and all of the bands must thereafter be combined in order .to provide a replica of the original message. There is also opportunity for rendering the @system more 'secret by changing the Widths of the bandsof frequencies in anonperio'dic fashionyand by'interchangingthe interleaving of the dots of each of the channels vin a .non-periodic fashion.

Thus it is the main object of my invention to provide anevv methodof transmitting intelligence.

Va range lying between fo and f1.

3 amplitude variations into time durations before transmission.

Yet again, it is an object of my invention to provide a receiver embodying a commutator and amplitude converter for transforming a message received in the form of dots of constant frequency to an amplitudeV varying signal representative of telephone or television transmission.

Other objects of my invention will become apparent to those skilled in the art upon the readthe CFVD converters, the outputs of the converters I5, i1 and I9 occur sequentially and the inception of each dot from the converter is spaced ing of the following detailed description,A taken together with the drawings.

In the drawings,

Figure 1 shows, in blockz'dia'lgrammatic forme the essential elements of the transmitter embodying the principles of the methods and apparatus of my invention;

Figure 2 shows, in block diagrammatic forma receiver embodying the methods and apparatus of my invention;

Figure 3 shows, in schematic form and -in somewhat more detail, one of the channels of the transmission system shown in Figure 1;

Figure 4 shows, in somewhat more detail schematically, the commutator distributor and other elements incorporated in the receiver useful with my system; and 1 'Y Figures 5a-5n-show the time relationship in graphical form of the input signal and the wave shapes of the currents Ypassing through the various portions of equipment.

In Figure 1, a Isource of signals I is lfed to a plurality of filters 3, 5 and 1, to separate the frequencies originally present in the source of signals into a plurality of frequency bands. The use cf three bands will be assumed in describing the present invention although, obviously a different number of bands may be employed. Thus, if the vsource of signals includes frequencies between the limits of fo and fs, then the. lter may be a low pass filter, for example, passing the frequencies fo and f1. The filter 5 may be a band pass lter passing the frequencies between the limitsv ofV fr and f2, while filter I may be a high pass lter passing frequencies from f2 and f3. Alternatively, all .of the filters 3, 5, and 'I may be band pass filters. The output'of the filter 5 isthen fed to a frequency transformer 9 to change the range of frequencies between fi and f2 to .a range of frequencies lying between fo .and f1,

it being assumed that the range of frequencies fn and -fi isrequal to the same range of frequencies lying between f1 and f2 and those 'frequencies lying between f2 and fs.

Likewise, the frequencies passed bythe filter 'I are transformed by the frequency transformer II to have their range Changed from fz tofs to A .source of sawtooth oscillations I3 feeds a constant frequency variable duration dot converter I5, and likewise feeds the constant frequency vvariable duration dot converters II and I9 through the phase Shifters 2l and 23, respectively.` Inthe assumed example, where the number of channels is takenfat three, the .phase shifter 2| introduces a shift of 120 of the sawtooth oscillation,` while the phase shifter 23 introduces a phase shift of where Ic is an integer less thanl "n and n is the number of channels. phase shifts between the sa'wtooth oscillator and By introducing. the

a constant time interval between successive dots, The CFVD converter may take the form shown in the Shore et al. Patent No. 2,083,245, and is shown schematically at the right hand side of Figure 3. The operation of the circuit .will be described in somewhat more detail in describing Figure 3.

In order to facilitate an understanding of the operation of the arrangement shown in Figure l, reference is made toFigures 5a through 51a. In these figures the abscissa relates to the time, while the ordinance relates to the amplitude of the energy. In Figure 5a it will be assumed that the envelope 0f the signal energy from the source of signals which has a time variation shown in the curve 5I being made up of energy whose frequency components between the frequency limits fo and f1 have a time variation shown by the graph 53 in .Figure 5b, While the energycomponents lying between the frequencies f1 and fz have a time variation shown in curve 55 of the Figure 5f and whose energy components lying between the frequencies f2 and fa have aA time variation shownrbythe curve 51 in Figure 57'. That is to say,the sum Vof the energy Vcomponents varying with time as shown in the curves 53, 55 and 51, is shown by the curve 5| of Figure 5a.

