Материал: Практикум по грамматике, чтению и переводу с английского языка Новосибирск 2008 Оглавление

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Analogue television basics

Television is the transmission and reception of pictures and sound by very high frequency (VHF) radio waves. In the television studio, or during outdoor broadcasts, one or more television cameras produce electrical signals of a moving visible scene. A video amplifier amplifies these signals and sends them along a line to the transmitting station. At the same time, sounds associated with the scene are converted into electrical signals by a microphone and these, too, are amplified along with the video signal. At the television transmitting station, two carrier waves are modulated, one with the video information and one with the sound information. The transmitting aerial picks up this wave and amplifies it before demodulating the vision and sound components. Two signals are separated out. The demodulated sound signal passes to an AF amplifier before being passed to a loudspeaker that recreates the original sound as accurately as possible. A video amplifier amplifiers the demodulated video signal before being passed to a cathode ray tube in the TV receiver to recreate an image of the original scene. A black-and-white television camera combines optics and electronics to produce electronic signals. The basis of this camera is the vidicon tube. It produces a narrow beam of electrons aimed at a photosensitive material on which a lens system focuses an optical image. I front of the target is a transparent aluminium film. The variation in brightness of the image is “read” using an electron beam that is made to move back and forth over the target. During this scanning process, the electron current varies in the circuit comprising the electron beam, the target, resistor, the power supply and the electron gun. The strength of the electron current thus follows the brightness of the image, and resistor turns these current variations into voltage variations comprising video signal. In the vidicon tube, the electron beam is made to scan the target by suitable signals passing through the scanning coils wound round the tube. The spot of electrons is first positioned at the top of the target and rapidly moved horizontally. At the end of the line, the spot is moved rapidly back to the left side of the target. This very rapid return of the spot is called flyback. A second line is now traced and the process repeated until the spot has reached the bottom right-hand corner of the target. The spot is then returned to the top left-hand corner of the screen and a second picture traced out. Thus scanning produces a picture made up of a set of parallel lines called a raster. The system that deflects the spot horizontally is called the field scan, and that which moves the spot downwards at a much slower rate is called line scan. The deflection is produced by magnetic fields generated by currents having a sawtooth shape. Scanning is a common way of building up pictures and is used in the cameras on weather satellites, and on interplanetary spacecraft that send us detailed pictures of planets during their exploration of the Solar System. In a TV receiver the picture is displayed on the screen of a cathode ray tube (CRT). The tube is an airless glass envelope, narrow and cylindrical at one end and flared out at the other end to form a viewing screen. By heating a filament at the narrow end, electrons are produced and these are accelerated and focused into a narrow beam by an electron gun before being “fired” along the axis of the tube towards the positive anodes. The horizontal and vertical deflection coils clamped round the neck of the tube move the beam back and forth across the screen to build up a picture as a set of lines on the screen. Where the electrons strike the phosphor, light is produced, the brightness of which is determined by the energy of the electrons. External controls on the receiver enable the intensity of the electron beam and therefore the overall brightness of the screen to be adjusted. Because a TV picture contains a lot of information, TV needs a bandwidth of about 11 MHz. In order to save “radio space”, this rather large bandwidth is halved to 5.5 MHz by a technique called interlaces scanning. Each complete picture is divided into two frames that are scanned and transmitted one after the other and then reassembled at the TV receiver. Thus, after the beam has scanned half the picture comprising 312.5 lines in 1/50s, it returns to scan the intervening lines. Therefore, although 50 frames are transmitted per second, only 25 complete pictures are transmitted per second.


Vocabulary:

