45 Electrons.

The CRT is enclosed in a metal casing made from an alloy of nickel, 9 known as mu-metal. This has a very high magnetic permeability and prevents external magnetic fields from causing unwanted beam deflections.

High definition television

Tuning-in

Task 1 Carry out a survey to find out the viewing habits of your class and their ideas

on future developments in television. You may add extra questions of your own.

1. How many hours of television do you watch each week?

2. When do you watch television?

3. What sort of programmes do you watch?

4. Which television station do you watch most /least often?

5. How do you think television will change in the future?

Compare viewing habits for your class with the viewing habits of people of your own age group in the UK. Are there any differences?

United Kingdom

Age groups Television viewing (hours/mins per week)

1984 1985 1986 1987 1988

4-15 years	16:10	19:59	20:35	19:14	18:34
16-34 years	18:16	21:36	21:10	20:03	20:36
35-64 years	23:24	28:04	27:49	27:25	27:17
65 years and over	29:50	36:35	36:55	37:41	37:25
All aged 4 years and over	23:03	26:33	25:54	25:25	25:21

Task 2 Study these graphics. Note ways in which high definition television will be

different from existing sets. Compare your answers with your partner. For example:

Feature Existing High definition

no. oflines 625 1,250

For HDTV the width/height ratio of the screen has been changed from 4:3 (as in conventional TV) to 16:9, like the screens in cinemas.From corner to corner it measures 100-125 cm.

This means your viewing range will be expanded from 10° to 30°. As a result you will have a much greater sense of reality, and may feel that you are there as the action unfolds. HDTV offers you three-dimensional sound, as it uses more speakers than today's sets.

Task3

Now search this text for further differences to add to your list.

In Europe, the USA, and Japan, the race is on to produce a new generation of television sets. These new sets will be larger than today's models, possibly with 100-centimetre flat screens. Picture quality will be excellent, crisp, and without flicker, as good as those we 5 are used to seeing in the cinema. Sound quality too will be superb, thanks to digital multitrack transmissions. By the turn of the century such sets may be offering programmes in a choice of languages as they will be equipped with eight sound tracks.

In Europe, the term HDTV is used. In the USA, the more generic term 10 ATV, Advanced Television, has been adopted. The Japanese, who were the first to start work on the new technology, in 1974, called their system Hi-Vision. Whatever name is used, these new sets share certain features.

The picture is displayed using more lines per frame. This means that 15 they provide clearer, more detailed, high quality images. The picture can be displayed on large, wide screens which are flicker-free. They also provide very high quality three-dimensional sound output.

A wider range of frequencies can be used to transmit each HDTV channel. This is because they can be transmitted at high frequencies 20 which are virtually unused at present. These wide frequency ranges make it possible to transmit digital, ratherthan analogue signals. Digital processing can then be used in the receivers to provide almost perfect pictures even when the strength of the input signal is low. A computer could also be used to produce special effects.

25 Since not everyone is convinced of the need for such high quality TV systems, the move towards HDTV is likely to be very gradual. The first HDTV receivers will need to be able to process both the old and the new transmissions and, throughout the world, agreement will have to be reached on new transmission standards.

Language study Certainty

The text describes possible future developments in television. The writer is confident about some developments and less confident about others. What difference can you see between these statements?

1. By the turn of the century such sets may be offering programmes in a choice of languages.

2. Picture quality will be excellent.

3. The move towards HDTV is likely to be very gradual.

We cannot measure certainty in language with precision, but the following table provides a guide to how certain a writer is about a future development.

Certainty (%)	Verb	Adjective	Adverb
100	will	certain	certainly
85		likely	unlikely
75		probable	probably
		improbable
50	could/may	possible	possibly

Task 4 ИЗ Listen to this expert on audio systems, recorded in 1992. Note his predictions

for each format and the certainty expressions he uses. Do you share his views? Has the situation changed today? Discuss in groups.