Consider rst thev energy variation passing through the lter 3 and having a time variation shown by the curve 53 in Figure 5b. In the CFVD converter I5, fed with sawtooth oscillati-ons from thesource I 3, the energy passed by the lter 3 will permit peaks of the sawtooth oscillationsto pass, which, are then converted into square wave dots, the .weight of the dots being proportional to the amplitude of the 4peaks ofthe sawtoothwave passed. Thus, the sawtooth wave energy fed to the converter I5 is shown in Figure 5c. The peaks passed by the converter are shown in Figure 5d, `and are proportional `to the amplitude of the .curve 53 shown in Figure 5b. The resultant peaks are thereafter converted into square dots having lweights which are proportional Vto the peaks as shown in Figure 5e. It will be noted that no dot results for the i'lrstsawtooth Wave since at this point the. amplitudel of energy as shown by the 'curve 53 is Zero. At the midpoint the amplitude ofthe curve 53 `isa maximum and as a result, the whole sawtooth wave is passed and accounts for a square'dot, Ishown in Figure 5e, whose duration is just under one-third of thetime interval required for one cycle of the .satwtooth wave. Similarly, the energy passed by the filter 5 is shown by thecurve 55 in Figure 5f. The sawtooth wave energy 65 is now displaced, one-thirdof a cycle, as shown in Figure 5g, and the peaks passed byl the converter .I`I,.shown as the curve G in Figure 5h., upon conversion take the form of the 'square dots 69,.shown in Figure 52.A

)The energy 'from the iilter 7, when combined with the sawtooth wave 'I I, displacedtwo-thirds The receiver shown schematically in Figure 2 comprises any conventional radio receiver 25 feeding a distributor-commutator 21, which merely segregates the dots into three groups, the first group comprising the dots numbered 1, 4, 7, l and soforth, the dots in the second group constituting those numbered 2, 5, 8, 11 and so forth, while the third group comprises the dots numbered 3, 6, 9, 12 and so forth. The dots of the first group are fed to the amplitude converter Z9 and the amplitude converter vmay comprise, for example, a detector and a low pass filter whose cut-off frequency i5 substantially the same frequency as the frequency fd of the saw-y tooth oscillator |3. `As a result, all the components of the sawtooth oscillator are suppressed and only a DC component is present, whose instantaneous amplitude varies in accordance with the weight of the dots. The second group of dots from the commutator 21 are fed to the amplitude converter 3|, which is similar to the converter 29, to produce an output having an amplitude variation proportional to the dot duration Variation and whose frequency components will lie between the range fu and f1, the same range as that of the converter 29. Similarly, the third group of dots from the commutator 21 are converted into a DC current variation in the converter 33, and occupy the same range of frequencies, fn and f1, asthat of the converters 29 and 3|.

A frequency transformer 35 converts or transforms the frequency range fn to f1 of the cornponents from the converter 3l to components having a frequency range f1 to f2, while the frequency transformer 31 converts the frequency components from the converter 33 so 'that they now occupy the frequency spectrum lying between the lrange f2 and f3. Subsequently, the output of the converter 29 is combined with the outputs from the frequency transformers 35 and 31 so that the output now contains the original frequency components lying between the range fo and fathe amplitude of these componentsl being proportional to the original components of energy present in the source of signals For telephonie communication, the introduction of the phase shifts at the transmitter` by the phase shifters`2| and 23 of Figure l'will not i introduce any noticeable distortion, as it is well known that in telephonic and sound reproduction, the relative phase betweenthe different components is ordinarily undetectable by ear. For television transmission, however, the phase relationship between the various components is of considerable importance, and in this case suitable phase delay may be introduced in the ouiputs of the converter 29 and the frequency trans'- former 35 so as to make the total time delay of transmissionand reception equal for all three channels.

