US2401010A - Television signal generator - Google Patents

Description

May 28, 1946. F, MAYLE 2,401,010 TELEvisIoN SIGNAL GENERATOR; Filed Jan. 10, 1944 2 sheets-snee 2 LQUI'SF. MAYLE nent of the video signal. two components is afluctuating voltage which,

at any instant, is related in value to somefl'xeda. reference voltage incorrespondence withth'eab:

solute brightness of the elemental picturearea' Paten u 8;. 4 a

,- TELEVISFON SIGNAL Qumr n Mayle, Fort Wayne, Ind assignor-to e .Farnsworthjlelevision and Radio (lorporation,

"a corporation of" Delaware Application January 1o, 1944,'sei-ia natiasis goi imsf (c1, its-7.2) 1

This invention relates to television systems and V essary in: prior uses of, image analyzing. tubes of Y particularl to the nals. I

In the operation of television systems it isnecessary to impress signals upon the reproducing device containing all of the information necesgeneration of "television sigsary to reconstitute the picture substantially in its original form; Oneitem of information comthe'iconoscopertype to employ auxiliaryapparawe to provide a voltage representativebflthe mean picture brightness to which maybe re- .ferred the values ofthe fiuctuating voltage obtained from a tube of this character in order to produce avi deo signal suitable to reproduce sat- .isfactorily the television subject.

prises the light andshade variations existing between the elemental areas of thetelevision subject. Of substantially equal importance is information regarding the average" subject illumination or mean picture brightness. The former ordinarily is represented by a voltage fluctuating relatively rapidly I from one value to another. This is the so-called A. 0. component of the video signal. The latter ordinarily is represented by a voltage varying relatively slowly from one value to another. This is-known'as the D. C. compo The combination of being scanned.

It is .well known in the art that,.wherea conventionally operated iconoscope is used as an image analyzing device in a television signal generator, it is possible to obtain from' the output circuit of the iconoscope onlythe so-called-A. C. component of the video signal. 'I'hereason for thisisthatthe iconoscope is 'essentially an alternating current device. As such, there is" available only one reference voltage and that is the avera e value of the relativel rapidly iiuctuah ing voltage representing light-and shade values of the subject. Since these voltage fluctuations do not occur according to any fixed periodicity,

. the average thereof rarely issymmetrically disposed with'respectto the maximum and minimum peaks. of the fluctuating voltage." Instead. it is displaced from such a position of symmetry in the" direction of the predominant fluctuating voltage value. Theresultis'that, with respect. to the average value of the fluctuating voltage.

thevalue of thevoltage representing an elemen tal picture area of given illumination varies in accordance with the mean picture brightness.

Thus, the requirement that'the fluctuating voltage bear a relationship to a fixed reference voltage in correspondence with. the absolute'brightness of the elemental picture area is notmet. Consequently, a signal voltage of this character is unsuitable for'use to reproduce accurately a television subject. It, therefore, has been nec- It is an object fthe present inventionijtherefore, to provide a television signal generator .employing an image analyzing tube such as Tone of the iconoscope type whereby the signal derived from the tube contains both the videoinformation and the average illumination information; Another object of the invention is toprovide a novel method of generating fa television fsignal whereby to derive a television signal comprising both video and average iluminationinformation from an t ne image analyaingtub of the iconoscope In accordance the instantin ventiontliere fis provided an image analyzing tube suchjas a f-conventionaliconoscope having a mosaicand means for producing an electron beam by means of which to scan themosaicwhich isanodically related to the beam producing means. The intensity of the scanning beam is modulated at'a carrier frequency during ,trace intervals. a

consequence there'is derived fromthe output cir cuit'otthe iconoscope carrier frequency energy which is modulatedin amplitude in accordance with the light and shade values of elemental areas of a television subject. The carrier. frequency energy'also includes the so-called D. C. component .whichds the information regarding the average intensity of thesubject illumination.

