Vocabulary. 2. amplification – усиление

1. aerial - антенна

2. amplification – усиление

3. band – полоса, лента; связь

4. band filter – ленточный фильтр

5. band of frequencies – полоса частот

6. evacuated space – разреженное пространство

7. house wiring – домовая проводка

8. image - изображение

9. improper accompaniment – ненадлежащее сопровождение

10. in addition to – в добавление к …

11. in. – inch – дюйм

12. proper – надлежащий

13. properties – свойства

14. screen – экран

15. similar (to) – похожий (на), подобный

16. single – единичный, один

17. size – размер

18. to accompany – сопровождать

19. to add – добавлять

20. to appear – появляться

21. to evacuate – откачивать

22. to house – вмещать

23. to pick up – принимать, улавливать

 

a) Television broadcasting is similar to radio broadcasting except that it is considerably more complex than the radio – sound broadcasting system. The cause of it is that much more signal space – that is bandwidth – is necessary to carry the complex video signal together with the audio signal.

In a typical television system two separate transmitters are employed –

one for the sound channel and the other for the picture channel. The sound transmitter is frequency modulated. It simultaneously transmits the sound and the image. The image is accompanied by the sound in the process of broadcasting and each of the transmitters is supplied with its own aerial. The image being televised is received by the television camera, which converts the optical image into electrical impulses. The camera includes an optical lens system similar to that used in a photographic camera, the image from which is projected into camera tube. The camera tube includes a photosensitive mosaic which is scanned by an electron beam. The beam, in its turn, is housed in an evacuated glass tube. Usually the output signals of the camera tube are preamplified within

the camera itself by the video or picture amplifier. After proper amplification, the video signal modulates the high – frequency carrier of the television transmitter and is radiated into space by the aerial. As for the picture carrier, it is amplitude – modulated.

 

b) Special signals are sent out by the television transmitter in addition to the picture impulses. These special signals have the purpose of synchronizing the picture at the receiver with that being picked up by the camera.

At the television receiver, the picture and audio signals are picked up simultaneously by a single antenna. The voltages induced in the receiving antenna are fed into the radio – frequency stage of the receiver; and the picture carrier and the sound carrier are converted by superheterodyne convertion method into two separate intermediate frequency signals. One signal corresponds to the sound carrier and the other – to the video or picture carrier.

Two separate intermediate frequency amplifier channels are employed, one for the picture signal and the other for the sound signal. The sound intermediate frequency signal is demodulated by a detector. After proper amplification by the audio amplifier, the sound signal is reproduced by the loud - speaker in the usual way.

The picture intermediate frequency signal is amplified by several stages having wide – band frequency characteristics and is then fed into the video (picture) detector, where the intermediate frequency signal is then demodulated in the same way as in an ordinary sound receiver. The video (picture) signal which appears in the output of the detector is then amplified in a video amplifier, which corresponds to the audio amplifier in a sound receiver, except that it must pass a much wider range of frequencies.

In place of the loud – speaker used in the sound system, a device is used which converts the varying amplitude of the video signals into corresponding variations of light.