US2438928A - Cathode-ray tube pulse demodulator system - Google Patents

Description

5 Sheet-s-Sheet 1 pms:

Aon/575k E. LABIN ETAL CATHODE RAY TUBE PULSE DEMODULATOR SYSTEM Filed Nov. 13, 1944 Mr/7:5 oF//AcfML-wr EX 2,438,923 CROSS REFERENCE r www M TM. E

a r www. A mwa/W7 2&35928 nn m 19g/ma CROSS REFERENCE SEARCH ROM April 5, 1943- E. LABIN ETA. 2,438,928

CATHODE RAY TUBE PULSE DEMODULATOR SYSTEM Filed Nov. 13, 144 s sheets-sheet z /439 46 50 48 4; i z 1H s VV ./121 125 /zzc /131748a H1 /a EN@ 1FL l 1 f JI 47 [Y [Y /'52 INVENTORS ATTPNFY April 6, 1948.

CROSS REFERENCE E. LABIN ETAL Filed Nov. 13, 1944 SEARCH ROON CATHODE RAY TUBE PULSE DEIIODULATOR SYSTEM 3 Sheets-Sheet 3 65A .aire/ az/972' 65 Maf 7 j .9 6.4/'0/ --lfA INVENTORS Rif/547%@ Patented Apr. 6, 1948 CATHODE-RAY TUBE PULSE DEMODULA- TOR SYSTEM Emile Labn, New York, and Donald D. Grieg,

Forest Hills, N. Y., assignors to Federal Telephone and Radio Corporation, New York, N. Y., a corporation of Delaware A Application November 13, 1944, Serial No. 563,152

(Cl. Z50-27) 15 calms. 1

This invention relates to radio receivers and more particularly to a demodulator for time modulated pulses. l

One of the objects of the invention is to provide an improved-method and means for translating time modulation of pulses into amplitude modulated energy.

Another object of the invention is to provide a method'and means for controlling a beam of energy such as a beam of electrons or an electromagnetic beam relative to a beam sensitive device for translation of various forms of time modulation of pulses into amplitude modulated energy. r

One of the features of the invention is the employment of. a cathode ray tube or other electron beam producing apparatus together with means for controlling the beam and/or the sensitivity 'of a. beam responsive device for translation of the time modulation of the pulses into amplitude modulated energy. The electron beam is caused to sweep through a normal cycle in synchronism with the average timing of the pulses, as when the pulses are free of modulating energy. The beam in its movement is caused to either traverse a. beam sensitive device or to move along a path adjacent thereto. The time modulated pulse energy may be used to control coaction between the beam and the responsive device in any one of several ways. This coaction between the beam and the responsive device causes a flow ofv energy in'a circuit associated with the device, the amplitude of such energy being proportional to the time modulation of the pulses.

One method of controlling the coaction between the beam and the responsive device is to key the beam on and of! according to the leading and trailing edges of the pulses. When this method is applied, the beam is normally caused to traverse the responsive device during a given part of its cyclic movement, whereby the keying on and oir of the beam in relation to such apart, controls the coaction referred to.

Another method of control is to deflect the beam according to the pulse energy. According to this method the beam movement is adjusted so that the beam path is normally adjacent the responsive device, and when the beam is deflected, it is caused to coincide with the responsive device for a. time interval proportional to the degree of time modulation of the pulses.

A third method of control is to apply the pulse energy to an element of the beam responsive device whereby the beam responsive device is made responsive to the beam only when pulse energy is applied to such element. In this method of control the beam intensity is maintained constant, and its path of movement is caused to co-j incide periodically with the responsive device.

The above and other objects and features of the invention will become more apparent upon reading the following detailed description with reference to the accompanying drawings in which:

Fig. 1 is a. schematic block and wiring diagram of a receiver according to the principles of this invention:

Figs. 2. 3 and 4 are graphical illustrations useful in explaining the invention;

Figs. 5 and 6 are fragmentary illustrations of variations of the energy collector means shown in Fig. 1; and

Fig. '7 is a schematic block and wiring diagram of a further variation of the invention.

