无线电接收机

中文译文
无线电接收机(中文3500字,英文2700字)
任何天线系统既能辐射无线电波又能接收无线电波。任何经过天线的无线电波均能在天线中感应电压，因此，接收机必须能够从天线所收到的所有信号中分离出有用信号。这个分离过程是根据发射端发射的信号频率不同，利用调谐回路完成的。调谐回路能够有效地从众多频率中选择出某一个特定频率。通过天线调谐回路对某一特定频率地谐振，可以使天线从这一特定频率中吸收的能量比从其他平频率中吸收的能量大得多，这样，就从某种程度上实现了信号的分离。进一步的选择作用可以通过接收机中的某些经过适当调谐的谐振回路实现，以这种方式进一步去除了有用信号以外的其他信号。将不同频率的无线电波加以区别的能力称为选频，将谐振回路的频率调在有用信号频率上的过程称为调谐。

英文原文
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.
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.