March 17, 1953 F. GRAY 2,632,058 PULSE CODE COMMUNICATION filed Nov. 13, 1947 4 Sheets-Sheet 1 FIG./
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INVENTOR F. GRAY ~~C.)/~ ATTORNEY Marcb 17, 1953 F. GRAY 2,632,058 PULSE CODE COMMUNICATION Filed Nov. 13, 1947 4 Sheets-Sheet 2
FIG.2 FIG.2A REFLECTED BINARY CONVENTIONAL BINARY CODING MASK CODING MASK(PRIOR ART)
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INVENTOR F. GRAY BY ~"""'1 ~. )IJ ATTORNEY March 17, 1953 F. GRAY 2,632,058 PULSE CODE COMMUNICATION
Piled Nov. 13, 1947 4 Shee~s-Sheet 3
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INVENTOR F. GRAY BY NAAAyc.)JJ ATTORNEY March 17, 1953 F. GRAY 2,632,058 PULSE CODE COMMUNICATION Filed Nov. 13, 1947 4 Sheets-Sheet 4
INVENTOR F. GRAY BY t.J~c.JIJ ATTOBNEY Patented Mar. 17, 1953 2,632,058
UNITED STATES PATENT OFFICE 2,632,058 PULSE CODE COMMUNICATION Frank Gray, East Orange, N.J., assignor to Bell Telephone Laboratories, Incorporated, New York, N.Y., a corporation of New York Application November 13, 1947, Serial No. 785,697 16 Claims. (Cl. 179-15) 1 2 This invention relates to pulse code transmis der control of the signal to a particular aper sion and particularly to the coding of a message ture row and thereupon swept laterally along signal in a novel code and to the decoding this row, a train of current pulses may be drawn thereof. from the collector whose location on the time In communication by pulse code transmissions 5 scale is in accordance with the arrangement of the instantaneous amplitudes of a message to the 1's and O's in the binary number whose value be transmitted are successively sampled and is equal to the value of the signal sample being each of the successive samples is translated into coded. a code group of on-or-oft' pulses. By reason of It is a characteristic of the conventional binary the on-or-oft' character of the pulses, such a 10 number notation that a value change of unity code is denoted a binary code. The number of may be reflected in the binary number nota pulse positions in a code group is the same from tion by a simultaneous change in several of the group to group. With five such positions the digits. Thus, for example, with four digits the code is a 5-digit binary code. With seven it is number seven is represented by 0111 while the a 7-digit binary code; and in general, with n 15 next number, eight, is represented by 1000. In such positions it is an n-digit binary code. A the course of changing the value by one unit, code pulse group of n pulse positions may con each of the four digits has been changed. tain any number, from 0 to n, of "on" pulses. This characteristic of the conventional binary In the conventional n-digit binary code, the number notation is duplicated in the coding mask number and arrangement of pulses is in accord 20 of the Italian patent above referred to, and it is ance with the conventional binary number no a consequence of the resulting arrangement of tation. Thus, for example, with three digits, the apertures that a wander of the beam in the the number five is written in the conventional course of its lateral sweep from the correct aper binary number notation as 101. Correspond ture row to the row immediately above or below ingly, in the conventional 3-digit binary pulse 25 it, may result in a coding error which is far code, the pulses occur in the time sequence greater than the beam deflection error. Various P, -, P, where "P" stands for an "on" pulse arrangements have been suggested for reducing and "-" stands for an "oft'" pulse; i. e., a blank this coding error by constraining the cathode pulse position. beam to start its sweep at the correct row and In Italian Patent 437,300, published June 30, to remain there throughout the sweep. Arrange- 1948, there is described an instrument for trans 30 ments of this kind are described in articles pub lating message signal samples into code pulse lished in the Bell System Technical Journal for groups in the conventional binary code. In brief, January 1948, val. 27, pages 1 and 44, which de it comprises a cathode beam tube having a cod scribe the coding tube, in detail. Individual fea tures of the apparatus are claimed in Patent ing mask, an electron gun for projecting an elec 35 tron beam toward the mask, a collector anode 2,458,652, issued January 11, 1949, toR. W. Sears; for receiving electrons which pass through the Patent 2,463,535, issued March 8, 1948, to G. mask and deriving pulses from them, means for Hecht; and in Patent 2,473,691, issued June 21, deflecting the cathode beam in one direction 1949, to L. A. Meacham. All such arrangements along the mask to a location proportional to 40 involve complexity of apparatus in various de the signal sample amplitude, and means for grees. sweeping the beam in a perpendicular direc It is a principal object of the present invention tion across the mask between successive sample to reduce the coding errors in a pulse code trans controlled deflections. As currently employed, miss~on system. A more specific object is to pro- the mask comprises a rectangular array of aper 45 vide a pulse code, and a correEponding coding tures arranged in n columns and 2n rows, where mask, in which the coding error is never greater n is the number of digits of the code. Each than the beam deflection error. aperture row corresponds to a unique value of Another object is to simplify the manufacture the signal-controlled beam deflection. The