US2227002A - Television transmission method - Google Patents

Description

DBC 31, 940- K. scHLEslNG-ER .2,227,002

TELEVISION TRANSMISSION METHOD Filed Jan. 7, 1956 2 Shef-zs--Sheel 1 I@ 3 P 17 IIL 7 i? 8 4% f 1 l -I f I l l 2 l VZ #5 l n Il l fnf-7 lo mfg Si I F{ Za FI -2b Z Dac 31, 1940- K. SCHH-:SINGER v2227,@02

TELEVISION TRANSMISSION METHOD Filed Jan. 7, 195e 2 sheets-sheet 2 Patented Dec. 31, 1940 PATENT OFFICE 2,227,002 v TELEVISION TRANSMISSION METHOD Kurt Schlesinger, Berlin, (Sierinany,` assigner, by

mesne assignments, to Loewe Radio, Inc., a corporation of New York Application January 7, 1936, Serial No. 57,870 In yGermany January 9, 1935 y 12 claims. (C1. 17e- 7.5)

Heretofore it has been customary to synchronise a television transmission by the iact that at the end of each line and at .the end of each picture there have been transmitted a short and 5 long impulse respectively in a certain direction,

which impulses exceed the image content signals as regards intensity. `'The reception of a transmission of this kind was then rendered posf sible by mean-s of a so-called amplitude lter, 10 i. e., by means of a device which allows the passage of current only above a certain surge value. The surge value of this amplitude lter was Vthen so adjusted in practice that the synchronisation signals, owing to their large amplitude, but not 'the image signals, were allowed to pass. In this way the synchronisation signalswere separated from the image currents.

A disadvantage of this method exists atwthe transmission end. A certain amplitude range mustv be reserved solelyfor the synchronisation signals. The transmitter, therefore, cannot be -controlled fully by the image signals alone. In practice two-thirds of the aerial current at the most can be employedfor the image signals, and the remaining one-thirdl must be reserved for the synchronisation signals. In the case ofweak reception images as such are certainly Iproduced, but the contents of the image are so weakly demodulated that nothing is `to be recognised. A 30` further disadvantage is the fact that strongY atmospheric interferences are always able 4to actuate the synchron-is'ing apparatus when their volume of sound exceeds the threshold of response of the filter.

The present invention eliminates these disadvantages by the time blocking method. The fundamental idea of this method resides Vin the following: Between the image-signal receiver and the synchronisation terminals of l the scanning apparatus there is provided an amplitude filter of a particular kind, lthe surge value of which is variable. This filter, as described in the following, is completely blocked for 90% of the `line period (blocking phase). During this period it 45 cannot vbe passed even by the most powerful reception amplitude, and no interferences are able t inuence the synchronisation. It is only just before the end of the line is 4reached that the surge value Iof the lter is differently adjusted. The filter is so biassed that it may now be penetrated by signals of normal recept-ion intensity. A passage of current does nevertheless still not yoccur (Waiting phase). It isvonly when the transmission during this waiting phase exceed-s a certain surge value that the amplitude lter is passed, and accordingly a synchronisation of the'scanning apparatus, takes place (ignition-pha-se). Shortly after the relaxation point of the scanning apparatus has occurred, and accordingly the Vimage point has been .thrown 5 back to the other edge of the image, the amplitude filter again returns to the initial condition,

`i.'e., to the blocking phase, and the operation is repeated.