In Figure 3 I have shown in somewhat more detail one of the channels of the transmitter, in order to illustrate the frequency transformer and the CFVD converter. In Figure 3, the elements corresponding to the elements shown in Figure 1 bear the same designation numerals. The source of signals I feeds energy to the band pass filter 5 so that the frequency components f1 to f2 are segregated and passed on to the frequency transformer 9. The frequency transformer 9 is merely a balanced-modulated and low pass filter. The balanced-modulator is of the well known Heising type, `and comprises a pair of tubesA connected in push-pull in their plate circuits and having' its input circuit fed by energy from the filter 5 in push-pull tothe grids of the tubes 39 and 4| through the transformer 43.

Energy from Ythe oscillator 45, whose coincides with the top frequency passed by the filter, is fed in series through the transformer 41 to the grids of the tubes 39 and 4|. The output energy from the balanced-modulator is fed through the transformer 49 to a low pass filter 56, whose pass range is between the frequencies ,fo and f1.

As is well known, the balanced-modulator suppresses the frequency f2 in the plate circuit, so that there is only present frequency components which are the sumand the difference of the fre-` quencies from the filter 5 and the frequency from the oscillator 45. The sum frequenciestherefore, will lie between the frequencies fz plus'fi and f2' plus f2. The difference frequencies will lie between the range of 'f2 minus f2 and f2 minus f1. If the filter 59 is chosen as a low pass filter, only the difference frequencies will be passed, and these frequencies will lie between fn and f1, since it was assumed that the band widths of each channel were equalv and that consequently the frequency f2 is equal to twice the frequency f1. The difference frequency f2 minus'fi is consequently equal to f1. Thus the frequency components passed by the lter 5 and lying between the frequencies f1 and fz are transformed so that they now lie between the frequencies jo and f1, and consequently occupy the same band of frequencies as' those'passed by the lter 3.

The output of the filter 50 is fed to the CFVD converter |1, which comprises a tube 83 biased to cut-off 85, so that the sawtooth wave energy from the oscillator I3 passed through the phase shifter 2| and fed across the resistor 8| is just at the point of overcoming the bias on the peaks of the sawtoothwave. The energy from the filter 50 consequently, when connected in proper polarity, reduces the bias in accordance with the energy from the lter 50 provided by the filter 85, so that the peaks of the sawtooth wave will be passed in proportion t'o the amplitude of the energy from the filter 50..

VAs a consequence, there will appear across the plate resistor 89 triangular pulses whose amplitude is proportional to the instantaneous value of the energy fromthe filter 50. The time duration of the triangular pulses will likewise be proportio'nal to the 'instantaneous amplitude of the energy from the lter 50 in view of the fact that the bases of similar triangles are proportional to the altitude of the triangles. The triangular pulses'from the resistor 489 are then fed to a square'wave amplifier comprising the tubes 93 and |03', which converts the triangular pulses, whose base and amplitude vary, to square Vwave dots of constant amplitude and Whose duration is 'proportional to the duration of the triangular pulses. 'I'he square wave amplifier may be ofthe type disclosed in the Shore Patent No."2,005,l1l. The output of square wave dots may then be fed to the transmitter from the terminals ||I connected-across the output resistor |09.

In Figure 4 I have shown in somewhat `more detail the receiving end of my new system, and incorporating a commutator-distributor, amplitude converters, the frequency transformersand "the final output circuit. In Figure 4, the vacuum tubes VT-I, V'I'-2 and VT--3 comprise the distributor tubes. actuated from the signal input of thenreceiver` fed tothe terminals |l3.` The vactivation of the commutator takes'place'by transfrequency to the rectifier-amplifier tube VZV-23, which,'in

turn, activates the impulse tube VT--25. The in-V co-mingsi'gnals serve 13o-operate cyclically and'sequentially the tubes VT,-|, VT-Z and VT-3 in synchronism with the incoming signals. The c-ommutator is of the Shumard type described in the Shumard Patent No. 2,146,862, as well-as in theV article described Some electronic switching circuits in the May, 1938, issue of -Electrical Engineering at pages 209-220. Consequently, a detailed explanation of the operation of the commutator circuitwill not be given since these circuits are already well known. -It is only necessary to point out that in operation only one of the three tubes of the commutator draws current.

at any instant, while the other two tubes are cut off.