aper of a coding mask. tures of the various rows are located in con- 50 The above objects are attained in accordance formity with the location of the 1's in a tabula with the invention bY the selection of a novel tion of successive binary numbers, while the form of the binary pulse code which differs from blank portions of the mask are located in con the conventional form by virtue of a rearrange formity with the O's in the same tabulation. ment of the pulses of the various pulse groups Thus, when the cathode beam is deflected un- 55 in such a way ·that the sequence of "on"-pulses 2,632,058 3 4 and "off"-pulses which form a pulse group rep columns, by cutting the tabulation at any horl re2enting g particular signal amplitude differs in zantal line and placing the upper part below the only one pulse position from the sequences repre lower one; by changing all the 1's of any column senting the next lower amplitude and next higher to O's and all the O's to 1's; by construction from amplitude. The new code is no longer similar ;) the conventional binary code by a modification to the accepted binary number notation. When of the reflection process, and so on. Some of it is emto died in a coding mask, the arrangement these forms offer special advantages over others. of the auertmes of any one row differs from that The coding of signals into them uresents no ad of the rows above and below it in not more than ditional prcblem. The decod·ng-can be carried one aperture. The resulting mask has certain 10 out in various ways by suitable adaptations of v9Juable auxilary properties and aspects. First, the decoding apparatus and processes described the smallest apertures, that is to say the aper J::elow in detail for the reflected binary code in hues of the various rows in the column of least its primary form. digital significance, are twice as large as the The invention will be fully apprehended from auc•·tures of the conventional binary code mask. 15 the following detailed description of preferred Thi; makes for ease of manufacture. Second, embodiments thereof, taken in conjunction with all of the apertures of the mask, with the .sole the appended drawings in which: exceution of the single aperture of greatest digi Fig. 1 is a schematic diagram of coding ap tal significance, are symmetrically arranged about paratus in accordance with the invention; a transverse center line. This permits treating 20 Fig. 2 is an end view of the coding mask of the largest digit aperture as an index of polarity Fig. 1 drawn to an enlarged scale; only, rectifying the wave to be coded, sampling Fig. 2A is a similar view of a conventional cod the rectified wave, and coding the samples using ing mask; only one half of the coding mask. At the price Fig. 3 is a schematic circuit diagram of ap- of some increased complexity of associated ap 25 paratus for translating incoming reflected binary uaratus, this greatly reduces the physical dimen code purse groups into conventional binary code sions of the coder tube itself. Third, for signals pulse groups and for decoding the latter and re of norms:.l average amplitude range, the beam de producing the decoded values as a signal; flections seldom extend beyond the aperture of Fig. 4 is a o:chematic circuit diagram of an al- the colm:m of second greatest digital Eignificance, 30 ternative to Fig. 3; so that in the resulting coded signal, the
primary one. Again, the initial process of build The formulae for converting from the conven- ing up the code by reflection may be modified, 25 tional notation to the reflected notation are giving two alternatives for the 1-digit code, four for the 2-digit code, and so on. The four alter natives for the 2-digit code are tabulated below. (Mod. 2) {Mod. 2) Of these the first is the primary one discussed above, the others being variants. 30 (Mod. 2) (Mod. 2) (2) ' . I First Second Third Number I nmary Variant Variant Variant (Mod. 2) ------1·------(Mod. 2) 35 (Mod. 2) ZeroOne ______------_ 00 10 01 11 01 11 00 10 (Mod. 2) 'l'wo ______11 01 10 00 (Mod. 2) Three_ ------10 00 11 01 In both sets of formulae, the proviso "Mod. 2" For illustrative purposes, the primary reflected 40 means that all even sums are written "0" and all binary code will henceforth be adhered to. odd sums are written "1." Returning to Fig. 1, whenever the electron The foregoing general formulae are evidently beam II passes through an aperture of the mask reduced to those for 7-digit codes merely by 15, it strikes the collector anode 14 and gives noting that, for seven digits, Rs ... Rn and rise to a current pulse in the output conductor 45 Cs . . . Cn are zero. and to a voltage pulse across the loading resistor As is well 'known, the value of a number is 27 and on the outgoing line 40. Because these obtained from its representation in the con pulses are due to electron current they are nega ventional code by weighting the various C's in tive in sign. Furthermore, they may be de proportion to 2d-1, where d is the digit num- graded in various ways and for various causes. 