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毕业设计
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多功能电子医药盒设计,毕业设计
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毕业设计（论文）中期报告 学院 班级 学生 姓名 指导 教师 课题名称： 多功能电子医药盒 简述开题以来所做的具体工作、取得的进展及下一步主要工作： 在毕业设计的最初阶段 , 认真阅读资料，了解蚕种新型消防车的基本原理及应用前景、其工作原理以及控制方法。并进行了以下几步工作： （ 1）、查找整理资料，学习相关知识。 （ 2）、经过查阅相关资料，选择比较可取的电路 ,对所设计的电路进行分析论证。 （ 3）、画出系统的流程，画出硬件设计图。 之后 ,分析各部分模块电路的具体作用，分析工作原理。查找元器件的主要功能特性、内部结构及各引脚的作用，尽量选择最适合的元器件，列元件清单，购买器件。根据之前整理的资料进行电路焊接。分模块的对电路进行调试，成功的调试完一些基本的单元电路，总结调试经验。 下一步的主要任务 : （ 1）、对未完成的电路继续制作。 （ 2）、对单片机软件进行初始的编程。 （ 3）、软件的后期调试及硬件电路的故障排除。 （ 4）、对整个电路进行系统调试，达到稳定，最后实现本课题所要实现的目标。 一周的时间进行毕业论文的准备 ,最后准备毕业答辩。 学生签字： 年 月 日 指导教师的建议与要求： 指导教师签字： 年 月 日 注：本表格同毕业设计（论文）一同装 订成册，由所在单位归档保存。 nts毕业设计（论文）任务书 题 目 (包括副标题 ) 多功能电子医药盒 教师姓名 职 称 系 别 学生姓名 学 号 班 级 成果形式 A 论文 B 设计说明书 C 实物 D 软件 E 作品 任务下达时间 2009 年 12 月 8 日 1毕业设计（论文）课题任务的内容和要求： 采用凌阳单片机的语音技术，传动技术，时间的记忆与存储技术。 主要技术要求：语音命令的正确识别。解读语音命令的发射。语音命令的接收。接收指令的执行。若这四个 技术指标都能完成，设计任务便基本完成。 。 语音辨识原理简图如下： 2毕业设计（论文）工作进度计划： 周 次 工作内容 早进入阶段 第 1-2 周 第 3-4 周 第 5-6 周 第 7-8 周 第 9-10 周 查找相关资料，完成开题，了解毕业设计涉及的问题。 收集资料，进行整理，学习单片机的相关知识，完成初步设计。 进行方案论证，结合设计任务的具体要求，正式确定设计方案。 购买元器件、准备必要的设备 ,焊接电路、调试。 调试硬件、软件测试毕业设计作品。 完成毕业论文 ,准备答辩。 教研室（学科组）主任签字： 声学模式训练 语音模型 复杂声学语音条件下的语音 输入 语音匹配 语音模式训练 语音处理 语言模型 识别结果理解结束 nts 多功能电子医药盒 Multi-function electronic medical box 摘 要 20 世纪中后叶，随着大规模晶体管集成电路制造工艺的飞速发展，使计算机渗透进城市的血液，成为人类社会生活中密不可分的一部分。越来越多种类的计算机投入社会生产，如果在人们的社会生活中所接触到的计算机均使用不同的、自身特有的人机接口，就要求计算机使用者掌握多种计算机操作语言，这无疑成为人们使用计算机的一大障碍。因此人与计算机的沟通成为了摆在人类面前崭新的课题。在音频压缩处理技术以及无线远程控 制技术高速发展的局面下，人们开始考虑使用人类语言作为新的方式和计算机进行无线远程对话。优化人机接口，使计算机智能化，并且能听懂远处传来的人类语言，以人类的方式思考，彻底摆脱复杂的计算机语言和繁琐的输入方式是今后发展的一大方向。台湾凌阳科技推出的 16 位 MCU-DSP 混合处理器 SPCE061A 可以实现上述的语音识别、数据编码等功能。因此 一款全新设计的人性化智能电子药盒，会说话，能 定时，更简单。 本次 设计为更多人带来了便利，尤其是对于众多不习惯于传统复杂定时系统的人们 使用多功能电子医药盒提高了人们的生活效率：针对 年轻人，可以在忙碌的工作时提醒吃药的时间；针对老年人，可以提醒按时吃药、安全吃药。 今后，根据智能电子医药盒的设计理念，可将其移植到其他小家电等具有实际意义的产品中去。在人类与计算机的关系日益密切的今天，更为便捷、更为人性化、更为智能化的人机对话方式无疑是今后科技发展的新趋势。 关键词 ： 人性化；语音辨识；定时自动开启药箱 ； SPCE061A nts ABSTRACT In the 20th century, with the large after IC manufacturing process of the transistor, the rapid development of computer penetrate into the blood and become human cities in social life is part of it. More and more kinds of computer into social production, if the peoples social life in contact with the computer use different, own human-machine interface, computer user requirements of computer language, mastering this undoubtedly become an obstacle of people use computers. So people and computer communication has become set before the human beings. In audio compression processing technology and wireless remote control technology rapid development situation, people began to consider using human language as a new way for wireless remote dialogue with the computer. Optimize human-machine interface, computer intelligence, and understand the distant human language in humans thinking mode, and get rid thoroughly sophisticated computer language and trival input method is one of the future development direction. Taiwan sunplus technology of 16 MCU SPCE061A microprocessor - DSP mix can be realized the speech recognition, data coding etc. Function. Therefore, a new design of human intelligence, ntscan speak, labels&tags electronic timing, can simpler. This design is more convenience, especially for many not accustomed to traditional complex timing system of people use muti _ function electronic medicine boxes to improve peoples lives for young people, efficiency: in the busy work can remind the medicine time, For the elderly, can remind medicine