Английский язык в сфере компьютерных и телекоммуникационных технологий (стр. 13 )

unipolar –полевой

circuit isolation – развязкамеждуцепями

EXERCISE 6

Scan the text again and count how many times the words ‘converter’ and ‘amplitude modulation’ are used in different combinations. Also give 5 verbs, 5 adverbs and 5 nouns concerning the subject of the text. What verb is met in the text most often? In what voice?

EXERCISE 7

Answer the questions about the text:

1. What units can be called the main units of a multichannel system?

2. Which elements are used in frequency converters?

3. Which other elements, beside non-linear are enabled in communication apparatuses? What is their advantage?

4. Why do radio engineers need frequency converters?

5. What is changed with the help of the frequency converters?

6. What elements does the circuit of a FC (frequency converter) consist of?

7. What types of FC can you name?

EXERCISE 8

Fill in the gaps using proper words from the text.

Apparatuses on ______and thin-route systems with frequency division of channels and amplitude modulation are comprised into different_____. Main units of a multichannel system are ______, amplifiers, generators, electric filters and several special units – differential systems, _______, amplitude limiters, range extenders and range compressors, _______ and correction circuits. There are also used frequency converters with ______ which help to obtain greater signal amplification. Frequency converters are used ______ frequency spectrum from one area into another. In this process the frequency _______ is not broken, only _______ is changed at the output of the converter. The structural circuit consists of a converting element, ______ and filter. One can find the following types of converters: _____ (with one converting element), ______ (two elements), and _____ (4 elements). Most SHF receivers use ______ as converting element. Transistor converters use _____ transistor or ______ transistor as converting element.

EXERCISE 9

Translate sentences into Russian.

1.К основным узлам аппаратуры многоканальных систем с частотным разделением сигналов и амплитудной модуляцией относятся преобразователи частоты, усилители, генераторы, электрические фильтры.

2. Помимо основных узлов аппаратуры, существует ряд специальных узлов – дифференциальные системы, устройства передачи и приема сигналов, ограничители больших амплитуд, сжиматели и расширители диапазона, выравнивающие и корректирующие контуры.

3.Преобразователи частоты являются одним из важнейших узлов оконечной аппаратуры, поскольку только с их помощью возможно построение многоканальных систем с частотным разделением сигналов и амплитудной модуляцией.

4.При преобразовании частоты закон модуляции не нарушается, а изменяется только частота несущего колебания на выходе преобразователя.

5.В зависимости от вида преобразовательного элемента преобразователи частоты подразделяются на диодные, транзисторные, интегральные.

6.В зависимости от количества преобразовательных элементов выделяются следующие виды преобразователей: простые (один ПЭ), балансные (2 ПЭ), кольцевые (4 ПЭ).

7.Кристаллические диоды обладают малой инерционностью и сравнительно малыми шумами.

8.В транзисторных преобразователях частоты используют биполярный или полевой транзистор.

Text II

AM and FM broadcast radio

EXERCISE 1

Read and translate the text. Use the dictionary if you need.

AM broadcast radio sends music and voice in the Medium Frequency (MF—0.300 MHz to 3 MHz) radio spectrum. AM radio uses amplitude modulation, in which the amplitude of the transmitted signal is made proportional to the sound amplitude captured (transduced) by the microphone while the transmitted frequency remains unchanged. Transmissions are affected by static and interference because lightning and other sources of radio that are transmitting at the same frequency add their amplitudes to the original transmitted amplitude.

FM broadcast radio sends music and voice with higher fidelity than AM radio. In frequency modulation, amplitude variation at the microphone cause the transmitter frequency to fluctuate. Because the audio signal modulates the frequency and not the amplitude, an FM signal is not subject to static and interference in the same way as AM signals. FM is transmitted in the Very High Frequency (VHF—30 MHz to 300 MHz) radio spectrum. VHF radio waves act more like light, travelling in straight lines, hence the reception range is generally limited to about 50-100 miles. During unusual upper atmospheric conditions, FM signals are occasionally reflected back towards the Earth by the ionosphere, resulting in Long distance FM reception. FM receivers are subject to the capture effect, which causes the radio to only receive the strongest signal when multiple signals appear on the same frequency. FM receivers are relatively immune to lightning and spark interference.