Assuming that the incoming pulse has'activated the tube VT--3, a positive pulse from the tube VT-'3 is Aapplied to the input grid of the limiter tube V'I-6, the pulse being derived from the drop in potential across the cathode resistor R-Q. .As a result; plate current in the tube VT-- nows through the resistor R-|6, producing a potential drop which causes the grid of the second half of the tube 'VT-6 to become inactive with respect to its cathode. The inactive potential on this grid blocks the flow of plate current on the second half of the tube VT-6, reducing the potential drop acrossr the resistor Rf-2I to Zero. This permits the push-pull stage, comprising the tubes |3| and |33, to act as an amplifier for the incoming lsignal which is applied to the grids of these tubes through the transformer |2I, since the cut-off bias previously ori the grids and Obtained from across the resistor R-Zl has been removed. The amplified signal is thereafter passed through the transformer ,IM to the rectier 41, and the output obtained across the resistor |48 is fed to a low pass lter |53. The low 4pass lter |53 has a cut-off frequency of fd so as to suppress the dot frequency components and pass only the D. C. components.

The D. C. components will vary in amplitude in accordance with the time duration of the dots and thevariations of the D. C. component will have frequency components lying between the frequencies fo and fr. Theseffrequency components are then transformed by a frequency transformer comprising the balanced-modulator |59 and the oscillator |61 in a similar fashion to that described in connection with Figure 3.- The oscillator ll has a frequency ,f3 and consequently the sum and difference frequencies at the output of the balanced-modulator |59 will be fs plus fo, f3 plus f1, f3 minus fo, and f3 minus f1, Remembering that f3 is three times .the frequency of fi, it will be readily apparent that passing the output of the balanced-modulator |59 throughv the low pass filter |55 will result in only those frequencies lying between f2 and fa, passing to the output terminals |61.

'Ihe next impulse received will cut off lthe tube VT-l, rand activate the tube VT-2, which in turn will provide kan output Vfrom the low pass lter |63V to the output-terminals |67 in the same fashion'as described for theprevious channel. Thereafter, the next impulse will pass,A through the channel activated byV-T-l Atovprovidean output from thelowpass filter-.|49 with frequency componentsy lying between ,fo and f1.

Since these frequency components already correspond to thegassociated, channel at the transmitter, it is-:uenecesSer-y to'shiit these@ frequenta 8 so that ,nelbalanced-modulatorv is-provided for this channel. The combination, therefore, of the output from the low pass filter |49 together with the outputs of the filters |63 and |65 will provide across the terminals |51 energy components whose .frequencies will lie between the limits of ,fo

and f3, that is to say, the identical frequency'-l range of those of the original signals.

It is to be noted that in transmitting the square dots, the maximum duration of the dots was restricted to'just underv the time interval of onethird of the sawtooth period. Thisis necessary to insure that a space occurs between successive dots in order to properly actuate successive channels by the distributor-commentator. If the space between dots were omitted, it will be readily seen that switching of the channels could not take place since the sequential operation of the commutator depends ontermination and initiation of the dots. For-this reason, it is desirablevto see that the bias of the CFVD converters is adjusted to just pass the peaks of the-sawtooth wave, so

that at all times there are transmitted dotsfof very light weight of say, for example, 1% of the time duration of one sawtooth oscillation.

It will be appreciated, of course, that it is essential that the incoming impulses activate the proper channel.l This can be readily achieved by operating the switch ||4, that to open and close the switch rapidly until the proper phase is obtained. Conversely, a phasing signal may be sent comprising along dash, and the switch opened and closed until the proper tube operates', which will thereafter be kept in an operating position by the long dash..

. From the above description, it, of course, will be apparent that many and varied modifications of the invention may be made without departing from the general principles described and outlined hereinabove, and I, therefore, believe myself to be entitled to make any and all of these modifications such as would suggest themselves to those skilled in the art to which the invention relates, provided, of course, that such modifications and changes fall fairlywithin the spirit and scope of Lthe invention as set forth in thehereinafter appended claims. j

Having now described my invention, what I claim is: f 1 f l.. The method of signaling which comprises the steps of producing electrical signals having frequency components lying between .two predetermined limits of frequency, separating thefrequency components into a plurality of bands of frequency contiguous with each other, shifting all but one of thefbands of frequency tor occupy the same frequency range as the frequency range of the unshifted band of frequencies, converting each bandfof frequency components into constamt-frequency `variahle-duration pulses and cyclically and sequentially transmitting pulses of each of the plurality of bands.