The invention may best be understood byreferring tothe drawings wherein:v

Figures la and 1h show image areas for producing? picture `and synchronizingsignals,

`Figure 2a shows a curve indicating the relationship between light intensity and antenna current orcarrier amplitude, A

Figure 2b shows a wave form of the combined picture and synchronizing signals,

Figure 3 shows one form of the present invention, and

Figure 4- shows graphically the voltage variations which occur in the circuit diagram `shown in FigurelB. y

To the operation as described there "belongs a certain iorm of diagram of th-e radiated transmission,l i. e., a certain nature of the synchronisation signals at the edges of the image. Fig. 1a explains these conditionsin detail. It is assumed that an image with the image area l is given in positive fashion, for example as positive film. The transmitter is modulated with thisimage content in suchv fashion that a white point inthe image corresponds witha large aerial current, whilst a deep black point in the image causes the aerial current to disappear. The characteristic 2 of the transmitter in Fig.` 2a represents the connection between `the light intensity of the image H and the intensity of the aerial current-i. .I The point i=0 is accordingly reached inthe case of H=0. rThe transmitter, therefore,` is already modulated to the extent of 100% by the image content. The image area l in Fig. 1a is made approximately 10%smaller than the sectional area 3 on the Nipkow disc, which is determined by four image points 4. The edge resulting between the sectional area 3 and the image area l is'light to theextent of' onehalf by optical means; There is produced an inner margin 5 having a light intensity H5. There then remains an outer margin 6, in which any form of' lighting completely disappears (11:0). 'I'he aerial current diagram resulting upon 'the' scanning of a reproduction area of this kind is' traced lin Fig. 2b against the time. vThe time sections l, 8, etc., correspond in each case with a line peri-od. At the end of each line the scanning image point moves over the double edge 5/6. This is a time section I', 8', which amounts to 10% of the entire period I/8 of a line (edge period). Within this image margin there arises the edge signal. The edge signal commences with an intensity Hs corresponding with the inner margin lighted with this intensity in Fig. 2b. The edge signal terminates with the intensity 0 at that moment when the scanning image point passes into the outer margin 6 in Fig. la, because in this phase a lighting of any kind does not occur. TheV time at which this change-over from H5 to 0 takes place is designated tz in Fig. 2b. tz represents: ignition moment.

Fig. 3 shows an example of a receiver connection for receiving a transmission of thedescribed kind. A heterodyne receiver is supposed; the final tube of the intermediate frequency amplifier is designated 9. This tube is coupled with the twin grid detector tube il by means of the transformer I0. The conductivity of this tube decreases andthe anode gets more positive when the transmitted intensity increases. The anode is connected tothe control grid I6 of Vthe television tube I1 and takes care of the modulation of the electronic rayv preceding from the cathode I8 of the television tube. When the aerial current of the transmitter ceases, the anode potential of III becomes a minimum and is then merely-determined by the anode battery I3, independent of all accidental factors in the reception., The amplitude filter and time blocking devices according to the invention is the tube I4. Its cathode I5 is directly connected to the anode of the detector tube I I, its anode I9 to a counterpotential variable by means of the potentiometer 20. In this lead are inserted the transformers 2| and 22, which sepa-rate the synchronization impulses according to their timer duration, whereby the transformer 2| having a high natural frequency Itransmits the short lineimpulses an'd the transformer 22 the long frame change impulses to the input of Ithe line (or horizontal) relaxation oscillator 36 and the frame (or vertical) relaxation oscillator 31, respectively', the output of `which is connected to the deflecting plates. .-The operation and use of the transformers ZI and` 22 is well known in the art as, for example, in George Patent No. 2,100,279. The relaxation oscillators or beam deflection generators are shown schematically at 36 and 3'I since any satisfactory oscillator may be used. An example of s uch an oscillator is to be found in the U. S. patent to Tolson No. 1,999,378.

The feature of the present invention is the function of the twin grids 23, 213' of which 23 is associated withthe vertical or frame oscillator while 23' is associated with thehorizontal or line oscillator. They attend tothe time blocking ofthe amplitude lter 4I4 in thev following manner:

Through the medium of a very large series resistance24 and a ysmall coupling condenser 26 the control grid 23 is connected to the output of the/relaxation oscillator for deecting the cathode ray towards the synchronization edge of the image. As well known, this plate assumes inthe deflecting phase a positive D.C. potential of continuously increasingnamount. This potential lis added to the bias 28 imparted to the grid. via the leakage resistance 21. The negative bias 28 is selected of such value that mere- -mately 10% of the line period 33. `relaxation potential always remains constant, as

ly the last 10% of the increasing potential of the deflecting plate are able to impart to the grid a weak positive potential.

