Television

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 sound channel and the other is 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 a 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.

Special signals are sent out by the television transmitter in addition to the picture impulses. They 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 induces in the receiving antenna are fed into the radio-frequency stage of the receiver; and the picture and sound carriers are converted by super heterodyne conversion method into two separate intermediate frequency signals. One signal corresponds to the sound carrier and the other – to the video or picture carrier, so two separate intermediate frequency amplifier channels are employed.

The sound intermediate frequency signal is demodulated by a detector. After proper amplification by the audio amplifier, the sound signal is reproduced by the loudspeaker 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 the ordinary sound receiver. The video 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.

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To house – вмещать

Band of frequencies – полоса частот

Evacuated space – разреженное пространство

Bandwidth - полоса (частот); полоса пропускания (в системах связи - разность между максимальной и минимальной частотой в заданном диапазоне)

voltages inducer – индуктор напряжения

GRAMMAR EXERCISES

I. Form Perfect Participles Active and Passive.

Model: to accept — having accepted; having been accepted

to choose, to move, to complete, to divide, to convert, to raise,to design, to investigate.

II. Define the functions of the Participle I and translate the sentences.

1. Leaving a transmitting antenna, a radio wave travels in all directions. 2. Part of signal travelling along the ground is called the.ground wave. 3. The ionosphere has tile property of bending radio waves and returning them to the ground. 4. Bending radio waves changes the direction of the wave. 5. Obtaining new data on the waves travelling was necessary for future investigations. 6. Without using superconducting materials it was impossible to perfect this system operation. 7. Building a network of transmitting stations in that region was of prime importance. 8. The transmitter operating on the low frequencies was constructed by these students. 9. The scientist’s main task was studying ionospheric conditions.

III. Name the forms of the Participle, define their functions and translate the sentences.

1. Having lost the address of her cousin's new flat, she couldn't come to see her. 2. The site having been chosen, many houses are being built there. 3 He lost his way and not knowing English he couldn't get to Capitol Hill. 4. He got to Capitopi Hill having changed a tram for a bus. 5. Asked in English transmitting he couldn't answer anything. 6. The site of the city was chosen by G. Washington and was accepted by Congress in the act of 1790, establishing the Federal District of Columbia.

IV. Define the functions of the Participle I in Passive and translate the sentences.

1. Being heated magnetized steel loses its magnetism. 2. The new measuring instrument being developed in this laboratory will be tested by that engineer. 3 The oscillations being produced in the antenna are weak. 4. New data being obtained are necessary for nature investigations. 5. Being perfected the device operated successfully under all conditions. 6. The new receiver being tested will be used in this system. 7. Being equipped with modem instruments the laboratory carried out important experiments.

V. Translate the following sentences, pay attention to the Participle II.

1. The operation of the receiving station influenced by a number of factors was discussed by engineers. 2. The generation of electricity from magnetism dealt with by-Faraday was a very important scientific discovery. 3. The work of Rutherford followed by great help for understanding many natural phenomena. 4. Gagarin's first space flight followed by many others was very important for the development astronautics. 5. Molecules of even a good insulator acted upon by: electric field produce a motion of electrons due to the field. 6. Some drawbacks of the reactor referred to in this article will be eliminated. 7. The dimensions of the body referred to in that textbook will be used in our experiment.

VI. Translate the following text in written form and define the Participle II.