The derived'carrier frequency energyis modulatedonly to a relatively small percentage; Ac-

cordingly, a multistage videoqamplifier is provided to amplify the derived carrier H frequency energy suiiiciently to produce a peak to-peak voltage of "themodulated portion of s'uflicient magnitude to render it 'useful' for transmission purposes. In one "of thejhigher video amplifier stagesthe amplified carrier frequency energy is l subjected to fa limiting or clippingaction whereby to'elimin ate the unmodulatedportion of the energy leaving only the modulated portion for subsequent impression upon the transmitting apparatus. I During retrace intervals of thescanning beam the carrier frequency intensity modulationtherm of is interrupted by means controlled'by "a timing device, therebyreducing the output voltage of the tube substantially to zero. In order not on the interior or the tube envelope which ex thereof.

- frequency.

- to produce a discontinuity in the carrier-wave reference is bad to the following description, 1 7 taken in connection the accompanying :draw- 2 ings and its scope will be pointed out'in the appended claims.

In the accompanying drawings: Fig. 1 is a schematic circuit diagram. partly diagrammatic, illustrating a preferred embodiment of the invention; and,

son' with conventionally operated apparatus.

iReier'r-ing now particularly to Fig; 1, there are shown those components of a television itransmitapparatus necessary for a complete understanding of the'invention. "I heimage'mnaflyz'ing tube 3 may be a conventional "iconoscope having a mosaic I2 and associated metallic "plate 3.

{The ioonoscope also provided with the collectoriano'de 4 in the form of a wan coating tends down into the neck :of the tube..' The electron beam for (scanning the mosaic is developed and controlled by electron gun apparatus located 1 in thefneck of the'tube. "This apparatus comprises an electron mitting cathode 5, an intensity control electrode 5,12. focusing electrode I and a ventional and has not been shown iorthe reason that it forms no part of the present invention and is considered unnecessary {to an understandin The light which is reflected from a television subject "9 is focused ontothe mosaic 2 by means of a suitable optical system diagrarnmatically .rep-' resented herein by the lens 11.

The output circuit electrodes of theicono'scope,

comprising the signal plate 3 and the collector anode l, are connectedjrespectively to the terminals of :a tuned circuit 12. The tuned circuit .in-

eludes an inductor 13 connected in parallel with the interelectrode capacitance between the signal plate and thejcollector anode which is represent-- ed by the condenser 14. circuit'is tuned sharply for resonance at a predetermined. carrier "The signal developed in the tuned circuit 1 z is impressed upon a utilization circuit including .a. .miutistage video amplifier. In the presentembod'iment of the invention this amplifier comprises stages, each of which includes a'multielectrode vacuum tube. The tubes for the .suc-

' cessive stages :ofthe video amplifier are is, 1'6,"

ll, 18 and 19, respectively, and may be of the V 6AK5 type or its equivalent. Associated with the output circuits of each of the amplifier tubes to in inclusive are tuned circuits 2|, 2'! and 23,

respectively. The circuit M comprises theparallel' connection of an inductor 24 and the interelectrode capacitance between the anode and the screen grid 25 of the tube 15 and represented by 1 Figs. 2 to 7 inclusive :are graphical representaitions illustratingjthe operating characteristics of apparatus embodying the invention in compari- 'unidirection biasing energy suchas the battery 4.0. second anode 3. The scanning apparatus for de-,,. 7 :fiecting the beam over the :mosaic may be conthe condenser-*3. The circuit 22 comprises the parallel connection or :an inductor 21 and the interelectrode oapacitance between the anode and screen grid 18 of the tube l6 and represented by the condenser. 29. Similarly, the tuned circuit 23 comprises the parallel connection of an inductor 31 and the interelectrode capacitance between the anode and-screen grid 32 of the tube l1 and represented bythe condenser 33.

' Th iciroui'ts '21 and 2 3 are tuned sharply for 'resonance'atQ-"a frequency which is a predeterv mined amount higher than the carrier frequency. The circuit22, on the'other hand, .is sharply tuned .for'resonahce' similarly to the circuit i2 at the carrier frequency. The purpose of this arrangement will fbefrnade clear in a following portion of the specification describing the operation of thesys g -.In the cases of the tubes 15, I5, I1, l8 and IS the respective suppressor grids 34, 35, '36, '31 and 38 are connected directly to their associated -:cathodes. terminals of the tuned circuit l2 are connectedfrespectively to the control grid 39 and the grounded cathode of the first stage am- .pllfier tubejf in series with a suitable source of 41).. One terminal of the tuned circuit 2] and the screen grid of the tube 1 5 are connected to the positive teririinal of a source of unidirectional energy such "ska battery 4.! :of which the negative terminal .i connected to ground. .By means of this connection space current and screen grid po- I 'tentia-l are supplied to the first stage amplifier 'tub 1:5. Thei'other terminal of the tuned circuit 2| is'coupled by nieans oiacondenser 42 to the control grid 43 i of the second stage tube IS. A