50 ber, and adding the results. Thus, for the num Before transmission they are preferably regen ber thirty-eight, which in the 7-digit conven erated, for example, by a gater-slicer circuit ·tional binary code is written: Thirty-eight = which may be of the type described in the Bell 0100110, System Technical Journal publications above re ferred to. To this end a pulse regenerator circuit :;;, 37 is show:..1 schematically and it is supplied by way of a conductor 33 with gating pulses orig inating in the basic pulse generator. (3) The pulses as thus regenerated are still nega tive in sign and may be transmitted in that con- 60 dition. However, to facilitate the description of the receiver apparatus, it is preferred to in vert the pulses in polarity, thus rendering them Thirty-eight all positive in voltage. This may be accomplished in any convenient way, for example, by an am- 65 Applicant has discovered that a number may plifier 39. be obtained from its representation in the re At the receiver station, the incoming signal flected binary code in its primary form by ·a ·re is amplified and demodulated as required, by lated but different process, namely, by (a) weight means not shown, to recover reflected binary code ing the various R's in proportion to 2d-l, (b) pulses. These are now to be translated into 70 changing the signs of alternate non-zero R's, message signal samples for reproduction, either starting with the second, ·and (c) adding the re directly or by preliminary translation into con sults. The second step is equivalent to multiply ventional binary code and decoding the latter ing by (-'1) 5 , where Sis the number of non-zero by conventional methods and means. digits in the symbol with digit numbers greater The .formulae which, for any number, relate 75 than d. Thus, for the number thirty-eliht, 2,632,058: 9 10 which in the 7-digit reflected binary code is writ. system there disclosed comprises a differentiat ten: Thirty-eight=OllOlOl, ing circuit 54, a rectifier 55, a band-pass filter 56
0 tuned to the basic pulse frequency and a pulse 7( =0) X (21-1) X ( -1 ) =Zero ] R 0 shaper 51 in tandem. As fully described in that R 6( = 1) X (2L 1) X ( -1) = +Sixty-three 1 IS application, this arrangement of apparatus re R5( = 1) X (2L 1) X ( -1) = -Thirty-one 4 produces the basic pulse frequency of the trans R4 (=0)X(2 -1)X(-1)2=Zero (4) R3( =l) X (::03-1) X ( -1)2= +Seven mitter pulse generator 26. This pulse frequency R 2( =0) X (Z2-1) X ( -1 )3=Zero may operate a frequency divider 58 of which 3 R 1 ( = 1) X (21-1) X ( -1) = -One the frequency ratio is equal to the number of 10 digits of the code. Thus, with the 7-digit code, Thirty-eight the frequency divider should produce output Figs. 3 and 4 show alternative forms of receiver pulses whose frequency is one-seventh of the apparatus in which incoming reflected binary frequency of the basic timing source. A step code pulse groups are first transformed into con down multivibrator is a suitable instrument for ventional binary code groups by realization of 15 the purpose. Its output pulses are next squared the Formula 1, whereupon the resulting conven and standardized in form by a shaper circuit tional binary code pulses are conventionally de whose output, in turn, operates the distributor. coded. Fig. 5 shows receiver apparatus which In the symbolic representation of the figure, the evaluates incoming reflrcted binary code pulse contact arm rotates at one half the rate of the groups directly in accordance with the Formula 20 driving group frequency pulses. 4 into message signal samples, without resort to Application of the positive voltage of the bat-· the intermediate translation process from code tery 52 to the control grids of the tubes 46, 46' to code. Referring first to Fig. 3, the incoming of the two flip-flop circuits in sequence by the reflected binary code signal, after such prelim distributor 53 returns each flip-flop circuit to inary demodulation and amplification as may be 25 its initial condition at the conclusion of the pulse required, appears at the input terminals of the group which it has just translated and holds receiver proper, schematically indicated by a it in this condition until, after one pulse group broken line 41 as reflected binary code pulses. period, the voltage is removed by movement of For best results they are preferably regenerated, the rotating arm 50 of the distributor to the op- for example, by a gater-slicer circuit 42 of any 30 posite segment. Thereupon the positive voltage suitable type, whereupon they are routed to one rapidly leaks off to ground by way of the var or more translating networks, the number be ious resistors connected to the grid of the flip ing dependent on the rapidity with which such flop circuit. Thus, the two flip-flop circuits are translating networks may act. Thus, in Fig. 3, enabled in alternation, one being disabled while two such networks are employed and the regen 35 the other is enabled. Furthermore, each is re erated pulses are applied to them in parallel by turned to its initial condition at the instant it way of coupling condensers 43, 44. Each trans is disabled, thus preparing it to receive a later lating network may comprise a so-called "flip pulse group. flop" circuit, namely, a pair of triodes 45, 46 in In order that the alternate enabling and dis- which the anode of each is connected by a di 40 abling of the flip-flop circuits shall take place rect current path to the control grid of the other. between successive incoming code pulse groups, Appropriate operating biases may be applied to and that each flip-flop circuit shall receive an the control grids by way of voltage dividers. entire group, and not portions of two groups, Thus the control grid of tube 46 receives its bias the phase of the movement of the distributor from a source 51 by way of resistors 