Unit IV Frequency converters

EXERCISE EXERCISE EXERCISE EXERCISE EXERCISE 1EXERCISE EXERCISE

Before reading the text answer questions:

• What branch of technology are frequency converters connected to?

• What role do they play?

• In what devices are they used?

EXERCISE 2EXERCISE EXERCISE

Read and translate the international words:

Apparatus, system, channel, amplitude, modulation, unit, generators, electric filter, differential, limiter, compressors, correction, terminal, element, diode, transistor, transfer, spectrum, area, heterodyne, detector, receiver, conversion, process, principle of modulation, periodically, characteristics, radio, integrated, ordinary, balanced, crystal, professional, decameter, bipolar, unipolar, isolation, type.

EXERCISE 3

Find the Russian equivalents to the following words and word combinations in the box

Multichannel system, frequency division of channels, amplitude modulation, a number of various devices, frequency converter, amplifier, differential system, amplitude limiter, electric filter, correction circuit, frequency spectrum, super heterodyne detector, intermediate frequency, diode, super high frequency, low noises, bipolar transistor, unipolar transistor, non-balanced converter, double balanced converter.

Амплитудная модуляция, многоканальная система, преобразователь частоты, ограничитель амплитуд, множество различных устройств, биполярный транзистор, полевой транзистор, частотное разделение каналов, усилитель, промежуточная частота, СВЧ, выравнивающий контур, спектр частот, супергетеродинный приемник, электрический фильтр, диод, дифференциальная система, малые шумы, двойной балансный преобразователь, небалансный преобразователь.

EXERCISE 4

Read and translate the text using words and word combinations.

Words and word combinations to be remembered:

Thin-route systems – малоканальная система

unit – узел аппаратуры

transceiving devices – устройство приема и передачи сигналов

range extenders – сжиматель диапазона

range compressors –ограничитель диапазона

delineation circuits – выравнивающий контур

terminal units – оконечная аппаратура

nonlinear elements - нелинейные элементы

dead – пассивный

semiconductor –полупроводник

amplification – усиление

frequency spectrum transfer – перенос спектра частот

upwards / downwards – вверх/ вниз

fluctuation-carrier frequency – частота несущего колебания

at the output of the converter – на выходе преобразователя

line circuits with periodically changing characteristics – линейные цепи с периодически меняющимися параметрами

integrated – интегральный

ordinary – простой

balanced - балансный

ring – кольцевой

unipolar –полевой

circuit isolation – развязка между цепями

Frequency converters

Apparatuses on multichannel and thin-route systems with frequency division of channels and amplitude modulation are comprised into a number of various devices commonly called units. Main units of a multichannel system with frequency division of channels and amplitude modulation are frequency converters, amplifiers, generators, electric filters and several special units – differential systems, transceiving devices, amplitude limiters, range extenders and range compressors, delineation circuits and correction circuits.

Frequency converters are one of the most important terminal units because they are the very devices to create multichannel systems with frequency division of channels and amplitude modulation. For this purpose in the converters there are used nonlinear elements: dead (semiconductor diodes) and active (transistors). There are also used frequency converters with electron tubes which help to obtain greater signal amplification.

Frequency converters are used to transfer frequency spectrum from one area into another. They are part of super heterodyne detector (a frequency converting receiver). The result of conversion is a new frequency value f called intermediate value. The intermediate frequency can be both higher and lower than signal frequency. In the first case the frequency conversion is upwards, in the other case it is downwards. In this process the frequency conversion principle of modulation is not broken, only fluctuation-carrier frequency is changed at the output of the converter.

To convert frequency there are used line circuits with periodically changing characteristics in radio receivers. The structural circuit consists of a converting element, heterodyne and filter. According to the type of a converting element the frequency converters are usually divided into diode, transistor and integrated converters. There is a different number of converting elements, so one can find the following types of converters: ordinary (with one converting element), balanced (two elements), and ring (4 elements).

Most SHF (super high frequency) receivers use crystal diodes as converting element. Crystals have fast response and comparatively low noises. But they have a drawback - they don’t have amplifying properties. Such converters are used in professional devices of decameter range.

Transistor converters use bipolar transistor, or unipolar transistor as converting element. Balanced converters are combination of two non-balanced converters. To increase channel isolation between a signal and a heterodyne there are used double balanced converters called ring converters. Such type converters have low noises and better amplitude characteristics. They are used in frequency range up to 100 MHz in professional decameter devices.

EXERCISE 5

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 6

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 7

Fill in the gaps using proper words from the text

1. Apparatuses on ______and thin-route systems with frequency division of channels and amplitude modulation are comprised into different_____.

2. 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.

3. There are also used frequency converters with ______ which help to obtain greater signal amplification.

4. Frequency converters are used ______ frequency spectrum from one area into another.

5. In this process the frequency _______ is not broken, only _______ is changed at the output of the converter.

6. The structural circuit consists of a converting element, ______ and filter.

7. One can find the following types of converters: _____ (with one converting element), ______ (two elements), and _____ (4 elements).

8. Most SHF receivers use ______ as converting element.

9. Transistor converters use _____ transistor or ______ transistor as converting element.

EXERCISE 8

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.

EXERCISE 9

Read and translate the text “AM broadcast radio and FM broadcast radio”. Use the dictionary if you need