Fig. 4 shows the temporal course of the line relaxation oscillation such as passes from the left hand image edge 29 to the right h-and image edge 3|I .and assumes the amplitude 30 with posi- .tive sign. The bias is designated 3l, and is selected to be of such extent that the waiting phase, viz., the time section 32, amounts to approxi- Since the this is identical with the constant size of the image field in the receiver, and since the bias 28'is also a constant D.C. potential, the length of the waiting phase 32 may be adjusted to be constant. l*The curve 34 shows .the course adopted by .the grid potential of the tube I4 by the action l of this coupling with the plate circuit. Owing to the large series resistance 24 of approximately 10S ohms the grid bias does not continue to increase without limitation, but always remains at the most approximately l volt more positive than the particular cathode potential I5. Although, therefore, there is a weak positive grid-cathode bias during the waiting phase no current occurs in the anode circuit IIJ/20. Wearenow in the scanning period-which may readilyv be attained by adjustment of the frequency of the free relaxation oscillation at the receiverover the infner edge of the edge signal (edge 5, intensity H5, Figs. 1 and 2).` During this period the detector tube II is excited. In consequence the cathode I5 is biassed positively in relation to the anode, and although the control grid 23 is in a condition permitting passageno anode current is able to occur. It is only at the ignition point tz (Fig. 2b) when the scanning pointpasses over to the outer margin 6, that the aerial current disappears. The cathode then becomes negative in relation to the anode, and since moreover the grid is weakly positive in relation to the cathode a synchronising current impulse now passes through ithe filter I4. In this way, however, the image point is thrown to the opposite side of the image, i. e., the deilecting plate 25a again becomes negative to the extent of a few -hundred volts. The grid 23 of the amplitude filter I4 is again blocked in such'fashion that every kind of connection is interrupted between receiving element and synchronising element.

The present specification explains the principle of the invention with the `use of a possible connection system of an apparently very particular kind. There are numerous other possibilities of carrying out the idea according to the invention. The advantages of the method will, however, be readily apparent from the above remarks .and consist in the following: By adjustment of the surge value of the filter I4 (with the potentiometer 20) fundamentally every synchronisation value may be employed. It is not necessary, for example, to demand that .the aerial current is reduced completely to Zero in the dark margin 6. During the blocking phase the aerial current may assume any desired value. Operations may even be so performed that the synchronising amplitude is smaller in its absolute value than the'. maximum amplitudes occurring inthe image. This would certainly not result inV any advantages in practice, but shows the contradistinction between the time blocking method according to the invention and the method of pure amplitude separation employed at the present time. Interferences are wholly ineffec- -tive Vduring the blocking phase. The transmitter may be fully modulated. There mayoalso'ibe tran'smitteda negative. It is then merely neces- 'sa-ryto dispose the inner edge 5 onthe .opposite side of the'image and to .locate the `reproductionaarea `on the 'sectional area according to Fig. lb;` '.The photo-ampliiier is increased' b-yfa` phase- .reversing Lstage. Operations may naturally .also :beperformed with white instead of black outer eolges;` 4Thesynchronising impulses, as explained .in Fig. I1, donot'require `to be produced by optical lighting stages, but may Valso be` produced electrically. Numerous connection. systems are Aknown by `means of which short impulses can be produced. If an impulse oscillating in one direc- 4tion is Vpassedto a transformer with tuned natural oscillation and aperiodi'c damping., Lthere maybe derived from t'he secondary side thereof 4a single oscillationV period of a sine wave `which wouldv correspond with a doublesignal as just described fand producedy optically and peculiar ,to the presentmethod. i i