on time, the medicine safety. In the future, according to the intelligent electronic medicine box design concept, can be transplanted into other household appliances with practical significance to the product. The relationship between human and computer in todays increasingly close, more convenient and more intelligent, humanized is undoubtedly the man-machine dialogue mode in the new trend of development of science and technology. Key Words ： humanity;speech recognition;time automatically open medicine cabinet;SPCE061A nts 毕 业 论 文 开 题 报 告 多功能电子医药盒 系 别： 班 级： 学生姓名： 指导教师： 2009 年 12 月 8 日 nts 毕业论文开题报告 课题题目 多功能电子医药盒 课题性质 A B C D E 课题来源 A B C D 成果形式 A B C D E 同组同学 无 开题报告内容（见附页） 指导教师意见（课题难度是否适中、工作量是否饱满、进度安排是否合理、工作条件是否具备等） 指导教师签名： 月 日 专家组及系里意见（选题是否适宜、各项内容是否达到毕业设计（论文）大纲要求、整改意见等） 专家组成员签字： 教学主任（签章）： 月 日 nts附页： 开题报告 一、设计的目的与意义 随着我国 国民经济的发展，针对生活节奏的加快和 社会老龄化的趋势，结合产业发展需要，设计出了多功能电子医药盒。 我国现有的电子医药盒 从最简单的药瓶方式，到非常复杂的多层药箱 都有，在时间设定和语音的功能上，各式各样。但是现在还没有将时间设定、语音播放以及时 间的记忆集中在一起的电子医药盒。 国外的一些发达国家对用药的认知水平较高，在电子医药盒的研究和开发方面相对较好。虽然已经开发出体积很小的智能医药盒，同样，在功能上还没有将 时间设定、语音播放以及时间的记忆集中在一起的电子医药盒。 使用多功能电子医药盒提高了人们的生活效率：针对年轻人，可以在忙碌的工作时提醒吃药的时间；针对老年人，可以提醒按时吃药、安全吃药 二 、 工作原理 1. 设计思路 本项目设计三仓与多仓的电子药盒，支持设定每种药物的服用时间，自动提醒和控制仓盖开启，提示出药数量。同时，具有时间的记忆功 能。采用凌阳单片机的语音技术，传动技术，时间的记忆与存储技术。 2. 实现功能 采用凌阳单片机的语音技术，传动技术，记忆与存储技术最终实现： 1) 语音提示后， 仓盖开启和闭合的时间： 1 2s； 2) 药仓数量： 4 仓设计 ； 3) 能根据人的提示进行药物的选择； 4) 人性化设计与友好的人机界面； 5) 24 小时内任意设定 药物服用 提醒 ； 6) 语音互动，可以实现人机对话，具有小型机器人的识别能力； 7) 四仓设计，分为底仓、固定仓与常动仓，介绍如下： 底仓：为药物备用仓； 固定仓：针对家庭中常常需要服用药物的人所设计，服药时间、数量等可进行自行设定。 常动仓（分两层）：针对生活中的易发性疾病所设计，服药时间、数量等nts 可进行自行设定，具备语音识别功能，可根据语音提示，自动进行药物的选择。 8）具有时间的记忆功能； 3. 硬件结构 该系统可以被分为三个部分： 1）按键功能描述 时间调整键：可对现在时间及设定时间进行调整，可实现 5 路定时提醒：对于时间调整，可进行年月日小时分的设定 设定药物键：通过此键可进行服药位置、时间及数量（最大为 4）的设定，对于服药位置，可进行层数（最大为 3）与格数（最大为 6）的设定 采用默认键：通过此键无需设定，即可享用标准方案：位置：一层 2 格；时间：早上 8 时，数粒： 2 粒 紧急救护键：按下此键，可以拨打紧急电话，及时将情况通知给用户的子女，使老人尽快得到帮助。 2）定时的开启 当时钟计时达到预定时间，液晶自动显示药品位置、种类及服用量，语音播报液晶屏上显示的信息。同时，单片机控制步进电机迅速转动，自动开启药盒。一段时间后，进入休眠模式，同时，单片机控制步进电机迅速转动，自动关闭药盒。（药盒支持手动开启和定时自动开启两种方式） 产品功能图（如图） nts 三、课题的准备情况及进度计划 序号 毕业设计阶段性工作及成果 时间安排 1 收集资料确定设计方案 1 3 周 2 机械部分的设计与制作 4 6 周 3 电子控制电路系统设计 7 9 周 4 设计说明书、使用说明书编写 10 周 5 总体校核完成毕业设计 11 13 周 四、参考文献 1 刘海承等 . MCU-DSP 型单片机原理与应用 北京：北京航空航天大学出版社，2003:45 46. 2 罗亚非凌阳 16 位单片机应用基础北京：北京航空航天大学出版社， 2003: 4956. 3 郑学坚，周斌微型计算机原理及应用 第三版北京：清华大学出版社， 2001: 101104. 4 欧阳斌林，等单片机原理与应用中国水利水电出版社， 2001: 225 233. 5 李晶皎嵌人式语音技术及凌阳 16 位单片机应用北京：北京航空航天大学出版nts 社， 2003: 97 102. 6 潘松，黄继业 EDA 技术实用教程第二版北京：科学出版社， 2005: 234 237. 7 凌阳科技大学计划 .凌阳单片机在大学生电子竞赛中的应用，第一版，北京航空航天大学出版社， 2005: 175 179. 8 刘海成，秦进平 .MCU-DSP型单片机原理与应用基于凌阳 16位单片机，第一版，北京航空航天大学出版社， 2006: 215 216. 9 张齐，杜群贵 .单片机应用系统设计技术 基于 C语言编程，第二版，电子工业出版社， 2004 :191 193. 10 侯媛彬 .凌阳单片机原理及其毕业设计精选 ，第一版， 科学出版社 ， 2006:33 41. 11 吴双力，崔剑，王伯岭 .AVR-GCC与 AVR单片机 C语言开发，第一版，北京航空航天大学出版社， 2004:163 169. 12 徐煜明，韩雁 .单片机原理及接口技术，第一版，电 子工业出版社， 2005:57 58. 13 杨西明，朱骐 .单片机编程与应用入门，第一版，机械工业出版社， 2004:341 344. 14 严天峰 .单片机应用系统设计与仿真调试，第一版，北京航空航天大学出版社，2005:215 223. 15 Michael A. Miller.Data and Network Communications，第一版，科学出版社，2002:145 148. nts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. Fig.1 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 ntsselectivity 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 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 (), their frequency() and wavelength() being related , as for any wave motion, by the equation =* where =c=3.0*108 m/s in a vacuum (or air). If =300m, then =/=3.0*108 /(3.0*10 2)=106Hz=1MHz. The smaller is, the larger . nts Radio Waves can be described either by their frequency or their wavelength. But the former is more fundamental