无线电接收机英文资料及中文翻译

1 英文资料及中文翻译

Radio Receiver

A block diagram for a modern radio receiver is shown in Fig..2-4.The input signals to

this radio are amplitude-modulated radio waves. The basic electronic circuits include:

antenna ,tuner, mixer, local oscillator ,IF amplifier, audio detector, AF amplifier,

loudspeaker, and power supply.

Fig.2-4 A Block Diagram For Modern Radio Receiver

Any antenna system capable of radiating electrical energy is also able to abstract

energy from a passing radio wave. Since every wave passing the receiving antenna.

Induces its own voltage in the antenna conductor, it is necessary that the receiving

equipment be capable of separating the desired signal from the unwanted signals that are

also inducing voltages in the antenna. This separation is made on the basis of the difference

in frequency between transmitting stations and is carried out by the use of resonant circuits,

which can be made to discriminate very strongly in favor of a particular frequency. It has

already been pointed that, by making antenna circuit resonant to a particular frequency, the

energy abstracted from radio waves of that frequency will be much greater than the energy

from waves of other frequencies; this alone gives a certain amount of separation between

signals. Still greater selective action can be obtained by the use of additional suitably

adjusted resonant circuits located somewhere in the receiver in such a way as to reject all

but the desired signal. The ability to discriminate between radio waves of different

frequencies is called selectivity and the process of adjusting circuits to resonance with the

frequency of a desired signal is spoken of as tuning.

Although intelligible radio signals have been received from the stations thousands of

miles distant, using only the energy abstracted from the radio wave by the receiving

antenna much more satisfactory reception can be obtained if the received energy is 2 amplified. This amplification may be applied to the radio-frequency currents before

detection, in which case it is called radio-frequency amplification or it may be applied to

the rectified currents after detection, in which case it is called audio-frequency

amplification. The use of amplification makes possible the satisfactory reception of signals

from waves that would otherwise be too weak to give an audible response.

The process by which the signal being transmitted is reproduced from the

radio-frequency currents present at the receiver is called detection, or sometimes

demodulation. Where the intelligence is transmitted by varying the amplitude of the

radiated wave, detection is accomplished by rectifying the radio frequency current. The

rectified current thus produced varies in accordance with the signal originally modulated

on the wave irradiated at the transmitter and so reproduces the desired signal. Thus, when

the modulated wave is rectified, the resulting current is seen to have an average value that

varies in accordance with the amplitude of the original signal.

Receiver circuit are made up a of a number of stages. A stage is a single transistor

connected to components which provide operating voltages and currents and also signal

voltages and currents. Each stage has its input circuit from which the signal comes in and

its output circuit from which the signal, usually amplified, goes out. When one stage

follows another, the output circuit of the first feeds the signal to the second. And so the

signal is amplified, stage by stage, until it strong enough to operate the loudspeaker.

Radio Waves

Radio Waves are a member of the electromagnetic of waves. They are energy-carriers

which travel at the speed of light (ν), their frequency(ƒ) and wavelength(λ) being related ,

as for any wave motion, by the equation

ν=ƒ* λ

where ν=c=3.0*108 m/s in a vacuum (or air). If λ=300m, then ƒ=ν/λ=3.0*108

/(3.0*10 2)=106Hz=1MHz. The smaller λ is, the larger ƒ.

Radio Waves can be described either by their frequency or their wavelength. But

the former is more fundamental since, unlike λ (and ν ), f does not change when the waves

travel form one medium to another.

Radio Waves can travel form a transmitting aerial in one or more of three different

ways.

Surface or ground wave.. This travels along a ground, the curvature of the earth’s

surface. Its range is limited mainly by the extent to which energy is absorbed form it by the

ground. Poor conductors such as sand absorb more strongly that water, and the higher the