Prediction Certainty expressions

LPs

Cassettes

MDs

CDs

Task 5 How likely are these developments in the next five years? Make statements

about each development using the certainty expressions in the table on page 110. Compare your answers. The graph on page 98 may help you with some of the statements. For example:

Most houses in your country will be cleaned by electronic robots.

I think it's unlikely that most houses in my country will be cleaned by electronic robots. It's possible that some houses will use them.

1. Vinyl records will not be made.

2. Ordinary audio cassettes will not be made.

3. Most families in your country will have CD players.

4. Most families in your country will have MD players.

5. Most families in your country will have DCC players.

6. Computers will understand and respond to your spoken language.

7. Cars will be electronically guided through cities.

8. Most teaching will be done by computers.

9 No manual labour will be done in factories in your country. 10 Most families in your country will have HDTVs.

Technical reading Television display

Task 6 Find the answers to these questions by studying the text and diagrams on the

following page.

1. What controls the movement of the spot of light across a television screen?

1. What name is given to the rapid movement of the spot back across the screen to the start of the next line?

1. How many lines are used to build up a frame in present European television systems?

2. What happens to a screen if the frame is not scanned at least forty times per second?

Television pictures

A television picture is built up gradually by moving a spot of light across and down a screen in a raster pattern (see Fig. 1).

Fig. 7

The video signal causes the brightness of the spotto vary in proportion to the intensity of light in the original image. The 5 movement of the spot across the screen is controlled by the line scan signal. Each time the spot reaches the right side of the screen, it is blanked and moved rapidly back to the left side ready to start the next line. This rapid movement back to a starting position is known as flyback. Each complete image or frame requires a minimum of 500 10 lines to give a picture of acceptable quality. The present European TV system uses 625 lines per frame.

The movement of the spot down the screen is controlled by the field scan signal. When the spot reaches the bottom of the screen, it is blanked and moved rapidly back to the top of the screen. The frame 15 must be scanned at least forty times per second to prevent the screen from flickering. The present European TV system has a frame scan rate of 50Hz.

picture brightest (white)

picture darkest (black)

- sync (blacker than black)

T he video signal contains line and field sync pulses to make sure that the TV receiver starts a new line and a new frame at the same time as 20 the TV camera (see Fig. 2).

line sync pulses (during line flyback)

. video signal

field sync pulse (during field flyback)

Fig. 2

To allow the video signal to be transmitted using a smaller range of frequencies, each frame is transmitted in two separate halves, known as fields. The first time the spot travels down the screen it displays the first field, which consists of the odd-numbered frame lines. The 25 second time the spot travels down the screen it displays the second field, which consists of the even-numbered frame lines. Combining two fields in this way is known as interlacing. Although the fields are displayed one after the other, it happens so quickly that the human eye sees them as one complete picture.

Writing Linking facts and ideas, 4

Task 7 Link each set of statements, using words or phrases of your own to make an

explanation of how a television picture is composed. Omit unnecessary words and make any other changes required.

1. A television picture is built up gradually. This is done by a moving spot.

1. The spot strikes the television screen.

The phosphor coating on the screen emits light.

The light varies in brightness according to the intensity of the original image.

3 The spot reaches the right side of the screen. The spot is blanked.

The spot is moved rapidly back to the left side in a movement called flyback.

4 The present European system sweeps the screen in a series of lines. There are 625 closely-spaced lines.

Using 625 lines ensures a good quality picture.

5. The movement across the screen is controlled by the line scan signal. The movement down the screen is controlled by the field scan signal.

5. The scan rate must be greater than 40Hz.

A lower scan rate would cause the screen to flicker.

7 Sync pulses are added to the video signal.

The sync pulses ensure that the TV camera and TV receiver start a new line and frame at the same time.

8 The build-up of the screen happens so quickly. The eye sees only a complete picture.

Task 8 Now divide your completed statements into two paragraphs. Give your text a

suitable title.

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