47, 48, and is 45 arm 60 must be correct, as well as its speed. Its returned to the negative terminal of this source phase may conveniently be controlled by inclu by way of resistors 49, 50. Such a circuit has sion of an adjustable phase shifter 61 in the two stable rest conditions, in each of which one distributor control path. As this device is ad tube is conductive while the other is not. On justed continuously, a position will be found at the application of a pulse to the grids of both .:,u which the reproducer output is intelligible. For tubes, the condition is reversed, and remains re other positions it is unintelligible because each versed until the application of the next pulse, flip-flop circuit will be translating incomplete whereupon it returns again to the first condi portions of two code groups. The adjustable tion. Thus, for an incoming pulse wave form as phase shifter 61 is thus, in effect, a framing indicated at A, the output wave form, namely, ().) controller. Other more elaborate framing means the wave form of the potential of the anode of may, of course, be employed if preferred. the right-hand tube 46 is as indicated at B. The output voltage of each of the flip-flop For reasons which will be explained below, it circuits tlS, 46' is next gated at the basic pulse is preferred to restore the flip-flop circuit 45, frequency by a regenerator 62, 62' which may 46 to its initial condition at the conclusion of GO again be similar to that described in the afore each pulse group. To this end the control grid mentioned application of L. A. Meacham. The of the right-hand tube 46 is supplied with a two regenerators operating respectively on the positive voltage pulse, derived, for example, from output pulses of the two flip-flop circuits may a battery 52, at the pulse group frequency, by be supplied with control gating pulses at the way of a commutator or distributor 53 which is tl5 basic pulse frequency by way of a conductor 63. driven at the appropriate speed. The distrib The resulting wave form at the output ter utor may be of any suitable type, preferably elec minals uf the regenerator is· indicated at .C. tronic. A particularly suitable system for ob Comparison of the Formulae 1 with the fore taining the distributor driving pulse rate from going operations will reveal that this wave is the incoming pulse tntin is described and shown iO now in the form of the conventional binary pulse in the Bell System Technical Journal publica code, and it may therefore be translated into tions above referred to and is claimed in an ap signal samples for application to a reproducer plication of ..T. G. Kreer and E. Peterson, Serial 64 by decoders 65, 65', whose outputs are col No. 776,280, filed September 26, 1947, now Patent lected turn and turn about by a distributor 66, 2,527,638, issued October 31, 1950. In brief the Hi driven in synchronism with the distributor 63. 2,632,068 11 12 Suitable decoder apparatus is described in Good of a distributor 53 to a restoring and disabling all Patent 2,449,467, issued September 14, Hl48. circuit comprising a triode 81· whose anode and It is the function and purpose of the flip-flop cathode are connected across the condenser 70 circuits of Fig. 3 to produce a change in an out of the pail and dipper circuit, while its control put circuit in a specified direction on the arrival 5 grid. is pulsed positively by the output of the of the first pulse of an incoming reflected binary distributor 53. Thus, application of a positive code pulse group; to remain quiescent until the pulse, for example, to the upper triode makes the arrival of the next pulse and thereunon to pro latter highly conductive so that its "pail" con duce a change in the opposite direction; to re denser 70 cannot hold any substantial charge. main quiescent again until the arrival of the 10 Under these conditions, application of incoming third pulse and thereupon to produce a change code group pul~es to the upper pail and dipper in the first direction, and so on. Other appa circuit are ineffectiYe to deflect the cathode beam ratus than the fiip-flop circuit is possible, and l1 of the upper translating tube 74. During this Fig. 4 shows an alternative to the system of Fig. time, however, the lower triode 81' is held well 3 in which this function is performed by the 15 below cut-off by grid rectification due to the combination of a rectifier circuit and a spe grid condenser 82' and resistor 83' in combina- cially constructed cathode ray tube. The in tion so that application of incoming code pulses coming reflected binary pulse code group, which to the lower pail ~md dipper circuit 10', ll ', 12', again may have the wave form shown at A, is results in stepping the condenser voltage by equal applied to a network comprising a condenser 20 negative steps and therefore deflecting the cath 10, a diode rectifier 11 and a constant current ode beam of the lower translating tube 74' along device such as a saturated pentode am')lifier 12. the translating mask in the manner described As is well known such a circuit orerates in the above. P:-t the termination of this code group, manner of a "pail and dipper" circuit supplying the rotatmg arm 60 of the diotrihutor 53 makes standard increments of charge through the con- 25 contact with the low·er distributor segment and denser 70 upon the arrival of each pulse of the opens the circuit from the battery 52 to the upper incoming pulse code group. Therefore