1、Modern civil and military facilities using electronic equipment is various, electromagnetic environment complex, mutual interference serious. Generally, cars, boats and planes of the communication equipment to send and receive machines were integrated together. To shortwave communication equipment,
2、for example, the remnants of the signal transmitter in receiver input from the level of 120 dB V (i.e. 13 dBm) or higher. And for the weak signal receiver receive level may only-6 0 dB V (namely-117- 113 dBm). So,the signal processing requirements receiver dynamic range as high as 120 to 126 dB. I a
3、ddition, high level and jamming signal reception frequency signal only apart dozens KHZ, so, high level jamming signal and they produced in receivers of inter modulation product will seriously affect the output of the receiver signal-to-noise ratio. In order to reduce the influence, requires the rec
4、eiver has the following characteristics: high selectivity, dynamic range as far as possible to the receiver； High linear, before in the channel filter, reduce the jamming signal with high level in the channel band pass filter of within the inter modulation products； very low this vibration phase noi
5、se, in order to avoid the interference of the adjacent signals vibration switch to the receiver channel noise in bandwidth. As an important part of the receiver receiver rf is receiver key components of the dynamic performance, it works used before amplifier. Such as dynamic range, inter modulation
6、distortion,-1 dB compression of the first three points inter modulation intercept point, and the performance of the receivers have a direct relationship. Radio is using radio waves to the recipient of the communication program broadcast voice, belong to the radio communication category. Radio statio
7、ns in order to make the voice signal out, the launch of the electromagnetic wave must with audio signal. Audio signal is through a modulator of various signal sound to be treated. Its very low frequency, such as the frequency of the voices in about 300 Hz 3000 Hz, music frequency general in frequenc
8、y 50 Hz 15000 Hz, the frequency is to pass out, must be put in the low frequency signal with high frequency electromagnetic wave, such a process called modulation, not the modulation of high frequency electromagnetic called carrier. Audio signals must be combined with carrier, can make the voice sig
9、nal to the distance. People listen to radio station radio program, is to receive the signal with low frequency electromagnetic waves The sending system and the receiving system two parts of Radio system mainly b. Radio is the basic process of signal transmission, the transmission, receiving process.
10、 After the sender, will need to spread information, such as voice, text, images, and low frequency signal, into electrical signal, through the modulator modulation in the high frequency carrier, and then by the transmitter through the antenna radiation to the air to, and with radio in the form of el
11、ectromagnetic wave propagation distance. In the receiver, These already modulation of high frequency radio receiver is the antenna down, after a series of treatment and demodulation, back into the original signals. Receiver is a kind of from the antenna and radio signal demodulation of the electroni
12、c equipment, mainly for the sound, image positioning information, etc. The radio of and radio receiver general special refers to receive only and the play of receivers, although other like TV technology is also radio receiving equipment. At present, the ground of radio and television points do VHF (
13、less or says m wave) and UHF (especially high frequency or say Fen Mi Bo) two frequency band. In our country, the frequency of use TV VHF frequency range is 48.5 MHz 300 MHz, divided into 1 12 channels, UHF band use frequency range is 470 MHz to 956 MHz, divided into: 3 68 channels. They basically a
14、re to rely on space wave propagation. The provisions of the international satellite radio and television have six frequency band, the main frequency band is 12KMHz, is also depend on space wave propagation. Receiver can receive the radio waves to the frequency range for receiver work frequency range
15、 or cover band. The working frequency of receiver and transmitter to the working frequency of corresponds, such as FM radio frequency range for the radio (88 108) MHZ, because of the transmitter FM radio frequency range for work also (88 108) MHZ 现代民用及军用设施使用电子设备繁多，电磁环境复杂，相互干扰严重。一般地，车、船和飞机上的通信设备收发机都集
16、成在一起。以短波通信设备为例，发射机的残余信号在接收机输入端产生的电平达 120dBV（即 13dBm）或更高。而接收机所需接收的微弱信号电平可能仅 -6 0dBV（即 -117 -113dBm）。因此，要求接收机处理的信号动态范围高达 120126dB。另外，高电平干扰信号与所接收信号频率仅相距数十千赫，所以，高电平干扰信号和它们在接收机中产生的互调产物会严重影响接收机的输出信噪比。为了降低这种影响，就要求接收机具有以下性质：高选择性，接收机的动态范围尽可能要大；高线性，在信道滤波之前，降低带外高电平干扰信号在信道滤波器通带内产生的互调产物；极低的本振相位噪声，以免邻近的干扰信号将本振噪声转
17、换到接收机信道带宽内。作为接收机重要组成部分的接收机 射频前端是接收机动态性能的关键部件，它工作于中频放大器之前。诸如动态范围、互调失真、 -1dB 压缩点和三阶互调截获点等，都与接收机前端的性能有直接关系。 无线电广播是利用无线电波向广大接收者播送声音节目的通信过程，属于无线电通信范畴。广播电台为了把声音信号传递出去，发射的电磁波必须带有音频信号。音频信号是通过一个调制器把各种声音信号加以处理而来的。它的频率很低，如人声的频率大约在 300Hz3000HZ,音乐频率大体在 50Hz 15000HZ，这样的频率是传送不出去的，必须再把低频信号加在高频电磁波里，这样的 过程叫做调制，未调制的高频
18、电磁波叫载波。音频信号必须与载波结合起来，才能把声音信号传送到远方。人们收听广播电台的广播节目时，就是接收到载有低频信号的电磁波 无线电广播系统主要由发送系统和接收系统两部分组成。无线电广播的基本过程是信号的发送、 传输 、接收 的 过程。在发送端，将需要传播的信息，如声音、文字，图像等低频信号，转换成电信号后 ,经调制器 “调制 ”在高频载波上，然后由发射机通过发射天线辐射到空中去，并以无线电电磁波的形式进行远距离传播。在接收端，这些已调制的高频无线电波被接收机天线接收下来，经过解调和一系列处 理后，回复成原来的低频信息。接收机是一种从天线接收并解调无线电信号的电子设备，主要用于声音，图像定
19、位信息等。 “收音机 和 “无线电接收机 ”一般特别指只接收和播放声音的接收机，尽管其他的象电视机技术也是无线电接收设备。 目前，地面的广播电视分做 VHF(甚高频或称米波 )和 UHF(特高频或称分米波 )两个频段。在我国， VHF 频段电视使用的频率范围是 48.5MHz 300MHz，划分成 1 12 频道，UHF 频段使用的频率范围是 470MHz 956MHz，划分成： 3 68 频道。它们基本上都是靠空间波传播的。国际上规定的卫 星广播电视有 6 个频段，主要频段是 12kMHz，也是靠空间波传播。接收机可以接收到的无线电波的频率范围为接收机的工作频率范围或波段覆盖。接收机的工作频率必须与发射机的工作频率相对应，如调频广播收音机的频率范围为（ 88 108）MHZ，是因为调频广播发射机的工作频率范围也为（ 88 108） MHZ
