US2090004A - Televisor transmission system - Google Patents

Description

Aug. 17, 1937. w. ILBERG V 2,090,004

' TELEVISOR TRANSMISSON SYSTEM Filed Dec. 6, eso

a u a a a L MIE/FIER R MTR I\NVENTOR WALDEMAR meze BY *g ATTORNEY Patented Aug. 17,. 1937 e z L z,o9o,oo4

' 'mmvson' TRANSMSSION SYSTEM Waldemaliber-g, Berlin. Germany, assignoto Telei'nkcn Gesellschaft fr Drahtlose Teleg'aphie m. b. H., Berlin, Germany, a. corporatlon of Germany Application December e; 1930, Serial'No. 500.457 In .Germany December 11, 1929 The present invention relates to television systems and particularly to television systems wherein the Braun tube constitutes the medium by which the received picture is rebuilt. 'The sugw chosen sohigh that no spatial' dissolution or integral 'eflectupomthe eye, inside this pictureelement, will -correspond to its brightness. Hence,

gestion has repeatedly been made in the prior art to utilize a Braun cathode-ray tube for the recreation or recording of the picture at the receiving end oi' a televisor transmission system. such systems have been proposed by Dieckmann and Glage, Rosing, Schmierer, and others.

- With such a system a sharply concentrated or focussed cathode-ray pencil is caused to impingeupon a fluorescent screen, and this pencil, by suitable electrostatic or'electromagnetic defiecting means, is directed successively along definite paths corresponding to the sequence of scanning or exploration of the picture 'elements at the sending end over the picture field. So long as a mere black-white contrast picture transmission without half-tones is dealt with, intensity control of the constituent picture units or elements may be insured in this scheme by always switching the current leading the cathode-ray pencil in or out completely at the correct instant by control actions sent out from *the televisor transmitter equipment.

However; if an attempt is made to thus obtain transmission or reproduction 'of half-tones as is mosty imperative in practical television transmission, the above arrangement falls to operate satisfactorily. The undelying cause is that quantitative alterations of the feed current of a Braun tube 'which might be insured by an amplifler inserted in the circuit will invariably result also in a changing potential fall across the dlscharge sap and thus varying velocities. of the cathoderay particles or electron stream. This, in tum, preciudes' regular distribution of the picture points since the size of defiections caused in the electrons by'the electrostatic or electromagnetic field depends upon the speed thereohso that intensity control and coordinate control are interdependent.

This dimculty is to be avoided according to the present invention by the principle hereinafter to A be disclosed in that'recourse is had to time modulation rather than amplitude modulation. For this purpose the method o! operation is to be suchthat the Braun tube is traversed by current of a very deflnite strength which is always completely switched in and offwithout intermediate valuesoi' the current being. allowed to flow during 'appreciable time intervals. 'Inside a picture'` unit or element the relationship between the time oi' connection or flow and the duration of current' dlscomiection is to be so chosen thatthe the rate ol switching ,of the current' must be rtain minimum threshold value.

' tions are rectifled and thus converted into direct current impulses as far as feasible of rectangular discontinuity is occasioned owing to the coordinate motion of the fluorescent spot. In other words. the swltching frequency or. rate should be 4 *at least ,as high as, or, better still, higher than,"

the maximum still analyzable fequency' orthe illustrates the i by way of a photo-electric cell 2, the latter being infiuenced by the brightness 'of the original copy.

.As .the photoelectric cell 2 is 'illuminated, intermittent discharges are-set up in 'the glow-dischargegap in well-known manner, and the time 'sequence or time interval thereof, thatis, the' time sequence of the discharges, is approximately proportional to the luminous intensities striking the photo-(Electric cell 2: 3 connected in parallel relation to the glow-discharge gap allows of suitable adjustment of the frequency of these discharges. By amplifler means 4 and 5 the current impulses arising inside said gap are amplifled and radiatd off by the transmitter 8 in the form of picture impulses.

'The receiver, apart from a demodulator and amplifier 'l is conveniently equipped with suitable limiting means or a manipulator device 8 adapted A variable condenser to restore au incoming picture impulses or signals to the' same potential amplitude in spite oi' such fading effects as may have acted thereon over the 'air route in radio transmission. restoration to like potential values being imperative for the use of the modulation principle here disclosed. The 'manipulator 8. asls well known irom'the prior art, may',for instance, comprise 'a wave generator the oscillations of which are released locally by such incoming impulses as exgeed a cer- These 'oscilla- 'shape, and .these rectanguiar direct' current impulses in turn feed the discharge gap of the Braun tube n either directlyor else by way of a direct V current amplifier stage's. The Braun tube receiver o compris'es the usual cathode ll and anode H and a tubular member |3 for concentrating the electron stream i& which is' directed toward the fiuorescentscreen IS.. For controlling e vided. Each of these sets of plates maybe 'connected in any desired manner to a synchronizing source so as to produce a movement oi' the cathode ray pencil M which will correspond in posi tion to the position of each elemental area of the transmitter as scanned.

