Receiver
Переведите сочетания rejected design_____________________________________ achieved purposes _________________________________ noisy system________________________________________ intermediate frequency ______________________________ low selectivity _______________________________________ stages of amplification
Прочитайте и переведите следующие вопросы, найдите ответы в тексте • What device in a receiver generates a radio-frequency wave? • What signal does a radio-frequency wave mix with? • Does the intermediate frequency change or does it remain the same? • By what means is the aerial circuit tuned? • What are the main characteristics of a good receiver? • By what means is high sensitivity of the receiver achieved?
Most modern radio receivers are of superheterodyne 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. The oscillator is tuned by changing the capacity of the capacitor in its tuned circuit. The aerial circuit is also tuned by a capacitor in its tuned circuit. What are the characteristics of a good radio receiver? They are as follows. A 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. High sensitivity is achieved by having numerous stages of amplification. But it should be noted that high amplification is useful only if high fidelity of the system is achieved. It is also important to achieve as low noise as possible. The most sensitive receivers have one stage of tuned radio-frequency amplification.
Aerial
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