From the History of TV

1. The word television comes from the Greek word “tele” which means “far”, and the Latin word “visio” – “seeing”. It enables us to see stationary and moving objects at great distances. We know television to be widely used both in everyday life and in industry, in scientific work, etc.

2. The progress of television since 1929 up to the present time has been rapid. Television requires pictures to be sent by means of electricity. Pictures are made up of light and darkness. We should have some device which will change light into electricity, so that we can send it over wires or by radio. A number of different devices will do this for us, one of them being the photoelectric cell.

3. The photoelectric cell is a special kind of electronic tube in which light will cause an electric to flow. If there is no light, there will be no current, but when there is light on the photoelectric cell, the current will increase as the light is made brighter. Even with a very bright light the amount of current is exceedingly small but that does not matter because we can amplify the current of the photoelectric cell and obtain as much current as we require. If we amplify the current sufficiently, we can cause it to light an electric lamp and make the lamp's light proportional to that shining on the photoelectric cell.

4. It seems natural to consider sending sections of the picture, one after the other, natural because we do this ourselves when we read. If we look at a page in a book, we get no meaning from it until we start to scan it one word at a time along the line of print. As our eyes move, we see words appear one after the other until we read the end of the line when our vision jumps quickly to the line below. When we have reached the last line of the page, we start again at the top of the next page. In this way we have scanned the pages line by line.

5. The same method can be used for pictures to be sent by electricity. The sensitive spot of the photoelectric cell can be moved across the field of the picture, one spot at a time, line by line until the whole picture has been covered. If the reproducing lamp is moved in the same way, the picture will be built up, one spot at a time and line by line. The fundamental method of transmitting pictures by television, therefore, consists in analyzing the picture into elements, sending their equivalent light values by electrical means, reconverting them into light elements and reassembling the picture again. The whole process must be carried out so rapidly that the eye sees a continuous picture.

6. In television broadcasting, the sound signal is transmitted simultaneously with the video signal. The audio signal from a microphone is amplified and used to modulate the frequency sound channel carrier. Both transmitters feed one common aerial through a special coupling filter. The receiver aerial picks up the sound and vision radio frequency signals. After amplification, the sound signal is separated from the composite signal, amplified, and used to drive a loudspeaker.

7. In 1928 television in colour was first demonstrated, taking advantage of the fact that red, green and blue are primary colours from which every visual colour can be built up by combination. At present, colour TV is being widely applied. The future certainly belongs to colour liquid crystals TV, to plasma TV.

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