Referring to Fig. 1, there is shown a radio frequency `receiver l with an antenna 2 for receiving pulsed radio frequency energy. the radio frequency carrier being removed .by the usual detector means thereof. The pulse energy thus detected may be modulated according to any one of several principles of time modulation. For

"example, the successive pulses may be time displaced toward and away from each other according to the push-pull type of time modulation or the pulses may be modulated in width, either symmetrically or by displacements only of one edge thereof, or the successive pulses may be time displaced relative to their unmodulated time positions. These are the more common types of time modulation but it will be clear as the description proceeds that practically any type of time modulation of pulse energy may be demodulated, that is, translated into amplitude modulated energy, according to the principles of our invention.

The demodulator part of the system shown in Fig. 1, comprises a cathode ray tube 3 having the usual electron gun equipment 4 for producing a beam of electrons which is controlled by grid 5 and shaped by the usual focusing means 6. The beam is projected between two pairs of deflection plates, 1, and 9, Il). 'I'he deflecting voltage applied to the plates l, 8 control the normal sweep of the beam on the screen il with respect to a beam responsive device or collector I2 which may be disposed on one face or the other of the screen Il, depending upon the characteristics of the screen and the collector. The deilecting voltage applied to plates 1, 8 is produced 3 .by a wave producer I3. The producer I3 may be synchronized with the detected pulses through known synchronizing means I4. Should the wave energy desired be sinusoidal, producer I3 might include a tunable shock excitable capaci- -tance-inductance circuit, or if the wave desired is o! a saw-tooth character, theproducer might include Va known Vrelaxation oscilla-tor adapted t-o be controlled by the detected pulses. In either case, the wave generated should have recurring substantially inclined portionsandhavearperiod comparable in at least a harmonic relation-.to the average timing of the pulses. Eor controlling the phase relation ofthe .wavenaphase ad- `luster l5 is included se that the sweep cyclefof the beam with respect to the collector I2 and the' average pulse timing will produce the desired current condition in the output-circuit ftfoffthe collector I2. The current flow produced inthe circuit I6 may be applied to a low pass filter I1 Aand thence to a utilization circuit such as phiinesd.

The circuit o1' Fig. 1 -is 4arranged `to provide -a selection with'respect -to the 'control ofthe -cathoderayjbeam :byl the detected pulses from -receiver 'rangement I9 whereby a-movablecontact 2li-con- Ttrnls the application oi the input pulses tcreither thegrid'i or over circuit :2l-to deectiomplates 9, I0. As shown. the-contact 2D is positioned to apply the p ulses to the grid 5 whereby the lbeam jls'lkeyed on and oil according to 'the occurrence of the Aleading and trailing edges of each pulse. The grid 5, lfor this position of the movable-contacts Aof switch 19, lsiprovlded with a'highnegav tive bias bybeing -connected over Vcontact-"22 to 'the negative side -of a source ofi-potential -HC -whose positive side is connected'to 'the -cathode via ground, whereby the grid is normallysbiased to cut or! in the absence of pulse energy. The.

bias voltage of the grid is controlledby rcontact '22. iMovable contact-'23 provides a Yground for the P19594 when the switch'is 'inthe `position illustrated in'lig. 1. 'When the contacts Aor switch 1 3 .aremoved to thepositlon opposite that shown, 'the contact 23 is moved free of ground connection 1l, the contact-22 is 4moved 'to a low sourceof 'biasing potential LC whose positive side is connectedzto ground, and contact is movedto close'connection with line 2| to plate 9. The'low 'bias'lfC provided for the grid '5 in this position ai' switch t9 insures a now ofelectrons'to'iorm a .beam o! constant intensity. Uther biasing circuitsor the circuit of Fig. 1 will be apparent to those versed 'in the art and. accordingly the details thereof .are omitted.