leak circuit tor the condenser and a suitable biasing circuit tor the control grid of the tube l6 comprises the connection of a resistor 44 from the control grid through a source of unidirectional biasing energy such as the battery 45 to ground. -Sirnilarlyfdne terminal of'the tuned circuit 22 and the screen grid 28 of the tube 16 are conf nected to the positive terminal ofthe battery 41 in orderto provide space current and screen grid potential forthe tube 15. The other terminal pf thextuned-circuit 22 is coupled by means of a condenser to the control grid 41 of the third stage amplifier-tube H. The leak and biasin -.circuit for tube com rises the series connec- V tionofa resistor 48 and a source of unidirectional 'biasingenergy such as the battery 49 connected between the control grid"v of the tub ll .andgroundf l a V v. e

In'like manner-one terminal of the tuned circuit!!! and the screen grid of the tube H are connected to the positive terminal of the battery 7 M to provide space'ourrent and screen grid potentialfor the third stage amplifier tube H. The other terminal of the tuned circuit-.13 is coupled by means or .acondenser 5| to the control grid 520i the fourth stage amplifier tube l8. A grid leak and biasing circuit for this tube is provided by the series arrangement of a resistor 53 and a a5 source'of unidirectional biasing energy such as v. the battery 54 connected between the control grid .of the tube 18 and ground.- In the case of this amplifier stage the potential of the battery 54 is chosen so as to blas the input circuit of the tube 70 sufllclently negative to effect the operation thereof as a. class C amplifier. The purpose of this arrangement will be made clear in a followin p rtion of the "specification in which the operation-of the system is described.

75. Thescreen grid 55 of'the fourth stage ampli radiated: .wave.

to this electrode. The anode oi-thistubeistcontor 58 to receive energythereirom; The ter'mi- V nalsof the inductor'il are 'vconne'cted totiie terminalsof a voltage developingresistor iBJThe inductors 56 and 51 are mutually arran edi-in a manner to, form a bandpas's-'cou1:il-ing'v circuit;

One limiting frequency of the band is substantiah ly equaltothe *frequencyltowhich the circuits 2| and 23am tuned and the other limitingirequency is substantially equal tovthe frequeney*"towhich thecircuitsiland 22 are tuned. i

tube [9; Thebther terminal "of the resistor is a connected through a source of! unidirectional biasing energy such as the battery tl to ground.

pThiS battery; is shunted by 1 a by-pass condenser 62- forcthe purposeofproviding an alternating currentcircuit to ground for the input circuit resistor 58. v The screen grid ilofirthe tube I9 is connected to the positive terminal of the battery 4| to provide; a suitableoneratingapotential'fcr' this electrode; ThG fihOdQOf this tubeais connected throughan output circuit inductor- 64 to the positive terminal? ofthe battery My; The tube J9 may beat the same typeas the tubes; to l-8;

inc1usive,- if.: desired, "and may be connected as? fier tube i8 is connected to the positive than oscillator 881s connected also inciudesa carrier o: the battery Htoprovlde a suitablep'otentiai wave amplifier fl the output terminal sof which i are connected to an inductor li 'k Thisinductor nected throughaninducto'r 56 to theposltlve terminai of, thebattery 4|. Anotherinductor '51 is cooperatively arrangedwith respect to the inducis cooperatively arrangedtwith respect to the "inductor 51 for the transfer pfijcarrier wave energy to theinput'circuitof thbtube I91] P The carrier wave ampiifiers fi q and ti are controlled' by sign V -synchronizing signal so r e {83, This signal I source isconnected tozthe blasin'g circuitsfof the amplifiers 69 andllfi'n a mamentrender-"theseamplifiers} operatiyefalterhately for afbiirpose to be described ina following portion oi'the specification relatingto the alsz ld'erived from: a {blanking and operation it of ilt ystern.

