US2186742A - Television and like transmitting system - Google Patents

Description

1940; E. L. (3. WHITE 2,186,742

TELEVISION AND LIKE TRANSMITTING SYSTEM Filed March 5, 1936 2 Sheets-Sheet 1 T To ScArmmz;

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uTEIlEVISION AND LIKE TRANSMITTING SYSTEM v Eric Lawrence Gasling White, Hillingdcn, England, assignor to Electric & Musical Industries Limited,,Hayes', Middlesex, England, a company of Great Britain Application March 5,

1936, Serial No. 67,258

' In Great Britain March 18', 1935 6 Claims.

The present invention relates to television and like transmitting systems of the kind in which synchronisingsignals are transmitted in intervals between trains of picture signals. Y

In systems of'the kind referred to, :it is usual to provide .agenerator of master timing-signals, these signals being. used both to control the scanning process at the transmitter and for producing synchronising signals for combination with the picture signals to be transmitted; the synchronising signals are used to control scanning at a receiver.

. It is sometimes inconvenient to arrange that.

1 scanningat the transm'itter should take place at signals derived-from the master signals are su- 'perimposed upon the picture signals. In such cases, themaster signals have to travel an electrical distance, say d, to the scanning point, and the picture signals have to travel back a distance which is also generally equal approximately to d tothe point where the synchronising signals are impressed on the picture signals. Usually, :the

5 superimposition of *the synchronising; signals upon the picture signals is effected at a point' close to the master generator. {It is thus clear that the effect produced by the master signals on the picture signalsis delayed relative to the synchronising signals by the time takengby sigfiial; travelling a distance approximately equal 0 cl. a

It may also be desired toprovide a plurality of scanning points at different electrical distances scanning points in any desired proportion for transmission. In sucha case, the delays in the signals :from the various scanning-points are different from one'another.

-It -is the object of the present .invention to provide means for avoiding-or reducing the dif- -ficu1ties out1ined above.

television. or likesyst'em of the kind in which synchronising signals are transmitted in intervals between trains of picture signals, and in which scanning is effected at a scanning point- -at. the transmitter under the control of master signals from a master generator, synchronising signals .generatednnder the eontrol of said mas- "ter'signals being combined with picture signals vfro'msaid scanning point ata superposition point the. electrical distance of whichfromsaid. master a point -close tothe mastertiming-signal gen-z erator or to the point at which synchronisingv from the master generator and to transmit. at I will signals from any one of' these scanning points, .or :to combine .signalsfrorn the several {I'he present invention accordingly provides a generator by way of the synchronising impulse generator is different from the electrical. distance between the superposition point and the master generator by way of the scanning-point,

the system being characterised in that means are provided for compensating for the effect upon the relative phase of said picture signals :andsynchronising-signals. of. the *diflference between said distances. 1

I Usually thesaid superposition point is closer to the master generator than is. the-said scanning point, and in such a case .a suitable-delay'network may be provided between the master gen erator and the superpo'sition point.

ted vfromthe master generator ;to the scanning point usually comprise signals-of line frequency and signals of frame frequency, although in some cases only one frequencyfis required.

Where thereare a plurality of difierent scanning-points'at different distances irorn the master generator,- a network vgiving-. adelay atleast as great as thatexperiencedby'fsignals travelling to and irom the furthest scanning point :r'riay be provided between the master generator .and 5 the said superposition point, means being then provided whereby signals from said master gen- It will be understood that the signalstransmiterator .for "controlling the scanning at any of I the several scanning points mayberderived from at frame frequency together with a series'jof pulses at "line frequency, and these are "fed into one end of a delaynet'work comprising in this example series .inductances L and shunt condenerator indicated by G generates a series of pulses sers C. "signalsifr'om the other end of the net- ".work are fed'by lead S to the superposition point at "which. synchronising signals are superposed .upon picture signals. A plurality for scanning points is employed, 'each of which uses,-for example, a sci-called Iconoscope that is to say, a cathode ray tube comprising a mosaic screen of photo-"sensitive elements upon whch an image to be transmitted is cast and which is scanned by a cathode ray. The scanning circuit of each Iconoscope is connected to the arm of a multiway switch; two such switches S1, S2 are shown, the scanning circuits being connected to the switch arms by leads I1 and I2 respectively, The switches S1, S2 etc. enable the signals from the generator G, which are to be applied to the scanning circuits, to be taken from a desired suitable point along the delay network, the desired point being determined by the length of the lead conmeeting the scanning circuit with the network.

The generator G, network L, C, switches S1, S2,

etc., and the apparatus at the superposition point are usually arranged close together, and each of the Iconoscopes may then be connected to this apparatus through a multi-core cable containing the lead I1 or I2 and a lead for conveying the picture signals from the Iconoscope to the superposition point. The proportion of picture signals applied from each Iconoscope to the superposition point may be adjusted in known manner by means of suitable fade switches.

