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通信电子线路课程设计说明书
三极管混频器
系 、 部： 电气与信息工程系 学生姓名： 指导教师： 职称 讲师 专 业： 电子信息工程 班 级： 完成时间： 2010年12月20日
摘 要
混频器在通信工程和无线电技术中，应用非常广泛，在调制系统中，输入的基带信号都要经过频率的转换变成高频已调信号。在解调过程中，接收的已调高频信号也要经过频率的转换，变成对应的中频信号。特别是在超外差式接收机中，混频器应用较为广泛，如AM 广播接收机将已调幅信号535KHZ-一1605KHZ要变成为465KHZ中频信号，电视接收机将已调48．5M一870M 的图象信号要变成38MHZ的中频图象信号。移动通信中一次中频和二次中频等。在发射机中，为了提高发射频率的稳定度，采用多级式发射机。用一个频率较低石英晶体振荡器做为主振荡器，产生一个频率非常稳定的主振荡信号，然后经过频率的加、减、乘、除运算变换成射频，所以必须使用混频电路，又如电视差转机收发频道的转换，卫星通讯中上行、下行频率的变换等，都必须采用混频器。由此可见，混频电路是应用电子技术和无线电专业必须掌握的关键电路。
人们一直都在寻求快速远距离通信的手段。但是，直到十八世纪中叶才有了现代意义上的快速远距离通讯手段，这归功于无线电的发明。一个多世纪以来，通信的方式和内容不断更新发展，从最初的莫尔斯电码到现在的卫星通讯，现代通讯技术正成为人们日常生活中越来越重要的角色。作为无线传输体系中不可缺少的重要环节，混频技术，如晶体管混频，二极管混频以及场场效应管混频等，被广泛应用于各种通讯设备中， 实现信号频谱的搬移。
混频的用途是广泛的，它一般用在接收机的前端。除了在各类超外差接收机中应用外在频率合成器中为了产生各波道的载波振荡，也需要用混频器来进行频率变换及组合在多电路微波通信中，微波中继站的接收机把微波频率变换为中频，在中频上进行放大，取得足够的增益后，在利用混频器把次中频变换为微波频率，转发至下一站此外，在测量仪器中如外差频率计，微伏计等也都采用混频器。因此，做有关混频电路的课题设计很能检验对高频电子线路的掌握程度；通过混频器设计，可以巩固已学的高频理论知识。
此外为辅助电路，此次的课程设计还应用了LC谐振回路以及RC二阶有源滤波器，以实现对干扰信号的有效抑制。
关键词： 混频器；超外差接收机；有源滤波器
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ABSTRACT
The mixer in communication engineering and radio technology, are widely used in the modulation system, the input of baseband signal are through frequency conversion become already tuning frequency signal. In the process, receiving demodulation already tuning frequency signal also should pass frequency conversion, become the corresponding mid-frequency signal. Especially in specialized superheterodyne receivers of type, mixers are more widely application, such as kfi-am radio receiver will be already amplitude modulated signal 535KHZ - a 1605KHZ to become 465KHZ mid-frequency signal, for television receiver will have a 870M 4.85 M tone of image signal to become 38MHZ of intermediate frequency image signal.
people are always looking for fast way to communicate over distance, to transfer or to exchange information. Modern long distance communication technology was invented in mid of 18th century thanks to the invention of radio technology. Since then, this technology was well developed and many new methods came out. From Morse code to satellite, modern communication is playing more and more important role. As a key part of radio technology – mixing, e.g. transistor mixer, diode mixer and FET mixer, etc. are broadly used in different system，to shift frequency.
The figure hereafter illustrated the basic components of a communication There are kinds of communication technology; they are not going to be introduced here one by one. However most of the transmitters and receivers are made by RF system. The topic of this document is to design and simulate a key unit circuit of wireless communication system --- mixer.
Mixing technology is very useful; normally they are applied by the front end of receiver. They are used by superheterodyne receiver, frequency synthesizer, microwave repeater and instruments. Therefore, this kind of design practice can greatly help to understand RF knowledge well.
Furthermore, as auxiliary circuit, LC network and RC active filter are applied to this design, to effectively eliminate interference.
KEYWORDS
mixers；specialized superheterodyne receivers；sctive filter
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system.