FM subcarrier services are secondary signals transmitted "piggyback" along with the main program. Special receivers are required to utilize these services. Analog channels may contain alternative programming, such as reading services for the blind, background music or stereo sound signals. In some extremely crowded metropolitan areas, the subchannel program might be an alternate foreign language radio program for various ethnic bcarriers can also transmit digital data, such as station identification, the current song's name, web addresses, or stock quotes. In some countries, FM radios automatically retune themselves to the same channel in a different district by using sub-bands.

EXERCISE 2

Make up questions to the answers below

1.Q:______________________ ?

A: MF—0.300 MHz to 3 MHz

2.Q:__How ________amplitude and ________change?

A: The amplitude of the transmitted signal is made proportional to the sound amplitude captured (transduced) by the microphone while the transmitted frequency remains unchanged.

3.Q: What_________________affected ___?

A: Transmissions are affected by static and interference.

4.Q: ___________________________?

A: AM is transmitted in the Medium Frequency but FM is transmitted in the Very High Frequency

5.Q:____________________________?

A: 30 MHz to 300 MHz.

6. Q:___________________________?

A: to lightning and spark interference.

7.Q:___________________________?

A: They are secondary signals transmitted "piggyback" along with the main program.

EXERCISE 3

Work in pairs. Choose between  the topics ‘AM broadcast radio’ and ‘FM broadcast radio’. Exchange information addressing to your partner, ask questions and get answers.

UNIT VI

AMPLIFIERS

Text I

What do we call Amplifiers

EXERCISE 1

Practice saying some words from this unit and put them in the right stress pattern box.

Terminal	Heterodyne	Demodulator	Fluctuation
apparatus	Relation	Therefore	Output
Intermediate	compression	Amplitude	Professional
frequency	controlling	transceiving	decameter

EXERCISE2

Work with the partner. Take it in turns to dictate abbreviations and write them down. Can you decode all of them?

IBM, IT, VHF, MHz, INMARSAT, UNIX, DOS, NT, OS, AM, FM, PC, NC, GPRS.

EXERCISE 3

Choose the word that doesn’t suit in each group

Transformer, transistor, transabdominal, transfer, transceiver Radiation, fluctuation, modulation, meditation, acceleration Antenna, currant, radio wave, signal, Hertz Spectrum, apparatus, diagram, decameter, publicity Obsolete, modern, up-to-date, latest, experimental Converter, energizer, detector, amplifier, receiver, motor Trim, inclination, elevation, depression, deviation, Periodically, technically, visually, structurally, mechanically Focused, coherent, duplex, terminal, aperiodic

EXERCISE 4

Read the text and be ready to answer the questions after the text.

Amplifiers are essential units of terminal and intermediate apparatuses in multichannel systems. Amplifiers used in radio communication are divided into individual, generic and single-component signal amplifiers.

Individual amplifiers are designed to intensify signals in single channels. In modern multichannel systems which are built, as a rule on, the basis of generic principle, such amplifiers are used only in individual part of a terminal apparatus, amplifiers being installed after demodulator (a signal converter), therefore, they become amplifiers of sonic frequency. In multichannel systems created on the base of individual principle, individual amplifiers are used both in terminal and in intermediate apparatuses as means of intensification of high frequency current. Duplex amplifiers are individual too.

Generic amplifiers are used to intensify signals in channel banks. They are used both in batches of terminal apparatuses and in intermediate apparatuses of multichannel systems built on the base of batch principle. Both batch and individual amplifiers are used to intensify multichannel signals; hence, they should be aperiodic.

In addition to individual and batch amplifiers, in apparatuses of multichannel systems there are amplifiers which intensify the carrier current and currents of different controlling signals – pilot frequencies, telecontrol signals, and selection and calling signals. These signals are mostly fixed-frequency (sine) signals. Resonance amplifiers are used to intensify them.

Signal amplification can be provided either in frequency without its conversion or with conversion of frequency. Receiver intensifying radio frequency is called straight amplifier: receiver converting frequency in radiotrackt is called superheterodyne. Frequency amplifiers provide frequency intensification and its subsequent noise filtering.

Main electric properties of multichannel systems amplifiers are: gain factor or intensifying possibility of an amplifier and its frequency relation; input and output resistance of an amplifier; output power of an amplifier; gain compression appearing in amplifier; amplifier noises.