In one example, the delay network has 12 sections and is arranged to have a cut-off frequency of 1 megacycle per second, the time delay per section being then 0.32 micro-second. If the average velocity of the signals along the cable in each direction is 2x10 kilometers per second, each section will correspond in time delay to 32 metres of cable and will be suitable for a maximum length of cable, on any of the associated Iconoscopes, of about 400 metres. Where there is provided a number of Iconoscopes with cables of different lengths, these lengths are preferably arranged to be integral multiples of the length corresponding in time delay to one section of the network.

If desired, separate delay networks can be provided for the line and frame frequency pulses.

The pulses arriving at the Iconoscopes may be used in known manner to control the generation of saw-tooth oscillations which in turn are used to deflect the ray over the mosaic screen. They may also be used to provide black out pulses which are applied to a suitable control electrode and serve to cut off the ray during the return strokes. In a preferred arrangement, however, thesaw-tooth oscillations are generated at a point close to the switches S1, S2, etc., and transmitted down the cables to the Iconoscopes. The .picture signals generated are in the form of trains of picture signals with intervals between trains and the phase of these intervals will be determined by the pulses received from the generator G.

v If the correct tapping point on the delay network is selected for the particular length of cable in use, the time by which these intervals are effectively delayed, due to the transmission of signals from G tothe Iconoscope and the transmission of the picture signals to the superposition point, is equal to the delay experienced by the signals travelling along the network from G to the superposition point.

The network, instead of consisting of lumped impedance elements L and C as shown may be constituted by a distributed impedance member such as a continuous cable which may be suitably coiled so as .to occupy a conveniently small space. A suitable number of tapping points is brought out to switches S1,S2, etc., as before.

Where it is not desired to havea number of completely independent scanning circuits for the several Iconoscopes, a circuit such as is shown in Fig. 2 may be used.

A single master scanning circuit MS is provided, from which can be taken scanning oscillations of saw-tooth or other suitable wave form to control the scanning process; master timing signals from the generator G are employed to control the generation of the scanning oscillations. A delay network B is connected to the output on the circuit MS and tappings are connected from this network B to a plurality of switches of which two, S1, S2 are shown, which permit connection to be made between the scanning circuit of any one of a number of Iconoscopes and any one of a number of points along the network B. A stage of amplification is preferably arranged in each of the scanning circuits at the Iconoscopes for the scanning oscillations.

The generator G is also connected through a second delay network A to the superposition point by the lead S. The network A is arranged to provide a delay at least equal to that caused by the longest cable to be used between the master scanning circuit MS and any of switches S1, S2, etc., and the length of cable used to any Iconoscope connected to S1, S2, etc., can then be compensated for bysuitable adjustment of the corresponding switch S1 or S2, etc.

In this example, the black out pulses may be generated from the scanning oscillations either at each Iconoscope or at the end of the associated cables near to the master circuit MS.

Furthermore, a second set of conductors to convey impulses to provide black out may be taken from tappings on network A to a further set of suitable switches and thence to the Iconoscopes. These further switches may be ganged with the corresponding switches S1, S2 so that black out impulses and scanning oscillations for any Iconoscope are taken from corresponding points on the networks A and B respectively.

A further arrangement according to the invention, which is particularly suitable for use in interlaced scanning'systems such as are described in United States application Serial No. 38,524, is illustrated in Fig. 3.

A generator MO provides master oscillations at twice the line frequency which are fed to a generator SPGI of synchronising impulses of relatively long duration and twice the line frequency through a delay network DI. Oscillations from master generator MO are also fed through a frequency-divider FDI, which divides the frequency of the applied oscillations by a factor of 2, to a second delay network DII, from which delayed impulses at the line frequency are taken to a second generator SPGII of synchronising impulses of linefrequency and relatively short duration.

A second frequency divider FDII arranged to divide the frequency of applied oscillations by a factor of 405 is fed with oscillations from master oscillator MO, and divided-frequency oscillations from network D11 and frequency-divider FDII are fed to a generator SG, which provides impulses for use in the suppression of spurious signals which may be generated by the "Iconoscope.

Oscillations from network D11 and frequency divider FDII are also fed to a generator ISG of scanning oscillations for the Iconoscope, to a generator BPG of black-out pulses for use at the Iconoscope and to a generator TG of tiltcorrection oscillations; the latter are employed to correct for a form of distortion introduced by --of said synchronising signal generator ffor com- 'pensating for the difference between said two distances.

ithe Tconoscope, which manifests itself as a spurious signal superimposed on the picture signals. 1

Two further delay networks DIII and DIV are fed respectively with oscillations from generator ISG and pulses from generator BPG. Network -DIII feeds one conductor CI of a cable CB, which passes to'the Iconoscope, through an amplifier and output stage AI, while network DIV feeds a second conductor CII of the cable through an output stageAII. The third conductor 0111 of cable CB serves to convey picture signals from the 'Iconcscope to the superpositionpoint, and

synchronising impulses are also fed to that point from generators SPGI and SPGII.