2. The methodv of reproducing signals transmitted in the form ofV Asequentially transmitted pulses of constant amplitude and variablev time duration representative of a single train'of energy having frequency components lyingbetween two predetermined limits of frequency which includes the steps of receiving the transmitted energy, distriibuting thelreceived energy into aplurality of channels, converting the received pulse energy in each channel into variable amplitude energy, shifting the frequency range of the energy componventsl in all but one :of the channels, and com- 9 bining the shifted energy components with the unshifted energy components.

3.- The method of signaling which comprises the steps of producing electrical signals having frequency components lying between two predetermined limits of frequency, separating the frequency components into a plurality of bands of frequency contiguous with each other, shifting all but one of the bands of frequency to occupy the same frequency range as the frequency range of the unshifted band of frequencies, converting each band of frequency components into constant-frequency variable-duration pulses, the duration of said pulses being substantially proportional to the amplitude of the energy within the respective bands of frequency, and cyclically and sequentially transmitting pulses ofl each of the plurality of bands.

4. The method of reproducing signals transmitted in the form of sequentially transiriitted pulses of constant amplitude and variable time duration representative of a single train of energy having frequency components lying between two predetermined limits of frequency which includes the steps of receiving the transmitted energy, segregating said pulses into a plurality of groups, distributing the segregated groups into a plurality of channels, converting the pulse energy in each channel into variablev amplitude energy, shifting the frequency range of the energy components in all but one of the channels, and combining the shifted energy components with the unshifted energy components.

5. The method of signaling which comprises the steps of producing electrical signals having frequency components lying between two predetermined limits of frequency, separating the frequency components into a plurality of bands of frequency contiguous with each other, shifting all but one of the bands of frequency to occupy the same frequency range as the frequency range of the unshifted band of frequencies, converting each band of frequency components into constant-frequency variable-duration pulses of energy, cyclically and sequentially transmitting said pulses of energy of each of the plurality of bands, receiving the transmitted energy, distributing the received energy into a plurality of channels,` converting the received pulse energy in each channel into variable amplitude energy, shifting the frequency range of the energy components in all but one of the channels, and combining the shifted energy components with the unshifted energy components.

6. Signaling apparatus comprising means for producing electrical signals having frequency components lying between two predetermined limits of frequency, means for separating the frequency components into a plurality of bands of frequency contiguous with each other, means for shifting all but one of the bands of frequency to occupy the same frequency range as the frequency range of the unshifted band of frequencies, means for converting each band of frequency components into constant-frequency Variableduration pulses, and means for cyclically and sequentially transmitting pulses of each of the plurality of bands.

'7. Signaling apparatus comprising means for producing electrical signals having frequency components lying between two predetermined limits of frequency, means for separating the frequency components into a plurality of bands of frequency contiguous with each other, means for .Shifting all but one oi the bands of frequency to occupy the same frequency range as the frequency range of the unshifted band of frequencies. means for converting each band of frequency components into constant-frequency variable-duration pulses, the duration of said pulses being substantially proportional to the amplitude of the energy within the respective bands of frequency, and means for cyclically and sequentially transmitting pulses of each of the plurality of bands.

8. Signaling apparatus comprising means for producing electrical signals having frequency components lying between two predetermined limits of frequency, means for separating the frequency components into a plurality of bands of frequency contiguous with each other, means for shifting all but one of the bands of frequency to occupy the same frequency range as the frequency range of the unshifted band of frequencies, means for converting each band of frequency components into constant-frequency variable-duration pulses of energy, means for cyclically and sequentially transmitting said pulses of energy of each of the plurality of bands, means for receiving the transmitted energy, means for distributing the received energy into a plurality of channels, means for converting the received pulse energy in each channel into variable amplitude energy, means for shifting the frequency range of the energy components in all but one of the channels, and means for combining the shifted energy components with the unshifted energy components.