the con distributor segment. Thus the upper pail and denser voltage rises in substantially rquql steps, dipper circuit 10, 71, 12 is enabled while the one step for each incoming pulse. The con lower pail and dipper circuit is returned to its denser wave form is indicated at B. 30 initial condition and disabled. This stepned condense1· wave form is then :ou The resulting translated pulse code groups may pliecl. to vert1ca1. rleflectinc; elements 73 of a cath now be supplied to individual regenerating cir ode beam tube 74 which may coT"'prise an elec cuits and decoders in the manner described above tron gun 75 and a collector anode lS of conven in connection with Fig. 3. Alternatively, they tional tvre and having. interposei in the path of 35 may be applied in alternating sequence to a sin the cathcde beam 11 between the ele,-tron gun gle regenerator 85; to which gating pulfes are 75 and the collector anode 76, a mRslt 18 of spe aPr:lied at. the basic pulse frequency by way of cial configuration. This ma.ck comm·ises a verti a conductor 86 and thence to a decoder 81 which cal array of apertures, each s:oparated frc-m its may be of any suitable type and serves to trans- neighbors by a distance equal to the aT'erture 4.0 late the resulting sequence of conventional binary height. For :>" 7-dic;it rode, four apertures are pulse code groups into a message for reproduc-. reo.uired. separated by three sPaces. Deflection tion in a reproducer 88. bias means, such as an adiustable battPrv-poten In. the Formulae 1, each digit of the trans tiometer combination 19 is inclur1ed in the circuit lated conventional binary code is determined in of the vertical deflection elements 13 and is ad- . part by the most significant digit of the re 15 flected binary code, e. g., Cs, C5, , , justed so that the undeflected beam po~ition lies c •. c3 c2 c1 on the lT'ask 78 just below the fir.st aperture. are all dete:mined in part by R7. By the same The sensitivity of the tube 74 for beam deflec to:::en, the apparatus of Figs. 3 and 4, which carry tions is adiusted in any desired manner so that out the. operations required by the::e formulae, is u~able. to translate correctly until the most sig, a change of one step in the voltage of the con- 50 denser 70 moves the beam 71 upward along the ~Ificant. reflected binary code pulse of each group mask 18 from its rest position to anproximately Is at hand: .To avoid complexity of apparatus, the center of the first aperture, while the next therefore, It 1s Preferred, when translating from step moves it to the blank portion of the mask reflected binary code to conventional binary code, that the. most significant digit pulse of each group which separates the first aperture from the sec- 55 ond, and so on, each voltao:e step moving it from be the earliest received, and the least significant a blank :;pace to an aperture or from an aper the last. It is for this reason that, at the trans- mitter, the coding mask of Fig. 2 is oriented with ture to a blanl~ space. With this construction, voltage pulses appear in the circuit of the col respect to the cathcde beam sweep so that the lector anode 76 and across the output loading ?earn cro.sses the seventh aperture column first 60 1n. the course of its sweep and the first column resistor which. have the characteristics of the last. curve C, namely, a voltage change in one direc Fig. 5 shows a system for translating incoming tion for the first pulse and a like change in reflected binary code pulse groups directly into the opposite direction for the next pulse, and messa~e signal saJ~ples without first translating w~ M them ~nto conv.entwnal binary code pulse groups To allow time for the pail and dipper circuit to as an m_termed1ate step. This system requires no return to its initial condition, and for the cathode resto.r~twn of the translator circuit to its initial beam of the translating tube to return to its initial conditwn at the c?nclusion of a code pulse group position at the foot of the translating mask, two and therefore a s~ngle translator circuit may be lilm systems of pail and dipper circuit and trans- 70 employed. Incommg reflected binary code pulses lating tube are provided. Also pulses of all pulse ap?ear on the incoming line as before and, after code groups may be applied to both systems in be:ng r~~ex:er~te~l, are applied to a flip-ftop cir parallel while pulses of code group frequency, de cmt wh1cn 1s snmlar to that of Fig. 3, except that rived in the manner deocribed above in connection the group frequency pulsing conductor which re with Fig. 3, are applied from a battery 52 by way 75 stores the fiip-flop circuit of Fig. 3 to its initial 2,632,068; 13 14 condition at the conclusion of a code group is the addition may be positive or negative, in de omitted. The incoming pulses A are applied to pendence on whether the pulse of greatest digital the grids of both tubes 90, 91 together and the significance is positive or negative. However, output voltage is taken from the anode of one negative sums are converted to positive sums by tube 91, just as before. The output voltage, 15 the rectifier I DO, while positive sums are unaltered therefore. has the wave form of the curve B if, by the rectifier I DO. The result is a sequence of prior to the first pulse of the group, the right pulses which recur at the pulse group rate. They hand tube 91 was conductive; i. e., if the initial are in fact proportional to the samples of the condition of the circuit was the same as the ini original message signal and can therefore be ap- tial condition of the flip-flop circuit of Fig. 3. 