The delay introduced by network DI is arranged to be equal to the maximum delay introduced by the Iconoscope cable; The master oscillations fed from M0 to FBI are delayed less means, situated at a scanning point, for scanning an object of which an image is to be transmitted to generate trains of picture signals having spacing periods between successive trains, a master generator for generating master controlling signals, means for utilising said master signals to control the operation of said scanning means, a generator of synchronising signals of a frequency which is the same as the frequency of recurrence of said trains, means for utilising said master signals to control the operation of said synchronising signal generator, means for superposing said synchronising signals upon said spacing periods at a superposition point the electrical distance of which fromsaid' master generator-by way of said synchronising signal generator is different from the electrical distance between said superposition point and saidmaster generator by way of said scanning point, and means for compensating for the difference between said two dis-- tances.

2. A picture transmission system comprising means, situated at a scanning point, for scanninganiobject of which an image is to be transmitted to generate trains of picture signals having spacing periods between successive'trains, a master generator for generating master controlling signals, means for utilising said master signals to control the operation of said scanning means, a generator of synchronising signals of a frequency whichis the same as the frequency of recurrence of said trains, means for utilising said master signals to controlthe operation of said synchronising signal generator, means for superposing said synchronising signals upon said spacing periods at a superposition point the electrical distance of which from said master generator by way of said synchronising signal generator is less than the electrical distance between said superposition point and said master generator by Way of said scanning point, and a delay network arranged in the path from said master generator to-said superposition point byway '3. A picture transmission system comprising means, situated; at a scanning point, for scanning an object of which an image is to be transmitted to generatetrains of picture signals having spac. ing periods between successive trains, a master generator'for generating master controlling signals, means for utilising said master signals to control the operation'of said scanning means, a generator of synchronising signals of a frequency which is the same as the frequency of recurrence of said' trains arranged closely adja-' cent said master generator, means for utilising a said master signals to control the operation of V i said synchronising signalgenerato-r, means for superposingsaid synchronising signals upon said spacing periods at a superposition point the electrical distanceof which from said mastergenerator by way of said synchronising signal generator is less than the electrical distance between said'superposition point andsaid master generator by wayof said scanning point, a first delaynetwork arranged between said synchronising signal generator and said superposition point, anda second delay network arranged between said master generator and said scanning.

point. v

4. In a television transmission system in which the scanningunit is located at a point remote from the synchronizing signal generator, the method of transmission which comprises the steps of developing a master control signal, controlling the scanning synchronism by means of said master control signal, developing trains of video signals in accordance with the light values of which bears a definite relationship tothe ratio of the distance along the electrical path fromthe point of generation of the master control signal to the point of superposition of the video and synchronizing signals to be transmitted by each of the two paths of transmission.

'5. A picture transmission system comprising means situatedat a plurality of scanning points for scanning objects of which an image is to be transmitted to generate trains of picture signals having spacing periods between successive trains, a generator for generating master controlling signals located at different electrical distances from the plurality of scanning means, means for utilizing said master signals to control the operation of said scanning means, a generator of synchronizing signals of a frequency which is the same as the frequency of recurrence of said trains,

means for utilizing said master signals to control the operation of said synchronizing signal generator, means for superpositioning said synchronizing signals upon said spacing periods at a. superposition point the electrical distance of which from said generator by way of said synchronizing signal generator is less than the elec- 'trical distance between said superposition point and said master generator by way of any of said scanning points, a delay'network arrangedin the path from said master generator to said superposition point by Way of said synchronizing signal generator for compensating for the difierence between said two distances, said network being arranged to be capable of introducing a delay at least as great as that experienced by master signals travelling from. said master generator to the farthest of said scanning points and thence to said super-position point, means for enabling master signals to be taken off from any of a plurality of tapping points in said network, and means for feeding master signals taken ofi from said tapping points to any one of said scanning points at will 6. A picture transmission system comprising means situated at a plurality of scanning points for scanning an object of which an image is to be transmitted to generate trains of picture signals having spacing periods between successive trains, a master generator for generating master controlling signals, means for utilizing said master signals to control the operation of any of said master generator by way of said synchro-z nizing signal generator is less than the electrical distance between said super-position point and said master generator by way of said scanning point, a first delay network arranged between said synchronizing signal generator and. said super-position point, a second delay network arranged between said master generator and any of said scanning points, and means for connecting any of said scanning points to any one of a.

plurality of tapped points in said second delay network.

ERIC LAWRENCE CASLING WHITE.

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