Вопрос № 237509 - Английский язык

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Radio Systems
1. Radio systems used for communications will have the following elements. With more than 100 years of development, each process is implemented by a wide range of methods, specialized for different communications purposes. Each system contains a transmitter. This consists of a source of electrical energy, producing alternating current of a desired frequency of oscillation. The transmitter contains a system to modulate some property of the energy produced to impress a signal on it.
2. This modulation might be as simple as turning the energy on and off, or altering more subtle properties such as amplitude, frequency, phase, or combinations of these properties. The transmitter sends the modulated electrical energy to a tuned resonant antenna; this structure converts the rapidly changing alternating current into an electromagnetic wave that can move through free space.
3. The electromagnetic wave is intercepted by a tuned receiving antenna; this structure captures some of the energy of the wave and returns it to the form of oscillating electrical currents. At the receiver, these currents are demodulated, which is conversion to a usable signal form by a detector sub-system. The receiver is «tuned» to respond preferentially to the desired signals, and reject undesired signals.
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In electronics, a transistor is a semiconductor device commonly used to amplify or switch electronic signals. A transistor is made of a solid piece of some semiconductor material, with at least three terminals for connection to the external circuit. A voltage or current applied to one pair of the transistor terminals changes the current flowing through another pair of terminals. Because the controlled (output) power can be much larger than the controlling (input) power, transistors provide amplification of a signal. A transistor is a fundamental building block of modern electronic devices, and it is used in radios, telephones, computers and other electronic systems. Some transistors are packaged individually but most of them are found in integrated circuits.
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