TagYISIOt1 SEPTEMBER, 1935 AND SHORT-WAVE WORLD

The Iconoscope is the invention of Dr. Valdimir K. Zworykin of the R.C.A. researchlaboratories.It has a re- markable similarity to the human eye. This simple description will be of in- terest as the Iconoscope is likely to be employed in one of the systems of high definition transmission which are to be inaugurated from the Alexandra Palace. A SIMPLE EXPLANATION

Fig. 1.The Iconoscope tube and OF THE ICONOSCOPE deflecting coils. COMPARATIVELY littleinformation has been How the Iconoscope functions will be understood by published on the Iconoscope, the reason probably reference to Fig.2. Here the metal plate is shown being that itisstill in process of development. edge on, and it will be seen that it is in two parts, the When Dr. Valdimir Zworykin, the inventor, introduced actual photo -electric mosaic and the back metal plate the device, he said " In ordinary television systems which Zworykin calls the signal plate. The narrow every point of the picture acts on a photo -electric cell neck of the tube and a part of the spherical bulb are for a very short duration of time.This time is of the metal -coated internally, this acting as a second anode order of one z,soo,000th part of a second.This dura- for the electron beam which is directed on to the photo- electric mosaic in the usual manner. Two local oscillators supply the energy to deflecting magnets which surround the neck of the tube.These can be seen in Fig.idetached from thetube.An image of the object to be transmitted is focused on the mosaic by a lens system, as shown diagrammatically in Fig. 2.The mosaic is, of course, systematically swept by the electron beam under the influence of the Electron framing and line -scanning " saw -tooth " currents ap- Beam plied by the coils. The cross-section of the electron beam which scans the photo -cell plate must be held within very accurate limits.It must be equal in size to the area of one Fig.z.-Diagram showing the operating principle of the Iconoscope. picture unit.The greater the number of elements into which the picture image is divided, the greater the tion is only obtained in the case of very good pictures. definition of the received image. During this period a photo -cell of the highest sensitivity will deliver only 6o electronstotheamplifiers, an Iconoscope amount so small that good amplification is impossible. Resolution " In the Iconoscope, the picture acts on the photo- Actually the resolution of the Iconoscope is consider- cellall of the time, and there is provisioninthe ably better than the rest of the system is capable of structure which collects the energy of the light, or, so transmitting.As a result of this, it is possible to scan to speak, memorises it and then transmits it, point by an area considerably smaller than the full size of the point.This involves a new principle for storing elec- Iconoscope plate before the resolution of the Iconoscope tricalenergy, which may be called the electrical becomes the limiting factor.This makes possible an memory.' " unusual flexibility in the use of the camera.By chang- The Iconoscope isa special form of cathode-ray ing the horizontal and vertical scanning amplitudes tube which is shown by the photograph, Fig. i.The simultaneously, the effect of moving the camera for- glass envelope is of a somewhat different shape from ward or away from the subject is obtained without the normal cathode-ray tube.The electron beam is actually moving the camera.By adjusting the posi- produced by an " electron gun " system in a similar tion of the scanning pattern to various sections of the way to that of the ordinary cathode-ray tube. The mosaic, the effect of turning the camera may also be novel feature is the square plate seen in Fig. i.This obtained. consists of a metallic coating on one side of a sheet An Iconoscope camera is shown by Fig. 3. The of mica.The other side of the mica sheet-the side partition a through the centre is an electrostatic shield exposed to the electron beam-is covered with a fine separating the picture -frequency amplifier from all other mosaic of minute particles of photo -electric material voltages applied to the Iconoscope.This shielding is deposited on the mica. quite essential due to the magnetic and electrostatic

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