9. Receiving apparatus for reproducing signals transmitted in the form of sequentially transmitted pulses of constant amplitude and variable time duration representative of a single train of energy having frequency components lying between two predetermined limits of frequency comprising means for receiving the transmitted energy, means for distributing the received energy into a plurality of channels, means for converting the received pulse energy in each channel into variable amplitude energy, means for shifting the frequency range of the energy components in all but one of the channels, and means for combining the shifted energy components with the unshifted energy components.

10. Receiving apparatus for reproducing signals transmitted in the form of sequentially transmitted pulses of constant amplitude and variable time duration representative of a single train of energy having frequency components lying between two predetermined limits of frequency comprising means for receiving the transmitted energy, means for segregating said pulses into a plurality of groups, means for distributing the segregated groups into a plurality of channels, means for converting the pulse energy in each channel into variable amplitude ener-gy, means for shifting the frequency range of the energy components in all but one of the channels, and means for lcombining the shifted energy components with the unshifted energy components.

11. A signaling system comprising a source of signals having energy components whose frequencies lie. between an upper and lower predetermined limit, a plurality of filters connected to said source of energy, a constant-frequency 0 variable-duration dot converter connected to the output of one of said plurality of lters, a frequency transformer connected to each of the other of said plurality of filters, a constant-frequency variable-duration dot converter connected to each of said frequency transformers,

11 a common source of 'savvtoothwave energy Vconnectedto all of said constant-'frequencyvariableduration d'ot converters, and means for'co-mbining the output of all of said converters to feed to a common 4transmission channel.

I2. A signaling system comprising 'a source of signals having energy components Whose frequencies lie between 'an upper'and lower predetermined limit, 'a plurality 'of lters connected to said source of energy, a constant-frequency variable-duration dot converter connected 'to the output of one of Said plurality of filters, a fr'equency transformer connected to each of the other of said plurality of filters, a constant-frequency variable-duration 'dot converter connected to each 'of "said 'frequency transformers, a common source of sawtooth Wave energy connected to all of 'said constantfrequency variable-'duration dot converters, a phase shifting net'w'ork connected in the 'connection from the sawto'o't'hwave'oscillator to each of the converters coiinected't'o Vafrequency Ymultiplier, and means 'forcombihingtheutput'of all of said converters to'f'ee'dto a common transmission channel.

13. AA signalrec'eiver comprising means 'forreeeiving electrical signals in the form'of sequentially transmitted pulses of constant 'amplitude andvariable time 'duration representative of a single train'of energy having 'frequency componente lying between "ttvo predetermined limits of frequencies, "a commutator for distributing the receivedpulses into`a plurality'of channels, a'detect'or in 'each of saidpluralityof channels, an amplitude converter "connected to each of said detectors, Va 'frequency "transformer con- 12 nected to each amplitude converter but one, and means to combine the output from all of the 'frequency transformers With the output from the said one amplitude'converter.

5 14. A signaling system comprising a source of signals having ener-gy components Whose frequencies lie between an upper vand lower predetermined limit, a plurality of lters connected te said source of energy, a constant-frequency lo variable-duration'dot -converter connected tothe output-'of one of said plurality of filters, a frequency transformer connected to yeach Aof the other of said plurality of filters, -a constant-'frequency variable-duration dot converter con- 15 lnected to each of said frequency transformers,

`'a1/common source of saWtooth Wave energy connected to al1 of said'constant-frequency Variableduration dot converters, a phase shifting-network connected in the connection from the sav/tooth 20 'wave oscillator to -each of Ythe converters con- `nected'to a frequency multiplierfmeans vfor-comnbining the output of all of -said converters to feed to a common transmission channel, means for transmitting the combined Aoutput pulses,

25 means yfor receiving the transmitted pulses, a 'commutator for distributing ythe received pulses into-aplurality off-channels, a detector nin each of said plurality of channels, an Y amplitude Iconverter'eonnected to-eaeh of l said detectors, Aa fre- 30 -Yquency 'transformer connected to each -amplitude converter but one, and Ameans to `combine the output from all of the frequency transformers with the output from the -said-one Vamplitude converter.

Yl-IENRY SHORE.

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