US2241204A - Signaling system - Google Patents

Description

86 J. E. KEYSTON ETAL 2,241,204

SIGNALING SYSTEM Filed April 17, 1936 Mme/flora John Edgar Keys/on Leonard F. Broadway Patented May 6, 1941 UNITED STATES PATENT. OFFICE John Edgar Keyston, Hayes, and Leonard Francis Broadway, Hillingdon, England, assignors to Electric & Musical Industries Limited, Hayes, Middlesex, England, a company of Great Britain Application April 1'7, 1936, Serial No. 74,826

. In Great Britain April 17, 1935 a 1 i (Cl. 178-72) I l'Claim.

The present invention relates to cathode ray tube circuit arrangements for television and like purposes.

Cathode ray tubes are known in which an image of an object to be transmitted, such as a frame of a motion picture film, is projected on to a mosaic screen, the screen being scanned by a cathode ray from a suitable gun for the purpose of generating picture signals.

The mosaic screen may be constituted by a plurality of small, discrete photo-electric elements each having capacity to a common signal plate, or by a plurality of mutually insulated conducting elements, one side of the screen being made photo-electric and has an optical image of the object to be transmitted projected upon it, while the other side is arranged to be scanned by the cathode ray. Furthermore, the mosaic screen may comprise a plurality of mutually insulated conducting elements which are not photoelectrically active; in this case, an electron image may be focused on to the mosaic screen, by any suitable electron-focusing means, from a photo-electric surface on which an optical image of the object to be transmitted is projected. The invention is also applicable when the mosaic screen in the last-mentioned case takes the form, for example, of a sheet of mica, or other material which has a high resistance in the plane of the surface on which the electron image is focused.

It has been proposed in a television system utilising a transmitting tube embodying a mosaic screen to modulate the intensity of the ray at the frequency of a transmission carrier; for this purpose, carrier frequency oscillations have been fed to a control electrode forming part of the gun, the output of the device then taking the form of a carrier wave modulated by the picture signals. It has further been proposed to feed synchronising signals to the control electrode referred to above, in addition to the carrier oscillations.

It is an object of the present invention to provide a cathode ray tube circuit arrangement in which improved means are provided for effecting modulation of the electron beam.

According to the present invention, in a circuit arrangement embodying a cathode ray tube comprising a cathode, a screen, means for focusing electrons from said cathode in a narrow beam upon said screen, and two electrically separate electrodes arranged in succession along the path of the ray between said cathode and said screen, there are provided means for enabling modulating potentials of diiferent characters to be applied to saidtwo electrodes respectively.

In a preferred form of the present invention, a circuit arrangement comprises a cathode ray tube of the double acceleration type, that is, a tube in which electrons from the cathode undergo at least two accelerations during their passage from the cathode to the screen, and are subjected between two of said accelerations to a deceleration. Such a tube may comprise a cathode and a screen, such as a mosaic screen, and, arranged between the cathode and the screen in the following order, a cathode screen, an accelerator electrode, a modulator electrode and one or more anodes; in operation, the accelerator and the anode or anodes are maintained at suitable positive potentials relative to the cathode and serve to accelerate electrons from the cathode, the cathode screen and the modulator'electrode are maintained at negative potentials relative to the cathode, so that the modulator serves as a decelerator, and modulating potentials of different characters are applied between the cathode screen and the cathode, and between the modulator electrode and the cathode respectively.

When such a tube is employed in a television transmission system, an image of the object to be transmitted is projected on to the mosaic screen, and the electron beam is deflected by electrostatic or electromagnetic means, in known manner, so as to scan the screen. In such an arrangement, according to one aspect of the present invention, oscillations at a carrier frequency are applied between the modulator and the cathode, and synchronising ignals are applied between the cathode screen and the cathode, the output of the tube then being in the form of a carrier oscillation modulated both by picture signals and by synchronising signals.

The synchronising signals may be arranged to reduce the intensity of the electron beam to zero, so that the synchronising signals are represented in the modulated carrier by intervals of zero carrier amplitude.

The application of the carrier oscillations and the synchronising signals to different control electrodes has the important advantage over the known arrangement referred to that it can readily be arranged that there is substantially no coupling between the carrier source and the source of synchronising signals, and interaction between these sources can thus be avoided.

In some cases, it may be desired to maintain the level of the transmitted picture signal substantially constant; for this purpose, there may The invention will be further described with I reference to the accompanying drawing which shows, by way of example, a circuit arrangement according to the invention" embodying a transmitting cathode ray tube.

Referring to the drawing, the tube I has a cathode 2, a mosaic screen 3, and, arranged" beamplitude. Any known or suitable means may be provided for varying the amplitude of the cartween the cathode and the screen-,in' the: order a named, the following electrodes a cathodescreen 4, an accelerator 5, a modulator 6 and first and tifier. H and the cathode-of'tube l is con-nected to the join of resistances I5 and- IB. The accelerator 5 and the first and second anodes 5' and T are connected to points at progressivelyi'n creasing. positive potentials in the potential divider, and the cathode screen d is'given-a negative bias relative to the cathode 2 by connection to an adjustable tapping point. in resistance t6; the modulator 6 derivesa negativebias froman adjustable tapping point in a resistance H connected in shunt with resistance It. Carrier frequency oscillations are fed tomodul'ator 6 from source I8 throughtrans-former' l9, and synchronising impulses from source 20- are taken off from resistance 21 and appliedtocathode screen 4'. p

The synchronising signals are preferably fed to the cathode screen 4 in thenegative sense; and at such a level that they reduce the intensity of the cathode-ray to-zere, so that, in the signals set up across resistance l0; the synchronising signals are represented by periods of zero carrier rier oscillation applied to modulator 6.

The invention is not limited to the arrangement described by way of example above, and many modifications of the invention, within the scope of the appendedclaim, will occur to those versed in the" art;

We claim:

A television signaling system comprising a cathode ray image transmitting scanning tube, said tube having included therein means including an electron source to develop a cathode ray beam and a photoelectrically responsive mosaic electrode:- adapted? to receive a light image of which an electro-optical replica is to be produced at receiving: points and a signal plate element associated with the mosaic electrode, a signaling circuit connected with the signal plate electrode, means comprising a plurality of electrode elements: to accelerate and focus the developed cathode ray: beami upon the mosaic electrode, means to deflect the cathode ray beam in a predetermined traversal pattern relative to the mosaic electrode to: release energy to the signal circuit which is proportional. tothe brilliance of the optical image cast upon the mosaic, a source of" synchronizing signal energy, a. plurality of modulating electrodes intermediate the electron scurceand the mosaic and along the path of the electron beam, one of said modulating elec trodes being located nearer the electron source than oneof theaccelerating electrodes and the other of the modulating electrodes being located nearer the mosaicthan the said accelerating electrode, anelectrical connection to supply the generated carrier to one of the-modulating electrodes sothat the signal impulses in the signaling circuit are modulations ofthe said carrier frequency, an electrical connection to supply the synchronizing signals to the other of the modulating electrodes to suppress the cathode raybeam at predetermined intervals, said independent connections tothe modulatin electrodes being' suchthat direct interaction between the carrier'frequencyenergy sourceand the synchronizing signal energy source is'reduced' toa minimum value;

J OHN' EDGAR; KEYSTON. LEONARD FRANCIS BROADWAY;

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