2020-05-11
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Radio communication is the transfer of high-frequency energy from the transmitter to the receiver. Accordingly, the main components of radio communication of any kind are a transmitter and a receiver.
The function of a transmitter is to generate electrical oscillations at radio frequency, which is called the carrier frequency. The main components of a transmitter are an oscillator, amplifiers, and a transducer.
Other important components of radio transmitters are the modulator and the aerial. As for the modulators, they use proportional voltages for controlling the variations of oscillation intensity. And the aerial is that part of a radio system from which energy is transmitted into or received from the space (or the atmosphere).
Most modern radio receivers are of super heterodyne type. In them an oscillator generates a radio-frequency wave that is mixed with the incoming signal. As a result, a radio-frequency wave of lower frequency (called intermediate frequency) is being produced. In order to tune the receiver to different frequencies, the frequency of oscillations changes but the intermediate frequency always remains the same.
А good radio receiver should have high selectivity, high sensitivity and fidelity and low noise. Selectivity is achieved by a receiver receiving signals from one station and rejecting them from another station operating on a nearby frequency. A high-fidelity receiver contains both the tuner and amplifier circuits of a radio. And the high-fidelity radio may consist of a separate audio-amplifier and a separate radio tuner.
Telephony is the transmitting of sounds over a considerable distance by means of electric current, using wires. Telephony as a means of communication is widely used in modem life all over the world. By means of a telephone apparatus people can communicate with each other at distances of thousands of kilometers. In order to carry on communication, the frequency of the transmitted oscillations should be constant during the whole period of communication. The circuit, which is closed when the line is connected, consists of a transmitter and a receiver connected by an electric conductor.
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A telephone transmitter is usually a carbon microphone. Its main parts are microphone housing, carbon chamber, carbon diaphragm, carbon granules, insulating spacer, and conductor.
Unit 4. Radio transmitter
Active Vocabulary
achievement достижение
to amplify усиливать
application применение
broadcasting радиовещание
communication передача, сообщение;
связь component компонент; элемент
to convert превращать, преобразовывать
current (электрический) ток
to develop развивать; разрабатывать
direction направление
to employ употреблять, использовать
engineering техника; инженерное искусство
frequency частота
ground заземление
oscillator генератор
to produce производить; вырабатывать
to radiate излучать
to set up восстанавливать
similar сходный; подобный
transfer перенос; передача
to transmit передавать
transmitter передатчик
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wave волна
I. Read and translated the text
Radio-Transmission
Radio is one of the greatest achievements of modern engineering. Radio employs electrical energy to transmit signals. The most developed application of radio is in communication and broadcasting.
Radio communication is the transfer of high-frequency energy from the transmitter to the receiver. The necessary components of radio communication are a transmitter and a receiver. The main parts of a transmitter are a high-frequency oscillator, a ground and an antenna. When electric oscillations are produced in the antenna, it starts radiating radio waves.
These waves travel in all directions. When radio waves reach the antenna of a receiver, they set up currents in it of a similar form to those in the transmitting antenna. These currents are directed from the antenna to a radio-receiver where they are first amplified and then converted into audio frequency signals.
A radio transmitter is an electronic device which, when connected to an antenna, produces an electromagnetic signal such as in radio and television broadcasting, two way communications or radar. Heating devices, such as a microwave oven, although of similar design, are not usually called transmitters, in that they use the electromagnetic energy locally rather than transmitting it to another location.
A radio transmitter design has to meet certain requirements. These include the frequency of operation, the type of modulation, the stability and purity of the resulting signal, the efficiency of power use, and the power level required to meet the system design objectives. High-power transmitters may have additional constraints with respect to radiation safety, generation of X-rays, and protection from high voltages.
Typically a transmitter design includes generation of a carrier signal, which is normally sinusoidal, optionally one or more frequency multiplication stages, a modulator, a power amplifier, and a filter and matching network to connect to an antenna. A very simple transmitter might contain only a continuously running oscillator coupled to some antenna system. More elaborate transmitters allow better control over the modulation of the emitted signal and improve the stability of the transmitted frequency. For example, the Master Oscillator-Power Amplifier (MOPA) configuration inserts an amplifier stage between the oscillator and the antenna. This prevents changes in the loading presented by the antenna from altering the frequency of the oscillator.
II. Answer the following questions:
1. What is the most developed application of radio?
2. What is radio-communication?
3. What does radio employ to transmit signals?
4. What are the necessary components of radio-communication?
5. Under what condition does the transmitting antenna radiate radio waves?
6. In what direction do these waves travel?
7. What happens when radio waves reach the antenna of a receiver?