'For the purpose of explaining the operation `of the system of'-F ig.`1, whentime modulated pulses are applied to grids. the .graphs of'Fig.' 2 are' provided. Graph a'illustrates a train of .pulses 25 which is ltime modulated according tn jthe pushfpullprinciple. It will be noted alsothatthe pulses 'have a given oiset bias. that is to say. theypulses. in the absence o! modulation. 4will assume a paired ont spaced relationship. Graph 'li-,illustrates a sinusoidal wave 2B such as maybe produced at wave producer 'I3 'in accordance with the average ltimingi the detected pulses. Graph c 'representsthe coincident vtiming ,oflthe collector 12 at 't2a,"l2b, etc., with respect to a given portion of the cyclical movement of the wave 26 and also the pulse occurrence .timing -as represented by the 'keying on and .off of the beam .at 2Ba,18a,f30a and ila. Graph d represents .at fthe pulse `energy owingin Athe yo utxuit circuit x ,sw y

5 time displacement, pulse 29 is shown displaced to the right about 50%, Pulse 30 is shown to be cen- .tered at .zero modulation and pulse 3| is shown displaced about 50% tothe left. The displace- .ment of pulse 28 is shown to key the beam on loor complete coincidence with the collector I 2.

'dihecoincidenceof-the keyed-on beam with the lxxdllector at I 2b is shown to have only about coincidence .with.the.collecto while the centered vpulse:liliashovvn to provide a 50% coincidence .15;.and- .the pulseglluto provide about 25% coinci- .fdencesvith thecollector I2. The current flow in circuit I6 being proportional to the number of electrons impinging upon collector I2 during each keyed-:on part of the beam cycle, produces an out- 20 put pulse. as indicated by pulses 27 for the time positions of pulses 25.

Assume -now that the switch I9 is shifted to -the right so as toprovide a. low biasy LC on grid 5, to apply pulses from receiver I to denection 25 plates'e, -I0 vandto vremove the ground connection ..I. This selection -is controlled -by 'af switch ar 2t from line `2I. -InV this condition it will be assumed'that-the contact 23 'now applies -a. constant voltage from battery 32 te the Vplate 9 in addition to-the energy of the pulses from receiver I. This,as indicatedin graph 'a of Fig. 3, causes lthebeam 'to sweep Aadjacent the collector I2, as `indicated at' 33.

"For the purpose orillustrating afurther form 'or time-modulation. the-pulse train 34 of graph e 35 is shown to be modulated in width.. For example,

fthe successive pulses 35, 36, 31 and A'38 are pro- -gressively greater in width. The'wave producer I3 may provide either a. sinusoidal or saw-tooth `wave-substa-rxtiallyes indicated at 39 and 40 in 40 graph J'lfor" application to the deflection plates '1 andf. "The-pulse 36 represents the pulse width -in--'the'absence of a modulating signal. `When this pulse energy -is applied to the deiiection plates 9 and 10, the beam, which now is keyed on constantly at -a given intensity is deflected for interception with the collector as indicated at 42h. The output energy of the collector circuit fi :is indicated at 4I, graph h, which vis of ampli- "tude' proportional to Athe electrons collected by .50 the-deflection produced in response to pulse 36.

'Pulse S5 :is shown to be of a smaller width and maytherefore be regarded as representing a modulating signal of negative potential. The denection ofthe beam in response to this Apulse produces a coincidence with the collector I2a for a duration corresponding to .the pulse width, the output .pulse lthereoi being represented at .42. Iikewise thegreater .widths o1' .pulses 31 and 38 AProduce =upon .delection oi the .beam pulses .of

.60 greater amplitudeasindicatedat 43 and .44.

Graph iol. Fig. 4 shows va further principle of time modulation` wherein the lpulsesare time displaced .relativeto theirnormal timing according to the instantaneous yalue .of the vmodulating .6 5 signal. l These pulsesareapplied.tothedeectng plates 3 and I0 .similarly as described .in.connec tiqnwith the .pulsetrain .34 .of Eig. 3. .Graph y' represents .the deflection of the beam during its trace 33 with respect to the collector l2, .thus

.10 indicating the degrees oi coincidence of the de ilected lportions therewith. Pulse 461s shown to be -in an unmodulated .position and -according .no .graph j producesa.50% coincidence between the .beam and ,the ,collector `I2b, as indicated at .25 .46a, ,.thereby.fproducinc .anaverage now of cur- .5 rent las .indicated rat A1. The 'pulse-48, fhowever. is .shown to beinahe extreme-position-offmodu- ,lation and in suchposition; the deflection at '48a is shown .to be displaced to one side of :the fcollector I2d. Thus, the rcircuit yIB doesfnoteonduct currentfor the pulses'in thisextremeposition. Pulsesl and Ellware vshownto bedis placed a given distance inppposite directions from 'the Centered -position` ofpulse l.46, and they produce. according. totheresulting degree of coincidence -of the beam vand collector I2 output pulses 5I .and 52,A respectively.