1 Referring nowto'the operation of thedescribed i 7 1 f apparatus, a sumethatthevariouselectrodes of One terminal of the resistor-His connected to i the controla grld 59: of. the fifthstage amplifier scope I are providedfwith appropriate potentials.

potentiometer-*1!" such th rnie magnitude r the f ntroi. electrode" Wis suitable to compietelyjvinterrupt the how of "v electrons past; the electrode intheabsenceofthejdevel pment of carriefiwave biasing potential impressed upon the intensity F energy in the-.indu'ctorffik The switching arrangement provided for lthefcarrier wave ampli tiers; 69' andv 8! [is 0 f such a character that the amplifier tsj'isonaitionea for o eration andthe described, whereby the suppressor grid "thereof is notutilized; I v. V v

There is inductively coupledtdthe'output insired, or, as shown, directly to a transinitter 66 whereby the modulated carrier wave energy n ay be converted into a'iorxn suitable tolbetrans mitted froma radiator 61; i

; v The transmitter system'al'so 'inciudes-a'source of carrier wave energy such asa local radio'fredenoteany desired frequencysuchas a sub can: rier or intermediate frequencyor even the radie ated frequencw This oscillatords connected to two separate circuits, oneof which includesacarrier wave amplifier 89. The output'terminals of this amplifier are connectedto an inductor. 102;

V doctor 64, another inductor 65 which maybeiconnected to additional amplifying -apparatuszif deamplifier- H isinoperatively conditioned during trace, interval of' the electron beam over the iconoscop'e mosaic Duringiretrace. intervals 'the carrier -waveamr'iliiier 8| is operatively con.

incperatively conditioned. .Thi -anmliflefjswitcm ing isun 'nal source.

ditio'nedand the carrier-{wave d r the control or the synehronizin'g'sig- During trace intervals in the scanning: o tion'the' electron beam is modulated in intensity atthe frequency oi the carrier wave source which maybe of the order of 2b megaoyclesgfionsequentiy, asqthe beamii bombarding each elemental area i of the mosaic 2flit .will' beimfddulated in intensity through a n mpergorcynes 0f the carrier wave. The signal 'voltagewhichis developedi between thesignal lat-eke ndftn collector anode [then is a carrier; wav at the fre- V quency of the radio frequency oscillatoryi g which is modulated inamplitude in" accordance V with ,the electrical condition obtaining at the successive elementaliareasofrthe scanned]mosaic! The exceeds-modulationoi'ithe order M 1096? I with which there 'ls cooperatively: arrangedfor the inductive transferof energy an inductor 1i.

One terminal of this latterxinductor isiconnected to the intensity control electrode 6 nt the electron tioz'neter Tl The resistor "and the potentiometer 13 are shunted bye-albypass condenser 15;:

. gun. The 'other terminal of theind'ucton'll'is 1 The; potentiometer-1'4 isgconnecte'd in seriest with resistors .1 8' and 1-1 ;1- another 'potentior'rieter' "18 and a source of u'nidirectlonal energy such-as the battery 19'. The" positive. terminalor this battery-is connected to ground and the negative terminal to one terminal of the potentiometer 14;

1 The adjustable sliding contact 80 1 or: the potentiometer 18 is connected ito the focusing anode 1 ofthe electron'gun. v 1 my The second circuit to whichthe radio'irequen'cy dept hof modulatioriof the carrier Vwa've may not isomericse this type ofsighal it isnecessary tofincrease'the relative magnitudes orgratio otthe voltage representing picture blackarid that so relativelydow; percentage modulated" carrier wave representing; picturemhite; For this urpose the is" impressedr'successively upon] the a plurality of video amplifier stages .arrangedjin cascade. The multistage video' tu'nplifierv provided herein must be capable of amplifying the modulatedcarrier wave together with a predetermined number of its side band frequenciesproduced by the moduiated video 'sig naL-j' Accordingly; the amplifier. is designed' toj function effectivelygto amplify a predetermined :band or frequencies, including the carrier-wave and the desiredinumber c sideband frequencies a i "'I'1ie .manner.in1which thisis accomplished is Y by means oftli'e tuned circuits in; 22fa d ll.