10 plied without further change to a reproducer I 0 I. On the other hand, if at the commencement of An adjustable phase shifter 61 is included in the pulse code group A, the initial condition of the gating pulse conductor which brings group the flip-flop circuit were the reverse, namely, that frequency pulses to the sampler 99. As this de the left-hand tube 90 was conductive, then the vice is adjusted continuously a position will be output wave form would be inverted with respect 15 found at which the output of the reproducer is to the wave form, curve B. intelligible. For other positions it will be un The output voltage of this flip-flop circuit is intelligible because the sampling pulse occurs at next differentiated, for example by a combination an instant at which the pulses of a single pulse of a condenser 92 and a resistor 93 or by any de code group, brought into time coincidence by the sired differentiating circuit, to give a sequence of 20 respective delay devices 95a, 95b, etc., are not positive and negative pulses having the form of present in the amplifier output. the curve C. This pulse sequence is in turn In contradistinction to the code-to-code trans shaped, by any suitable means, schematically in lators of Figs. 3 and 4, the direct translator of dicated by the block 94, to give substantially rec Fig. 5 is, with a small modification, equally well tangular waves as in the curve D. It will be ob 25 adapted to receive and translate reflected code served that pulses of this curve D are substan pulses in which the first pulse of each group to tially identical with those of the incoming re arrive is the pulse of least digital significance and flected binary code pulses with the exception of the last to arrive is the pulse of greatest digital the fact that alternate pulses are inverted in po significance. This would be the arrival order, if, larity. 30 in Fig. 1, either the direction of sweep of the This pulse sequence is now applied to a group cathode beam II or tr1e columnar arrangement of delay devices 95a, 95b, etc. in number one less of the coding mask ~ 6 wel'e reversed. To rear than the number of digits of the code, in parallel. range the apparatus of Fig. 5 to receive reflected The output terminals of these delay devices are binary code pulses in the reverse order of their in turn connected to individual attenuators 96a, 35 digital significance and translate them into mes 96b, etc. whose conductances are proportional to sage signal samples, it is only necessary to inter the numbers 1, 3, 7, 15, 31 and 127. The outputs change the delay times with respect to the nu of these attenuators are paralleled and applied to merical weightings; e. g., connect the longest de the input terminals of an amplifier, preferably. a lay device 95 to the lowest conductance 96, the voltage feedback amplifier which may comprise 40 next longest delay to the next lowest conductance, a triode 91 whose control grid is connected to its and so on, finally connecting the shortest or zero anode by way of a conductance 98 of magnitude delay to the highest conductance. No other equal to the magnitude of the smallest conduct change is necessary, and the operation is other- ance 96g. The output of the triode 91 is sampled wise just as described above. at the pulse group rate by a sampler 99 which may 45 What is claimed is: be supplied with control pulses derived from the 1. In a pulse code communication system, incoming pulse sequence by a differentiator 54, a means for translating signal samples into ni rectifier 55, a band-pass filter 56, a pulse shaper :fiected binary code groups of on-or-off pulses, 51, a 7 to 1 frequency divider, such as a step-down means for transmitting pulse groups to a. receiver multi-vibrator 58 and a pulse shaper 59 connected 50 station, means at said receiver station for con in tandem in the manner explained above in con verting each received group of said pulses into a nection with Fig. 3. conventional binary code pulse group, and means The sampled output is in turn rectified by a for translating said conventional binary code rectifier 1DO and applied in the form of message pulse groups into message signal samples. samples to a reproducer I 0 I. 55 2. Receiver apparatus for translating an in- The operation of this translating circuit is as coming sequence of code pulse groups in each of follows: Pulses of the form D are applied to all which pulses are arranged in accordance with of the delay devices 95a, 95b, etc. in parallel. The the reflected binary code, which comprises means delays of these devices differ from each other by for projecting a cathode beam, a collector for precisely a single pulse period. Thus at their 60 electrons of the beam, a mask having a plurality output terminals all the pulses of a single pulse of similar apertures in the path of the beam, non group occur in time coincidence. Because of the apertured portions of the mask between the aper alternate reversal of polarity of the pulses of the tures being of dimensions equal to the dimensions wave D some of them are positive and others of the apertures, bias means for adjusting the un- negativ~ as required by the Formulae 4. The var 65 deflected position of the beam to a non-aper ious resistors 96a, 9Gb, etc. now effectively multiply tured portion