In Fig. 5 .a-collector arrangement :is shown wherein the screen I I includes a liuoresoent coating'53. The outer main .portion of -thescreen is coated .with an opaque substance zasindicated at 54, vleaving a smallopening .at'55 over-which-a selenium. type .of photocell 551s positioned. .Atype of a cell other than selenium may.of course-be lused. This selenium cell isresponsive to the light .produced by the .beam on the-uorescentfsub- .stance 53 so thatfw-hen the beam-is keyedon or deflected for coincidence with the fluorescent screen area of aperture 55, .the cell responds to produce aliiow of current in output circuit-Ail, the

amplitudeof .which corresponds to the'degree of coincidence of the beam with respect to the aperture area. When the selenium cell is used it-may be desirable toadd .ampliers to circuit I6 to boost the amplitude -of the outputpulses.

In Eig. 6V a variation of the plrotoelectric cell is shown utilizing the. ordinary gas or Iphotocell las indicated at 58. Disposed in spaced relation .in front of-the-.ucrescent coated screen I'I is a barrier'plate 59 .havingan aperture 60 in alignment with the cell 58 and a lens 6I, whereby an area 62 of the fluorescent screen is lfocused upon the cell 58. The. cell 53 thus-responds-to thecoincidence .of the beam with the area GZto producepulse energy as hereinbefore described in connection with Figs. 2, -3 and 4.

In'Flg. 'I a cathode rayitube163 is shown similar in construction to the tube .31ct Fig. 1, exceptthat the collector arrangement is of the secondary emission type. rI'Ihe collector, or rather, beam sensitive equipment of this tube, includes a dynode 64 which is located in spaced relation to a barrier plate 65. The barrier plate has an aperture 66 in alignment with the dynode $4 whereby the beam when in coincidence with the aperture 66 impinges upon the dynode 64, thereby causing secondary emission of electrodes from dynode 6d to the barrier plate G5. In order to provide this condition the barrier plate 65 is maintained at a high potential HB while the dynode 64 is maintained at a lower potential LB as indicated by connection 61, movable contact 68 and bias source 69. In the positions shown in Fig. 'I for contact 2U, 68, l0 and 1I, the pulse energy from receiver I is applied together with cut-off bias HC from source 'I2 to the grid 5 the positive side oi' said source being connected to the cathode via ground. The bias HC maintains the grid at cut-ofifso that only the pulse energy applied thereto keys the 'beam on and ol similarly as hereinbefore described in connection with Fig. 1. The operation of the tube 63 is substantially the same as described in connection with tube 3 of Fig'. 1 except that the secondary emission feature of this tube provides a much greater signal amplitude output than is obtainable, for example, by collector I'2 of Fig. l or the selenium cell of Fig. 5. The dynode arrangement has a further advantage in that a fluorescent screen is not used thereby avoiding halatlon defects that occur O I O ,casacca infthe fluorescent coating and .glass of screen I- I,

and in addition allows the return current;to.:.ow through the Vdynode-anode circuit rather than through thebeaxn1 therebyravoiding: spaceecharge eifectsras-well:asthejhighrimpedance-effectof the beam.

-.Besides, the-keyed on-and oicontrol: ofzthegrid 5,-1the deflection of :thevbeam may be --controlled by the pulses over connection .2i toplatesaB, I0 byswitchingcontactslli and 23- to` theright similarlyfasfdescribedin 'connection with the circuit of;Fig. l. ifilhen-.thisrhangeis made it lwillralso Abe desirable-to shift thescontacts y'It and 1I to .the left so asto provide a cut-oft bias from source .13 :to A grid f5. In ltbis condition f the Voperation is substantially :the samei ashereinbefore described in connectionwith Figs. 3 and4, .with theexception :that the. output Acurrent is .here .produced by secondary emissionfbetween elements .6'4 and 65.