Theduration of the waiting phase, mustfbe equal to or. greater than the scanning period for `the marginal zone of the image. If this condition is not observed and if the Waiting phase is toosmall, the adjustment of the synchronisation is v,rendered more diiiicult. Otherwise the adjustment is no more difficult than upon reception of the transmissions heretofore. i

As regards thepractical execution of an amplitude lter with variable surge value, it may be 'added that `by the introduction of a second grid 23 a coupling may be performed withthe vertical plates of the television tube I1. With atube of thiskind having two grids there is solvedin the mostsimple fashion the problem` of independent adjustment of image-change signals and modulated by picture signals and synchronizing i impulses comprising a detector to demodulate -thecarrier to produce a series of picture and synchronizing signal impulses, a picture reproducing cathode ray tube including a cathode ray beam generating means, a beam modulating electrode and horizontal and vertical 'electronl beam-deflecting means, means for impressing the` picture signals and synchronizing impulses` upon the beam modulating electrode of the cathode ray tube, a synchronizing signal separator tube includinga cathode, an output electrode and a pair vof control electrodes, means forimpressing the produced series of picture and synchronizing signal impulses between the `cathodeand control electrodes of the separator tube, meansfor producing electrical energy variations forenergizing the horizontal and vertical beam ideiiecting means, a coupling between the output electrode ofy said separator tube and said last namedmeans for controlling said means in responseto the lsynchronizing signal impulses, means for biasing the separator tube control electrodes with respect to the cathode to a predetermined rblocking potential and means for coupling the pair of control electrodes individually to `the horizontal and ver.- tical beam delecting `means so thatthe normal blocking potential is reduced to a-threshold value determined by the deection so that thesepara.- tor tube is `rendered conductive only duringthe interval,when a synchronizing :impulse is 1received. f

2. .fi-television receiver for receivingia carrier modulated by picture signals and synchronizing `impulses comprislnga detector to demodulate the `carrier Vto :produce a series of picture signals and synchronizing'impulses, a Vpicture reproducing cathode rayf tube including a cathode ray beam generating means, a beam modulating electrode and electron beam deilecting means, means for .impressing the produced series of picture signals and synchronizing impulses upon the beam mod- -ulating electrode of the cathode ray tube, a synchronizing, signal separator tube including a cathode, .an outputelectrode anda control electrode, means for impressing the synchronizing signal impulses on the cathode of the separator tube, .means coupled to the output electrode of said .tube for producing beam deection voltage variations for controlling the electron beam defleetingl means ina predetermined operational .cycle in'response to the synchronizing impulses, means forbiasing the control electrode of the -separator vtube to va predetermined normal potential with respect to the cathode of the separator tubezto render the tube normally inoperative, 4anda capacitive connection between the control electrode of the separator tube and the beam delecting means to condition the separator tube in such a manner that the bias voltage is substantially neutralized at a predetermined time in the deilecton cycle so that the separator tube is rendered `conductive only during the interval when a synchronizing impulse is received.

i 3. A television receiver for receiving a carrier `modulated by picture signals and synchronizing :signals and the synchronizing impulses on the Jcathodeof the separator tube, means coupled to Vthe output electrode of said tube for producing beam deflection voltage variations for energizing the horizontal and vertical beam deflecting .means in response to the synchronizing impulses,

means for biasing the control electrodes at a predeterminedpotential with respect to the cathode of the separator tube and means for coupling the rpair of control electrodes to the horizontal and V,vertical beam deecting means respectively,

whereby `the separator tube is conditioned for conduction only in accordance with the time of receipt of synchronizing signalling impulses.