Inasmuch as the signal voltage "developed" output circuit of theiconoscope is relatively weak.

vides a satisfactory compensationfor the attenu- 23 to the upperlimiting frequency of the. upper V ulated in amplitude'in accordance with the video band frequencies are-amplified by the tube It" 'and coupled to the transmitter 66 for suitable and generally not much in excess of the level of noise. elects. it is desirable to tunethe circuit l2 sharply for resonance at the carrier wave frequency. By this means it is possible to develop a video signal of a character which ha the greatest possible signal-to-noise ratio. However, the

greatly not only against the noise effects but also 1 thevideo signal modulation of the carrier wave. In the present instance it is assumed that it is desired to produce a video signal modulated car'- rier which will include, in addition to the carrier wave frequency, only the upp r s qeizband frequencies. To this end the circuit-"1i is tuned sharply for resonance at that upper side band I frequency which has the greatest deviationfrom the carrier frequency. arrangement pro- 7 ,2 ation of the upper side band frequencies produced by the tuned circuit i2 and theincidental desirable suppression of the lower side band frequencies. In like manner, the tuning ofthe circult '22-to the carrier frequenc'yiand the circuit side band frequencies serve to provide an amplifier having a band-pass characteristic by. means of which the carrier and its upper side band frequencies are amplified. s

- After successive amplifications of the relatively low percentage modulated carrier wave, the voltage difi'erence of the portion representing picture black and the portion representing picture white is increased sufficiently to be usefully employed. However, the larger proportion of the carrier wave energy is unrnciiulated and can not be usefully employed; It is this type of signal which is impressed upon the I input circuit of the amplifier tube '18., The biasing of the input circuit of this tube is of; such a character that the stage operates as a class C amplifier. In other words, it is responsive only to signal voltages exceeding a 'magnitude determined by the negative biasing voltages impressed upon the grid of the tube. In 4 the present instance this signal voltage magnitude issubstantially equal to the smallest value of the modulated portion of the carrier, wave. Thus, there appears in the output-circuit of the, tube i8'an amplified carrier wave which is mod 5 rier wave, together with the desired upper side band frequencies, is coupledby means of the inductors 56 and 51 to the input circuit of the fifth stage amplifier tube 19.- By'rea'son of the band pass character of the coupling inductors 56 and 61 the modulated carrier wave and its upper side conversion and subsequent radiation. v During retrace intervals in the scanning operation the synchronizing signal source develops a signal under the control of the usual tim- 6 ing apparatus at atime coinciding with the funccircuits of the carrier wave amplifiers 69 and 8| in suitablepolarity to render the amplifier 69 inoperative and. the amplifier 8| operative.

The interruption of the supply of carrier wave electron gun the bias voltage impressed upon this electrode by the sliding contact II of the potentiometer 14 to completely interrupt the beam whereby toprevent it from reaching the mosaic 2.

"blanking"-the image analyzing tube. 'As a con- I sequence, the signal voltage derived from the out- This step is commonly known as put circuit electrodes.) and 4 of the iconoscope I is reduced substantially to zero at which value ';facilities for preventing. adiscontinuity of the originating at the source '3 to control the in- Jection offcarrier wave energy at a predetermined amplitude and at the radiatedfrequencyin any one of a number of ways-within the skill of those versed in the art. In the case where the carrier wave energy derived from the output circuit of the iconoscope is at a sub-carrier frequency or an intermediate frequency with respect to the frequency of the radiated carrier wave, the in- Jected energy may be atthe radiated frequency or atthe' subcarrier or intermediate frequency. In accordance with the illustrative embodiment of the invention the injected energy is at the frequency of the local carrier wave source ll.

. black. In such a case a synchronizing signal may be developed by suitably modulating the carrier wave energy supplied by the amplifier Si or in an equivalent manner. For example, in television signalling systems using negative modulation duringtrace periods; the maximum amplitude of the carrier wave represents picture black and the minimum carrier amplitude rep- I carrier wave are.

resents picture white. In'such a case, the synchronizing signals may be produced by increasing the amplitude'modulation of the carrier wave to exceed the amplitude representing picture black. 'However, a far asthe present invention is concerned it is immaterial whether positive or'negative modulation of the carrier wave is employed or what the amplitude relationship of the synchronizing-signals to other portions of the It is considered to be within the skill of those versed in the art to adjust the a circuit components suitably to provide the necesenergy to the intensity control electrode 8 of the 7d sary carrier wave amplitude to the transmitter '86 during retrace intervals of the scanning beam.

vAt the conclusion of. each retrace interval the carrier wave amplifier 8! is rendered inoperative and the-carrier wave amplifier 69 is again rendered operative under thecontrol oi the synchronizing signal source 83.- The described cycle of operation is then repeatedfor each scanning line.