AInaddition to theseitwo beam control operations, the coactive relationship betweenthe beam andthe dynode maybe oontrolleciby varying the sensitivity-of .the dynode in accordance withthe pulse energy. 'This isaccomplished 'oy placing in Fig. 7 all of thecontacts 20, 23, B8, To and-1I to the left. In tlnscondition, the pulses ffrom receiver I are applied through contacts 26 and lil and over connection-51 to the dynode 54. 'In addition, the dyncde 64 is provided with aout-off bias from source i4 thrcugh-contact'li-.- Thus,

lthe dynode in the absenceof -pulses will not respond to the electron-beam, but'when'biased accoi-ding to the energy ci' the time modulated pulses will respond according to the degree of coactive coincidence of the beam therewith, thereby l producing a. corresponding pulse ainplitude output. (In this case it may be necessary to reverse thepolarity of the pulses from. the preceding in ordertotcause the dynodepotential to drop.v during the. arrival ofv .eacl1.pu.lse.)

WhileA we have .disclosed the principles ofcur invention in'connection with specic apparatus, it will be clearly understood that such apparatus is given by way of illustration only and not in restriction of the scope of the invention as set forth in the objects and the appended claims.

We claim:

l. A demodulator for time modulated pulses comprising means -or producing a beam of energy, means for causing said beam to sweep through a cyclic movement in synchronism with the timing of said pulses in the absence of modulation, whereby coincidence of said pulses and a given part of said beam movement is varied in proportion to the amount of time modulation of said pulses, and means for causing a iiow of electrical energy proportional in amplitude to the degree of coincidence of said pulses and said given part of the cyclic movement of said beam.

2. A demodulator according to claim 1, wherein the means for causing flow of energy includes means for keying the beam on and off according to the leading and trailing edges of each pulse.

3. A demodulator according to claim 1, wherein the means for causing now of energy includes means for deflecting the beam from its normal movement with respect to said given part of its cyclic movement according to the energy of said pulses.

4. A demodulator according to claim l, wherein the means for causing iiow oi' energy includes means responsive to. energy of said beam and means for controlling ,the responsiveness 0f said 7 responsive means according to the energy of said pulses.

5. A demodulator according to claim 1, wherein the means for causing the beam to have a cyclic sweep movement includes means for producing a voltage in response to the time modulated pulses which is of substantially constant cyclic pattern, and means for deflecting said beam according to said voltage. 1

6. A demodulator for time modulated pulses comprisng means for producing a beam of energy, a beam sensitive device, means for causing said beam to sweep through a cyclic movement, the path of which bears a given relationship with respect to the location of said device, means for causing said beam to coincide with said device in response to at least certain of said pulses, and a circuit associated with said device for conducting a iiow of current in response to coincidence of said beam and said device. l

'1. A demodulator according to claim 6, wherein said beamis an electronic beam, and said device includes an electron responsive element.

8. A demodulator according to claim 6, wherein said device includes means for producing light upon coincidence with said -beam and means re-l sponsive to intensity of said light to produce ilow of current.

9. A demodulator according to claim 6, wherein said device includes .a nuorescent screen responsive to said beam for producing light. a light responsive cell associated with said screen and means for defining the active area of said screen with respect to said cell.

10. A demodulator a'ccording to claim 6, .wherein said device includes a barrier disposed in the path of said beam, said barrier having an aperture therein, a dynode disposed in alignment with said aperture for interception of said beam when said beam is projected through said aperture.

11. A demodulator for time modulated pulses comprising means for producing a cathode ray beam, means for producing a sweep voltage for controlling the cyclic movement of said beam to pulses.

cause said beam to follow a given path, means for synchronizing said sweep voltage with the timing of said pulses in the absence o! modulation, a beam responsive device for producing a current when said beam coincides with said device, and means to cause said beam to coincide with said device in accordance with the time characteristics of at least certain of said pulses.

12. A demodulator according to claim 11, wherein said device includes a barrier member having an aperture for passage of said beam, and a dynode element disposed in alignment with said aperture for interception of the beam passing therethrough.

13. A demodulator according to claim 11, wherein the means for controlling said beam in accordance with said pulses includes means for keying the beam on and on according to the leading and trailing edges of each pulse.

14. A demodulator according to claim 11, wherein the means for controlling said beam in accordance with said pulses includes means for deecting the beam from its normal path of movement in response to the energy of said pulses,

mE LABIN.' DONALD D. GRIEG.

REFERENCES CITED The followingv references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,344,745 Somers Mar. 21, 1944

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