自动化1 08928129 吴天乐 老师：应南娇

Lesson18

Radio Receiver

The purpose of a receiver is to select a desired group of frequencies coming from one transmitter, get rid of all unwanted signals and noises, and then demodulate the signal to obtain the modulating information. The better the receiver does its job, the closer the demodulated signal will resemble the original signal coming from the transmitter. Regardless of the type of demodulation required, the main functions performed by a receiver are filtering and amplifying. Practically all receivers in use today are of the superheterodyne configuration. Figure 18-1 is a block diagram of a typical superheterodyne receiver.

接收器的目的是要从一个发射器中选出一个预期的群频率,除去所有的无用信号和噪声,然后解调信号来获得调制的信息。接收器工作地越好，解调的信号与来自传输器原信号的相似度就越接近。无论哪类解调要求、其主要功能都是通过放大过滤和接收器进行的。实际上，现在使用的所有接收器都是超外差式收音机的配置。图18-1是一个典型的超外差配置接收机框图。

The incoming signal is amplified with a single stage of tuned RF amplification, then mixed with an adjustable local oscillator(LO)to produce a signal at a fixed intermediate frequency(IF), in this case it is 465 kHz. From then on the receiver consists of a set of fixed-tuned IF amplifiers, including selective elements such as crystal or mechanical filters, finally terminating in detector and a audio amplifier.

一个进入的信号通过一个单级无线频率调整放大,然后与可调节的本地振荡器混合，再产生一个固定的中频信号。在这个例子中,它的频率是4.65千赫兹。从那时起,接收器由一套固定调整中频放大器组成,包括选择性元素如晶体或机械过滤器、最后终止于检测器和音频功率放大器。

Changing the LO frequency tunes the receiver since a different input frequency then gets mixed to the IF passband frequency. The input RF amplifier must be gang-tuned with the local oscillator. Its purposes are to improve the sensitivity with a stage of low amplification prior to mixing and to reject signal at the "image " frequency , in the case input signals are at a frequency of 465 kHz above the LO (a mixer generates sum and different frequencies). In other words, the superheterodnye receiver uses a mixer and local oscillator to shift the frequency of a signal to the input frequency at which most of gain and selectivity are concentrated.

从不同的输入频率改变本地振荡器的频率调整接收器并混合中频通频带频率。输入射频放大器必须被本地振荡器成群调整。它的目的是提高混合前低阶放大信号的灵敏度和拒绝图象信号频率,如在输入信号的频率是4.65千赫的本地振荡器(一个混合器产生总量和不同的频率)。换句话说, 超外差的接收机使用高速混合机及本地振荡把信号频率移动到那个大部分增加和选择性集中的输入频率段

Detector separates the audio part from the signal and the then the audio frequency amplifier amplifies the audio signal to make it strong enough to drive the loudspeaker. The recovered audio level will determine the amount of gain required in the following audio amplifiers.

探测器从信号中分离出音频部分然后音频放大器放大声音信号使它增强到足以推动扬声器。之后回收的音频等级将决定在接下来的音频功放需要的增益量。

全文翻译：

收音机

接收器的目的是要从一个发射器中选出一个预期的群频率,除去所有的无用信号和噪声,然后解调信号来获得调制的信息。接收器工作地越好，解调的信号与来自传输器原信号的相似度就越接近。无论哪类解调要求、其主要功能都是通过放大过滤和接收器进行的。实际上，现在使用的所有接收器都是超外差式收音机的配置。图18-1是一个典型的超外差配置接收机框图。

一个进入的信号通过一个单级无线频率调整放大,然后与可调节的本地振荡器混合，再产生一个固定的中频信号。在这个例子中,它的频率是4.65千赫兹。从那时起,接收器由一套固定调整中频放大器组成,包括选择性元素如晶体或机械过滤器、最后终止于检测器和音频功率放大器。

从不同的输入频率改变本地振荡器的频率调整接收器并混合中频通频带频率。输入射频放大器必须被本地振荡器成群调整。它的目的是提高混合前低阶放大信号的灵敏度和拒绝图象信号频率,如在输入信号的频率是4.65千赫的本地振荡器(一个混合器产生总量和不同的频率)。换句话说, 超外差的接收机使用高速混合机及本地振荡把信号频率移动到那个大部分增加和选择性集中的输入频率段

探测器从信号中分离出音频部分然后音频放大器放大声音信号使它增强到足以推动扬声器。之后回收的音频等级将决定在接下来的音频功放需要的增益量。