In order more clearly to emphasize the manner in which apparatus in accordance with the present invention function to provide the informahon-regarding the average subject illumination 2,401,010 in addition to the information regard-ing the light and shade values of the subject; reference will be made to Figs. 2 to 7, inclusive.

Referring mw Particularly 2; t ere represented a picture area having a relatively CPI high average illuminationintensity. This area is divided into twoportions for the purpose of illustrating the principles underlying the 'inven;

. tion. Itis assumed that the left hand half of. 'the rectangular picture area 84 represents atelevision subject having. two light values. portion comprises alternate'vertical areasof which i the rectangles represent black picture elernents and the areas86 represent lighter picture ele,-..

ments such a f'or example, light gray, The right hand portion. BLof the picture area lilqis assumed to havejtheq'same light value as the area 88..

iconoscopey' e t t Referring now. to Ffig s. 6 and '7-the carrier wave energy derived irom theiconoscope opera. ated in accordance with the present invention is represented at 93. Bothfpositive and negative half cycles of the. carrier are modulated mamplitude' in accordance with. thelight and shade Fig. 3 illustrates a typical signal which is generatedby means of a conventionally operated iconoscope in scanning the picture area 840i Fig.

2 in a line extending from left to right. The i g maximum positive signal peaks 88 representthe black areas 85 and the negative peaks 89 represent the'light gray areas ,86 and 81. It is a char acteristic of an iconoscOPe, conventionally operated, togenerate thistypeof signal and since it portions 86 of Figs.

values o'fythe, picture areasliil andf9l, respectively, of Figs. 2 andA'. Consequently, both'po'se itive andnegative envelopes of the carrier wave correspond respectively to the signal wave forms illustrated in Figs. 3- and 5. Specifically, the.

I amplitudemodulation of both positive and nega- Y tive half cycles. oii the carrier wave. 93 ,'the alternating current 'derivedirom the output electrodes of the iconoscopeTproduces an average zero voltagejwhichis invariably related to theamplitud is oi'ian alternating current characterthe energy content of. a positive polarity is equal to the en ergy; content of anegative polarity forany given time interval, such as the scanning time for one line. Inasmuch as the proportion of the, total light grayareas to the total black areas of the or the wave irrespective of the averageilluniinationintensityof the television subject. The re-- sult is that"theinstantaneous amplitude oifjthey generated carrier wave always has the-samevalue relative jto "a fixed. reference voltage in corre ii spondence with the absolute brightness of ,the'

flelemental area being scanned. In'this manner picture 8.4.isthe ratio .of;3 to 1, the average zerovoltage ofthe generated alternating current signal is. disposed relative to the positive and negawhich will contain both the information regardtive voltage peaks in a manner such that the f proportion of thepositive voltage peaksvt'o the negative voltage peaks also is in the ratio of v3 Consider nowthe case where the average sub Ject illumination isrelativelyxlow as compared ,to that represented by thepicture :area 84. In

Fig. 4 there is illustrated a picture area of the same shape 'and dimensions as the area 84.. In

this case the left hand portion is the same as in e the area 84-, comprising alternate black strips 8 5 jand light gray strips 86. However, the rig ht' "hand portion 92 of the area!!! is black. It is evident that the average illumination of. the picf ture area 9| is considerably less thanthat of the picturearea 84 ofFig.2. i

Thesame general .type of video signal'is geny. erated to represent the left hand portion of the. area 9| asthat representing the area 185. This the developed voltage maybe demodulated if desired, to recover the modulating component ing the light and shade variations of the subject the information regarding the averagesubject illumination intensity. a

r Also, it has been determined in practicefthat the phenomenon known as shading, when operating an iconoscope in a conventionalmanner, is

ciency of jthesignal generzator. Additionallmfiit hasbeennecessary to provide iacilities ioifLeom-f -pensatin'g the spurious signal by introducing a condition is represented in Fig. "5 wherein the black strips 85 are represented by positive voltage peaks 88' and the light gray'strips" 86 'are represented by the negative voltage peaks 189'.