4. A television receiver wherein a series of picturesignals and synchronizing impulses are used to produce a television picture comprising a cathode ray tube, means for generating a beam of electrons in the tube, means for modulating the beam of electrons and means for deflecting the beam of electrons in substantially mutually perpendicular directions, deflection voltage generating meansr for energizing the beam deflecting means, a discharge tube including a cathode, a control* electrode and an anode, means for impressing the picture signals and synchronizing impulses upon the cathode of said tube, synchrolnizing impulse' responsive means connected to the .anode of said tube for controlling the deliection voltage'generating means, means .for biasing the 5. A'television receiver wherein a series of pic-I ture and synchronizing signal impulses are used to produceand synthesize a television picture comprising afcathode ray tube, means for generating a beam of electrons in the tube, means for modulating thebeam of 4electrons under the control of the said signals and means `for ,defiecting the beam of electrons in mutually perpendicular directions, means for generating electrical energy for energizing the beam deflecting means, a discharge tube includingna cathode, a control electrode and an anode, means for impressing at least the synchronizing signal impulses upon the cathode of said tube, means connectedrtothe anode of said. tube and responsive to the synchronizing signal impulses for controlling the deflection energy generating means, means for biasing the control electrode to a predetermined potential relative to the cathode to maintain said tube normally inoperative and means for coupling the control electrode to the deflection energy generating means to supply to said tube an auxiliary bias of oppositel polarity which reaches a maximum immediately prior to the time of the arrival of each synchronizing impulse and is of a lesser magnitude than the rst named bias so that thesaid tube is rendered conductive immediately upon and only during intervals when synchronizing impulses'are received.

6. A television receiver wherein a series of picture signals and synchronizing impulses are used to produce a` television picture comprising a cathode ray tube, means for generating a beam of electrons in the tube, means for modulating the'beam of electrons and means for deflecting the beam of electrons in substantially mutually perpendicular directions, deflection energygenerating means for energizing the beam deflecting means, a discharge tube including a cathode, a control electrode and an anode, means for impressing the synchronizing impulses between the cathode and control electrode of said tube, synchronizing signal impulse responsive means connected to the anode of said tube for controlling the deflection energy generating means, means for biasing the control `electrode to a predetermined negative potential relative to the cathode to normally prevent conduction in the tube, and meansA including an electron storage means vfor coupling the control electrode to the deiiection energy generating means whereby the bias on said tube is reduced at a time immediately prior to the receipt of a synchronizing impulse to a value such as to renderA the tube responsive t the synchronizing impulses only during a time interval approximating the time of arrival of each synchronizing impulse.

7. A television system wherein a series of picture signals and synchronizing impulses are used `to produce a television image including a picture .producing cathode ray tube, means in said tube ing impulses for controlling the deflection energy generating means, means for applying the series of picture signals and synchronizing impulses between the cathode and the control electrode of said tube, means for biasing the control electrode at a predetermined potential vrelative to the cathode to normally prevent the flow ofY electronic current through the tube, and

deflection energy generating means whereby the vbias 4on said tube is so reduced as to render the tube responsive to the synchronizing impulses only during a time interval approximating the time of arrival of each synchronizing impulse.

8. A ktelevision system wherein a series of picture signals and synchronizing impulsesare used to produce a television image including a picture producing cathode ray tube, meansior generating a beam of electrons in said tube, means for modulating the intensity of the beam of electrons, means for deflecting the beam of elec- Vtrons in substantially mutually perpendicular fdirectons, relaxation oscillator deflection voltage generating means for energizing the beam deflecting means, a discharge tube including a cathode, a control electrode and an anode, means connected to said anode responsive to `syn chronizing impulses for controlling the deflection voltage generating means, means for applying the series of picture signals and synchronizing impulses to the cathode o said tube, means for biasing the control electrode to a predetermined negative potential -relative to the cathode normally to prevent thev ow of electronic current 'through the tube and means for coupling the control electrode to the deflection voltage generating means whereby 'the discharge tuber is conditioned for conduction immediately prior to the application of a synchronizing impulse.