of the mask beyond the first aper the magnitudes of these various pulses by num ture, means for deflecting the beam along the bers of the series 1, 3, 7, 15, 31, 63 and 127, as in mask in steps equal to one half the aperture pitch dicated by the Formulae 4, without altering the under control of suceessive pulses of one incom- fact that alternate pulses are negative in sign. 70 ing reflected binary code pulse group, means for The outputs of these resistors are now effectively restoring the beam to its undeflected position at added by the voltage feedback amplifier 97, again the conclusion of each pulse group, connections as required by Formulae 4. In view of the alter for withdrawing from the collector a current due nating signs of the pulses of the wave D, this to passage of the beam through the apertures of 1J.ddition is algebraic, Therefore, the results. of 715 the mask, wl.J,ich current is a sequence of pulses 2;682,088 15 16 arranged in the conventional binary code, and signal of another magnitude on the application means for translating said conventional binary to it of even numbered pulses, producing a posi code pulse groups into message signal samples. tive pulse for each change of said intermediate 3. Receiver apparatus for translating an in signal in one direction and a negative pulse coming sequence of code pulse groups in each of 5 for each change of said intermediate signal which pulses are arranged in accordance with in the other direction, relatively delaying the the reflected binary code, which comprises means various pulses of a group bY times related to for reversing alternate ones of the pulses of said the several pulse positions of a code group, sequence to form a derived pulse sequence, a whereby said pulses are brought into time coin- plurality of delay devices having delay times re 10 cidence, selectively amplifying the variously de lated to the several pulse positions of a code layed pulses in proportion to the numbers 1, 3, group, connections for applying pulses of the 7, 15, 31, 63, 127 ... 2"-1, where n is the num derived sequence to said delay devices, whereby ber of code digits, adding the resulting amplified they are brought into time coincidence, means pulses, sampling the added pulses at instants fol- for selectively amplifying the outputs of said de Hi lowing the completion of each code pulse group, lay devices in proportion to the numbers 1, 3, 7, rectifying the resulting samples, and reproducing 15, 31, 63, 127 ... 2n-1, where n is the number the succession of rectified samples as a message. of code. digits, means for adding the resulting· 7. Apparatus for transla.ting each of a succes amplified pulses, means for sampling the added sion of signal amplitude samples into a reflected pulses at instants following the completion of :.::u binary code pulse group, which comprises means each code pulse group, means for rectifying the for projecting a cathode beam, a mask having a resulting samples, a message reproducer, and plurality of ~,.pertures arranged in rows and col means for supplying said rectified samples to said umns in the path of said beam, said apertures reproducer. being so distributed among said rows and col- 4. The method of translating an incoming se 25 umns that each row differs by only one aperture quence of code pulse groups in each of which in one column from each adjacent row, elements pulses are arranged in accordance with the re for deflecting the b:;am to a selected aperture row flected binary code, which comprises reversing under control of a signal sample to be coded, and alternate ones of the pulses of said sequence to means for deriving pulses from passage of the form a derived pulse sequence, relatively delay 30 beam electrons through the several apertures of ing the pulses of the derived sequence by times the selected row. related to the several pulse positions of a code 8. Apparatus for translating each of a succes group whereby said pulses are brought into time sion of signal amplitude samples into a reflected coincidence, selectively amplifying the pulses binary code pulse group which comprises means thus delayed in proportion to the numbers 1, 3, 35 for projecting a cathode beam, a mask having a 7, 15, 31, 63, 127 ... 2"-1, where n is the num plurality of rows of apertures in the path of said ber of code digits, adding the resulting ampli beam, elements for deflecting the beam to a. se fied pulses, sampling the added. pulses at in lected aperture row under control of a signal stants following the completion of each code sample to be coded, and means for deriving cur- pulse group, rectifying the resulting samples, and 40 rent pulses from passage of the beam electrons reproducing the succession of rectified samples through the several apertures of the selected as a message. row, the apertures of said mask being arranged 5. Receiver apparatus for translating an in in a plurality n of columns and a plurality 2" coming sequence of code pulse groups in each of rows, where n is the number of digits in the of which pulses are arranged in accordance with 45 code, columns which are adjacent as measured the reflected binary code, which comprises a cir from one side of the mask having successively cuit arrangement adapted to deliver an inter greater digital significance, the apertures of each mediate signal of one magnitude upon. the appli column being spaced apart along the column by cation to it of odd numbered pulses and