In this case, however. the proportionof'the total I light gray areasof thepicture Bito the total" black areas thereof is in the ratio of 1 toa3.- Con: sequently, the average zero voltage of'the gener ated alternating current signal representing the .picture area Si is disposed relative to the positive a and negative voltage peaks 88'; and 88f; inamanner such that thelproportion of the positive voltage peaks to the negative voltage peaks also is in e a the ratioof 1 to 3.

It is evident that the signals pf Figs. 3 and 5 i are not usable without modification" for the ac curate reproduction of the television subject. The modification required is the incorporation in the signals of the so-called D. C. component. It is well known, of course, thatthis component may" substantially entirely eliminated I by sjpr apparatus operating in accordance with the jin stantinventiom Shadingfis causedbythe f pro H duction ofspurious sig'nals incidental to the scan-' .ningiof the mosaiebyihe electron beam. Here- 'tofore, in order to minimize the. shading effects.

it has been commonpractice tooperatean icono: R

f scope with relatively small scanning bearn currents. Thisgpractice. however, ..reduces the em;

the spuriousshading signal.

It has ,been found thatby similarly shaped. signal [of opposite polarity to the invention described previously, the spurious shading signals are not present in the ".signal derived fromtheoutput circuit of the iconoscopelt For this reason itispossible to increas jthe'eiii ciency of the iconoscope as a signal generator by employing'a scanning beam of fmateriallygreater T i current intensity than heretofore has been possible. H I .While therehas been described what. at pr s, ent, is considered the preferredembodimeritof 1 the invention, it will be obvious to those skilled i in the art that various changes and modifications may be made therein without departing fromthe invention, and therefore; it is aimed in the ap-j pendedclaims to cover alljsuch changesand'modf ificationsas fall within the true spirit and scope of the invention. i

not be derived from a conventionally operated using the iooiioscope as acarrier wave modulator, in accordance with What is claimed is:

1. In a television signal generator, an image,

- means for modulating the intensity of the oathode ray at a carrier wave frequency, whereby to develop in said utilization circuit, amplitude modulated carrier frequency energy representing video signals, and means for periodically discontinuing the cathode ray modulation and for simultaneously impressing upon said utilization circuit carrier wave energy modulated in amplitude independently of video signals. s

2. In a television signal generator, an image analyzing tube having means for producing a cathode ray, a cathode ray intensity control circuit and an output circuit including an electrode anodically relatedto said ray producing means, means for deflecting said cathode ray relative to said anodic element, a utilization circuit coupled to said output circuit for the development therein of carrier frequency energy suitable for radiation, means for modulating the intensity of the cathode ray at a, predetermined alternating current frequency for thedevelopment in said utilization circuit of energy at said carrier frequency modulated in amplitude in accordance with video signals,- and means for periodically interrupting the modulation of said cathode ray and for simultaneously developing in said utilization circuit carrier wave energy having a predetermined modulation independent of said video signals.

3. In a composite television signaligenerator,

amplitude in'accordance with'video signals and a cathode ray image analyzing'tube having a ray.

associated withone of said electrodes and means for producing a concentrated electron beam to scan elemental areas of said mosaic, means for modulating the intensity of said electron beam at a carrier frequency during trace intervals, whereby to develop atsaid output circuit electrodes carrier frequency energy modulated in amplitude in accordance with video signals and including information regarding the average illumination intensity of a television subject, a

utilization circuit coupled to said output circuit electrodes, means for interrupting said electron scanning beam during retrace intervals, and means for simultaneously injecting into said utilization circuit carrier frequency energy modulated in amplitude independently of video signals.

5. A composite television signal generator comprising, an image analyzing tube having output including information regarding the average illumination intensity of a television subject, a video signal amplifier having its input circuit coupled to said output circuit electrodes, a television transmitter coupled to the output circuit of said video signal amplifier, means for coupling said carrier wave source to said video signal am- .plifler, and'means forenergizing alternately said two carrier wave coupling means, whereby to interrupt said electron scanning beam during retrace intervals and simultaneously to inject into said videosignal amplifier carrier frequency energy modulated in amplitude independently of video signals.