to radiate – излучать

vidicon tube – видикон

electron gun – электронный прожектор, электронная пушка

scanning coil – отклоняющаяся катушка

AF - audio frequency – звуковая частота

scanning – обследование, развертка изображения

flyback – обратный ход луча

raster – растр

to deflect – отклонять

field scan – полевая развертка

line scan – строчная развертка

glass envelope – стеклянная колба, баллон

flared – расширяющийся, расширенный на конус

to clamp – зажимать, фиксировать

bandwidth – ширина полосы часто, полоса частот

interlaced scanning – черезстрочная разверстка

intervening lines – промежуточные линии

XIV. Find Gerunds in the text and define their functions.

XV. Read the text again and answer the questions.


  1. What is television?

  2. What is the role of transmitting and receiving aerials in television?

  3. What is the basis of black-and-white television camera?

  4. Describe the principle of a vidicon tube.

  5. Where is process of scanning used?

  6. Describe the principle of a cathode ray tube in a TV receiver.

  7. Why does TV need a bandwidth of about 11 MHz?

  8. What is an interlaced scanning? What is it used for?



XVI. Combine words from Box A with words from Box B to make collocations.

A

broadcast

transmitting

photosensitive

electron

scanning

glass

intervening

electron

B

gun

system

lines

coil

station

envelope

beam

material

XVII. Connect the words with their definitions.

  1. flyback 6. interlaced scanning

  2. television 7. deflection

  3. electron gun 8. aerial

  4. raster 9. demodulation

  5. bandwidth 10. broadcast

  1. the act or process by which an output wave or signal is obtained having the characteristics of the original modulating wave or signal;

  2. a pattern of horizontal scanning lines traced by an electron beam, especially on a television screen;

  3. the fast return of the spot on a cathode-ray tube after completion of each trace;

  4. a transmission of a program on radio or television;

  5. the range of frequencies within a given waveband used for a particular transmission;

  6. the part of a radio or television system having any of various shapes, such as a dipole, long-wire, or vertical aerial, by means of which radio waves are transmitted or received;

  7. a system of scanning a television picture, first along even-numbered lines, then along the odd-numbered lines, in a complete scan;

  8. the system or process of producing on a distant screen a series of transient visible images, usually with an accompanying sound signal;

  9. the change in direction of a light beam as it crosses a boundary between two media with different refractive indexes;

  10. a heated cathode with an associated system of electrodes and coils for producing and focusing a beam of electrons, used especially in cathode-ray tubes.


XVIII. Complete each sentence with a word from the box.


Flyback, vidicon tube, deflection soils, television, scanning, electron gun, bandwidth, aerial, electron beam, microphone
  1. 1   ...   22   23   24   25   26   27   28   29   ...   36

The purpose of the …………….. is to convert the sound pressures into electrical impulses of varying amplitude.

  • The electron beam that scans the picture in the ……………… must be in exactly the same position at all times as the electron beam that scans the screen in the picture tube.

  • The vision signal contains only half the picture information thereby reducing the ………………. by half to 5.5 MHz.

  • Both line and frame synchronizing pulses are added back to the video signal during the …………….. when the line is blanked out.

  • …………….are conventionally divided into transmitting and receiving, though in most cases there is no principle difference between them.

  • A kinescope is a large vacuum tube used for ……………… and viewing the transmitted pictures.

  • When colour ………………. was introduced in the UK in 1967, consideration had to be given to owners of monochrome receivers so that they could continue to receive a normal monochrome picture.

  • In the television system devised by Vladimir K. Zmorykin a narrow …………….. is used to scan the image in a photoelectric tube of special design called an iconoscope.

  • The electron beam is produced by an ………………. , which consists of a heated cathode, a grid and the anodes.

  • All three electron guns scan the screen under the control of the same ……………… .

    XIX. Translate the sentences, paying attention to the meanings of highlighted words

    1. Setting targets is very important when you want to achieve something. 2. He has become the target for a lot of criticism recently. 3. The campaign is clearly targeted on the young. 4. She scanned the advertisement pages of the newspaper over breakfast. 5. I scanned the book for every detail of the transistor operation. 6. Text and pictures can be scanned into the computer. 7. The camera tubes are scanned in synchronism using internal electron beams that produce three separate voltages, representing the 8 MHz colour information. 8. Suppose the picture being scanned has n elements. 9. Luckily I managed to get home half an hour before the first spots of rain started to fall. 10. His jacket was covered with spots of mud. 11. The process of scanning consists of moving an exploring element or spot over the image to be transmitted in a periodically repeated path covering the entire image area.

    XX. Change the sentences, using the words in brackets according to the model.

    Model: The attendants don’t permit the taking of photographs. (visitors)

    The attendants don’t permit visitors to take photographs.

    1. The engineer advised using a variable capacitor to tune different stations in. (their colleges)

    2. The teacher recommends recalling the material about audio amplifier. (the student)

    3. The necessity to save “radio space” doesn’t permit increasing of bandwidth. (radio station)

    4. The professor intends using amplitude modulation to transmit the bandwidth. (the engineer)

    5. A new communication satellite allowed using regular Hi-Vision service. (tiny aerials)

    XXI. Discussion. In pairs discuss the following questions.

    1. Speak about different types of television, their advantages and disadvantages. (cable television, colour television, digital television, high-definition television).

    2. Paraphrase the following quotation. Express your opinion about it.

    • Источник: https://files.student-it.ru/previewfile/256648

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