a. signal distances equal to their widths in the same di- of another magnitude on the application to it 50 rection, the apertures of each column except the of even numbered pulses, means for producing a column of greatest digital significance being twice positive pulse for each change of said interme as high, measured along the column, as the aper diate signal in one direction and a negative pulse tures of the. adjacent column of lower digital sig for each change of said output signal in the. other nificance and being centrally located adjacent direction, a plurality of delay devices having 55 the two ends of the apertures of the adjacent col delay times related to the several pulse positions umn of next higher digital significance, the re of a code group, connections for applying pulses sulting array of apertures, apart from the single of the. last-named pulse sequence to said delay aperture of the column of greatest digital sig devices whereby said pulses are brought into nificance, being symmetrical. about a transverse time coincidence, means for selectively amplify 60 center line parallel with the rows, the single aper ing the outputs of said delay devices in. propor ture of the column of greatest digital significance tion to the numbers 1, 3, 7, 15, 31, 63, 127 ... filling that llalf of said column which lies to one 2n-1, where n is the number of code digits, means side of said c12nter line. for adding the resulting amplified pulses, means 9. Apparatus for translating each of a succes- for sampling the added pulses at instants follow 65 sian of signal amplitude samples into a reflected ing the completion of each code pulse group, binary code pulse group which comprises means means for rectifying the resulting samples, a for projecting a cathode beam, a mask having a message reproducer, and means for supplying plurality of rows of apertures in the path of said said rectified samples to said reproducer. beam, elements for deflecting the beam to a se- 6. The method of translating an incoming se 70 lected aperture row under control of a signal sam quence of code pulse groups in each of which ple to be coded, and means for deriving current pulses are arranged in accordance with the re pulses from passage of the beam electrons flected binary code, which comprises producing through the. several. apertures of the selected row, an intermediate signal of one magnitude upon the apertures of said mask being arranged in a the. application of odd numbered pulses and a 71 plurality. n of columns and a plurality 2n of rows, 2,682,068 17 18 where n is the number of digits in the code, each number of the digit with which the pulse position column corresponding to a particular digit of the occupied by said "on"-pulse is correlated and s code, the aperture pattern being such that, with is the number of "on"-pulses in said code pulse the exception of the two columns of first and sec group having digit numbers greater than d, the ond digital significance, the apertures of each ;; code value of each "off"-pulse being zero, the code column are spaced apart along the column by dis value of each entire pulse group being the sum of tances equal to their heights in the same direc the individual code values of the several pulses tion, and are twice as high, measured along ~he of said group, and means for decoding each group column, as the apertures of that column wh1ch of said pulses into a message signal amplitude. corresponds to the digit of next lower signifi- 10 14. Apparatus as defined in claim 13 wherein cance, and are centrally juxtaposed with the two the decoding means comprises means for invert ends of the apertures of that column which cor ing the polarity of alternate "on"-pulses of each responds to the digit of the next higher signifi received group of pulses arranged in accordance cance the columns of first and second digital sig with said code, means for weighting the individ nificaiJ.Ce each containing a single aperture, the 1 ,3 ual on-or-off pulses of said group in the ratios resulting array of apertures, apart from the sin- 2n-1, ... 7, 3, 1, means for adding the pulses so gle aperture of the column of first digital signifi weighted to provide sums, a reproducer, and cance, being symmetrical about a transverse cen means for applying the sums to the reproducer. ter line parallel with the rows, the single aper 15. The method of translating an incoming se ture of the column of first digital significance fill- 20 quence of code pulse groups in each of which ing that half of said column which lies to one pulses are arranged in accordance with the re side of said center line. flected binary code, which comprises reversing 10. In a pulse code communication system, alternate ones of the pulses of said sequence to means for translating successive amplitudes of form a derived pulse sequence, selectively ampli a message into binary code groups of on-or-off 25 fying the pulses of said derived sequence in pro pulses including means whereby the characteris portion to the numbers 1, 3, 7, 15, 31, 63, tics of said code groups are such that each per 127 ... 2n-1, where n is the number of code missible pulse position in a code pulse group is digits, adding the resulting amplified pulses, uniquely correlated with a particular digit of the sampling the added pulses at instants following code the code value of each "on"-pulse being pro- 30 the completion of each code pulse group, recti portlonal to (-1)•(2