- 6. A composite television signalgenerator comprising, an image analyzing. tube having output circuit electrodes, a photoelectric mosaic associated with one of saidelectrodes, and means for producing a concentrated electron 'beam to scan elemental areas of said mosaic, a source of radio frequencycarrier wave, means including a first carrier amplifierfor couplingsaidcarrier wave source to said image analyzing tube to modulate the intensity of said electron beam during trace intervals at the frequencyof said carrier wave, whereby to develop at said output circuit electrodes carrier frequency energy modulated in amplitude in accordance with video signals and including information regarding the average illumination intensity of a television subject, a videosignal amplifier responsive to said modulated carrier frequency energy and having its .input circuit coupled to said output circuit electrodes, a television transmitter coupled to the output circuit of said video signal amplifier, means including a second carrier amplifier for coupling said carrier wave source to said video signal amplifier, and timing means for energizing alternately said first and second carrier amplifiers, whereby to interrupt said electron scanning beam during retrace intervals and simultaneously' to inject into said video signal amplifier carrier frequency energy modulated to a predetermined amplitude independently of video signals in order to develop at said transmitter a composite television signal including alternate video and synchronizing components.

7; A composite television signal generator comprising, an image analyzing tube having a pair of output circuit electrodes, a photoelectric mosaic associated with one of said electrodes and means for Dl'Odllchlg a concentrated electron beam to scan elemental areas of said mosaic, a source of radi frequency carrier wave, means including a first carrier amplifier for coupling said carrier wave source to said image analyzing tube to modcircuit electrodes, a photo-electric mosaic associat'ed with one of said electrodes and means for producing a concentrated electron beam to scan elemental areas of said mosaic, a source of carrier wave, means for couplingsaid carrier wave source to said image analyzing tube to modulate the intensity of said electron beam during trace intervals at the frequency of said carrier wave, whereby to develop at said output circuit electrodes carrier frequency energy modulated in ulate'the intensity of said electron beam during trace intervals at the frequency of said carrier wave, whereby to develop at-said output circuit electrodes carrier frequency energy modulated in amplitudein accordance with video signals and including information regarding the average illumination intensity ofa television subject, a multistage video signal amplifier responsive to said modulated carrier frequency energy and having its input circuit coupled to said output circuit electrodes, a television transmitter coupled to the output circuit of said video signal amplifier, means including a second carrier amplifier for coupling said carrier wave source home of the latter stages of said video signal amplifier, and means including a source of synchronizing signals for energizing alternately said first and second carrier amplifiers, whereby to interrupt said electron scanning beam during retrace inter vals and simultaneously to inject into said video signal amplifier carrier frequenc energy modulated to a predetermined amplitude independently of video signals in order to develop at said transmitter a composite television. signal including alternate video and synchronizing components. H i

8. A, composite television signal generatorcomprising, an image analyzing tube having apair of output circuit electrodes, a photoelectric mosaic associated with one of said electrodes and means for producing a concentrated electron beam to scan elemental areas of said mosaic, a source of radio frequency carrier wave, means including a first carrier amplifier for coupling said carrier wave source to said image analyzing tube to modulate the intensity of said electron beam during trace intervals at the frequency of said carrier wave, whereby to develop at said output circuit electrodes carrier frequency energy modulated in amplitude in accordance with video signals and including information regarding the average illumination intensity of a television subject, a multistage video signal amplifier responsive to said modulated carrier frequency energy and having its input circuit coupled to said output circuit electrodes, a television transmitter coupled to the, output circuit of said video signal amplifier, one of said video amplifier stages bep or ing biased so as to amplify said modulated carrier frequency energ in a manner to increase the modulation percentage thereof, means including a second carrier amplifier for coupling said carrier wave source to one of the latter stages of said video signal amplifier, means including a source of synchronizing signals for energizing alternate- 1y said first and second carrier amplifiers, where J by to interrupt said electron scanning beam during retrace intervals and simultaneously to inject carrier frequency energy modulated to a prede- Louis mm.

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