9.'In a'television system wherein a series of picture signals and synchronizing impulses are received and used to control and synthesize respectively the production of an electro-optical image, an image producing cathode ray tube having a target element, means in said tube for generating a beam of electrons and for directing the beam upon the target, means for modulating the intensity of the beam of electrons to control the intensity of the electro-optical images developed on the target, means for deecting the beamof electrons in substantially mutually perpendicular directions, deectionenergy generating means for energizing the beam deecting means, a discharge tube including a cathode, a control'electrode and an output electrode for separating the synchronizing and picture signais, means connected to said output electrode and responsive to the separated synchronizing impulses Afor controlling the deiiection energy generating means, means for applying the series .means for coupling the control electrode to the,r

of picture signals and synchronizing impulses between the cathode and control electrode of said tube, means for biasing the control electrode to a predetermined negative potential relative 'tothe cathode normallyto prevent the flow of electronic current through the tube anda storage means for coupling the control electrode to the beam deflection energy generating means to reduce the magnitude of the applied bias to a predetermined 4minimum value which is attained at a time period immediately prior to the normal period of receipt of synchronizing signal impulses whereby the discharge tube is rendered conductive onlyupon the application of synchronizing signal impulses thereon which serve to synthesize the electro-optical image.

iQ. A television receiver including means for amplifying' a radio frequency carrier amplitude tion cycles, a discharge tube including a cathode, a pair of control electrodes and an output electrode, means for impressing the picture signals and the synchronizing impulses between the cathode and control electrode of said discharge tube and also upon the electron beam modulating electrode, synchronizing impulse differentiating means connected to the output electrode of said tube for controlling the operation of the beam deflection generators to maintain the prel determined cycles under the control of received signals, means for biasing said control electrode .relative to the cathode to a predetermined negative potential sufficient normally to prevent con-` duction within the tube, and capacitive means for separately coupling the control electrodes to each of the beam deflection energy generators so as ultimately to reduce the bias to predetermined threshold value at a time immediately preceding the arrival of synchronizing impulses whereby the tube becomes substantially instantaneously conducting at time periods when synchroni'zing impulses are impressed thereon.'

1l. A television receiver including means for amplifying a radio frequency carrier amplitude modulated by a series of `picture signals and synchronizing impulses, detector means for producing demodulated picture signals and synchronizing impulses, a picture reproducing cathode ray tube including means for producing a` beam of electrons, means for modulating the .beam of electrons, means for deilecting the beam in a vertical direction and means for deecting the beam in a horizontal direction, vertical and horizontal beam deection generators connected respective- 1y to the vertical and horizontal beam deflecting means, a discharge tube including a cathode, a pair of control electrodes and an anode, means for impressing thel picture signals and the synchronizing impulses upon the cathode of said tube and upon the electron beam modulating electrode, synchronizing signal impulse differentiating means connected to the'anode of said tube for controlling the operation of the beam deflection generators, means for biasing said control electrodes to a predetermined negative potential relative to the cathode to normally prevent conduction of the tube, and means includ.- ing condensers for coupling the control electrodes respectively to the beam deflection generators whereby the bias on said tube is reduced during Y each deflection cycle in order that the-tube will become conductive only when synchronizing impulses are impressed thereon.

l2. A television receiver including means for amplifying a radio frequency carrier amplitude modulated by a series of picture signals and synchronizing impulses, detector means for producing demodulated picture signals and synchronizing impulses, a picture reproducing cathode ray tube `including means for producing a beam of electrons, means for deflecting the beam in a vertical direction and means for deilecting the beam in a horizontal direction, vertical and horizontal beam deiiection'generators connected respectively to the vertical and horizontal beam deflecting means, a discharge tube including a cathode, a pair of control electrodes and an anode, means for impressing the synchronizing impulses between the cathode and control electrode of said tube, synchronizing impulse respon` sive means connected to the anode of said tube for controlling the operation of the beam deflection generators, means for biasing said control electrodes to a predetermined potential relative to the cathode normally to prevent conduction within the tube, and means for coupling the control electrodes to the beam deflection generators whereby the control electrodes will be made less negative with respect to the cathode at intervals immediately preceding the arrival of synchronizing impulses.

KURT SCHLESINGER.

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