If necessary, a-residualcurren't may be allowed during the dark periods provided they do not occasion an appreciable brighten ihg of the ,fluolorescent screen. I

` Having now described myinvention, what I claim and desire to secure by Letters Patent is the following:

1. In a television receiving system wherein a 15 cathode ray tube is used as the electro-optic'al image reconstructing device, the method oi! reproduction which comprises receiving, rectifying and amplifying television signals, limiting the amplitude of all ot the signals toa constant value 20 to produce time modulated representations of the received signals, and interruptlng by the time:

4 35 the signals into visible representations, and

.means tor impressing the amplitude limited time modulated signals upon the control circuit oi' the cathode ray tube to produce electro-optical representations during the presence of signals 40and to prevent electro-optical representations during the absence oi' signals. I c

3. In a cathode ray television system, the method of reception which comprises receiving and rectifying incoming signalling impulses correi sponding to television image signals, limiting all rectifled signalling impulses to equal amplitude.

developing an electron ray, -controlling the con-` tinuity or interruption of the developed ray by .the rectifled and limited signals, and-controlling ,50 the position of the observable efl'ect produced by i the cathode ray stream as 'controlled and interrupted by the signalling impulses.

4. In a cathode ray television system, the method c! reception which comprises receiving and 55 rectifying incoming signalling impulses corresponding to television'image signals,-limiting all rectified signalling impulses to' equal amplitude, 'developing an electron .ray. controlling the continuity or interruption of the developed ray by po the 'rectifledpnd limited signals, and controlling the' position of the observable eflect produced by the signal !rom the :controlled cathode ray stream. v i

5. The method of controllingobservable" ef- 05 !ecte in a cathode ray device which comprises generating. a cathode -ray stream, p'roiecting the generated stream toward a nuorescent' window to produce'` thereon an observable eflect, deflecting the cathode ray stream along a plurality of paths F hearing 'an angular relationship to each other to `control the position or the observable ei'fect produced, and producing an intensity control of the observable eflect by interrupting the projected- 76 `othxe ray stream !or time intervak van/ing in ating a cathoderay stream, projecting the gen- 5 erated stream toward a fluorescent window to produce thereon an observable eflect, deflecting the cathode ray stream along a plurality of paths hearing an ang'ular relationship to each other to control the position of the observable eflect produced, and producing an intensity control of the observable eflect hy periodically interrupting the cathode .ray stream in its passage toward the fluorescent window for time intervals of varying duration proportionate to varying intensities of light and shadow to be represented. v I

7. In an image reproducing device a cathode ray tube `having a source of cathode rays and a screen upon which the cathode rays areadapted e to impinge to produce observable effects, means cooperating therewith to deflct the developed cathode rays along a plurality of paths hearing an angular relationship with respect to each other so as to control the position of/ the observable eflects produced, means tor receiving signals of .25 which an electro-optical indication is desired, means for limiting the amplitude of all of the received signals to a single predetermined value, and means for applying &he amplitude limited signals to pass and interrupt the developed cathode ray in its passage .between 'the source and the screen in` accordance with'the presence or,

absence of voltage output. from said limiting means.

8. In a cathode ray device, a source of cathode rays, a screen upon which said cathode ,rays are adapted to produce observable effects, means for .defleoting the cathode rays along a'plurality ot paths hearing an angular relationship with respect' to each other to control the position of 40 the observable ei'fect produced upon the screen', an electrode interposed between' said source of cathode rays and said screen, means for converting received signals into constant amplitude time y modulated signals,`and means for supplying to the said electrode said time modulated signal potentials appearing in the output 'circuit of said converting means so as either to block-periodically the` ray in its passage to the screen or to permit the ray developed to pass to the screen.

9. A system for producing images having the efl'ect of varying intensity throughout which' comprises a cathode ray device having 'therein a source for producing cathode rays and a screen upon which said cathode rays produce observable images, means for causing the cathode ray t'o sweep across the screen at a predetermined rate, and means tor passing or interruptingthe cathode ray in its path toward said screen with a time rate of passage or interruption of the eo stream proportionatetg the intensity which is-to be observed upon the screen.

10. A system for producing images having the eirect of varying intensity throughout'which co'mrises 'a cathode ray device having therein a urce for producing cathode rays and a screen -upon which said cathode rays produceobservable "images, means tor causing the cathode ray to sweep across the screen at a predetermined rate,

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