since, unlike (and ), 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 earths 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 frequency the greater the absorption. The range may be about 1500km at low frequencies (long wave, but much less for v. h. f.). Sky wave. This travels skywards and, if it is below a certain critical frequency (typically 30MHz), is returned to earth by the ionosphere. This consists of layers of air molecules (the D,E and F layer), stretching form about 80km above the earth to 50km, which have become positively charged through the removal of electrons by the suns ultraviolet radiation. On striking the earth the sky wave bounces back to the ionosphere where it is again gradually refracted and returned earthwards as if by reflection . This continues until it is completely attenuated. Space wave. For v. h . f., u. h. f. and microwave signals, only the space wave, giving line-of sight transmission, is effective. A range of up to 150km is possible on earth if the transmitting aerial is on high ground and there are no intervening obstacles such as hills, buildings or trees. Oscillators Electrical oscillators are widely used in radio and television transmitters and receivers, in signal generators, oscilloscopes and computers, to produce A.C. with waveforms which may be sinusoidal, square, sawtooth etc. and with frequencies from a few hertz up to millions of hertz. Oscillatory circuit When a capacitor discharges through an inductor in a circuit of low resistance, an A.C. flows. The circuit is said to oscillate at its natural frequency which, as we will show shortly, equals LC21 , i.e. its resonant frequency f0. Electrical resonance thus occurs when the applied frequency equals the natural frequency as it does in a mechanical system. In Fig,2(a) , a charged capacitor C is shown connected across a coil L.C immediately starts to discharge, current flows and a magnetic field is created which ntsinduces an e. m. f. in L. This e. m. f. opposes the current . When C is completely discharged the electrical energy originally stored in the electric field between its plates has been transferred to the magnetic field around L. Fig.2(b) oscillator Fig.2(a) The LC circuit By the time the magnetic field has collapsed, the energy is again stored in C. Once more C starts to discharge but current now flows in the opposite direction, creating a magnetic field of opposite polarity. When this field has decayed, C is again charged with its upper plate positive and the same cycle is repeated. In the absence of resistance in any part of the circuit , an undamped sinusoidal A.C. would be obtained. In practice , energy is gradually dissipated by resistance as heat and a damped oscillation is produced. Oscillator As the resistance of an LC circuit increases, the oscillation decay more quickly. To obtain undamped oscillations, energy has to be fed into the LC circuit in phase with its natural oscillations to compensate for the energy dissipated in the resistance of the circuit. This can be done with the help of a transistor in actual oscillators. A simple tuned oscillator is shown in Fig.2(b). The LC circuit is connected in the collector circuit (as the load) and oscillations start in it when the supply is switched on . The frequency of the oscillations is given by, i.e. then natural frequency of the LC circuit. The transistor merely ensures that energy is fed back at the correct instant from the battery. The current bias for the base of the transistor is obtained through R . AMPLIFIER Introduction The term amplifier is very generic. In general, the purpose of an amplifier is to take an input signal and make it stronger (or in more technically correct terms, ntsincrease its amplitude). Amplifiers find application in all kinds of electronic devices designed to perform any number of functions. There are many different types of amplifiers, each with a specific purpose in mind. For example, a radio transmitter uses an RF Amplifier (RF stands for Radio Frequency); such an amplifier is designed to amplify a signal so that it may drive an antenna. This article will focus on audio power amplifiers. Audio power amplifiers are those amplifiers which are designed to drive loudspeakers. Specifically, this discussion will focus on audio power amplifiers intended for DJ and sound reinforcement use. Much of the material presented also applies to amplifiers intended for home stereo system use. The purpose of a power amplifier, in very simple terms, is to take a signal from a source device (in a DJ system the signal typically comes from a preamplifier or signal processor) and make it suitable for driving a loudspeaker. Ideally, the ONLY thing different between the input signal and the output signal is the strength of the signal. In mathematical terms, if the input signal is denoted as S, the output of a perfect amplifier is X*S, where X is a constant (a fixed number). The * symbol means? Multiplied by. This being the real world, no amplifier does exactly the ideal, but many do a very good job if they are operated within their advertised power ratings. The output of all amplifiers contain additional signal components that are not present in the input signal; these additional (and unwanted)characteristics may be lumped together and are generally known as distortion. There are many types of distortion; however the two most common types are known as harmonic distortion and inter modulation distortion. In addition to the garbage traditionally known as distortion, all amplifiers generate a certain amount of noise (this can be heard as a background hiss when no music is playing). More on these later. All power amplifiers have a power rating, the units of power are called watts. The power rating of an amplifier may be stated for various load impedances; the units for load impedance are ohms. The most common load impedances are 8 ohms, 4 ohms, and 2 ohms (if you have an old vacuum tube amplifier the load impedances are more likely to be32 ohms, 16 ohms, 8 ohms, and maybe 4 ohms). The power output of a modern amplifier is usually higher when lower impedance loads (speakers) are used (but as we shall see later this is not necessarily better). In the early days, power amplifiers used devices called vacuum tubes (referred to simply as tubes from here on). Tubes are seldom used in amplifiers intended for DJ ntsuse (however tube amplifiers have a loyal following with musicians and hi-fi enthusiasts). Modern amplifiers almost always use transistors (instead of tubes); in the late 60s and early 70s, the term solid state was used (and often engraved on the front panel as a buzz word). The signal path in a tube amplifier undergoes similar processing as the signal in a transistor amp, however the devices and voltages are quite different. Tubes are generally high voltage low current devices, where transistors are the opposite (low voltage high current). Tube amplifiers are generally not very efficient and tend to generate a lot of heat. One of the biggest differences between a tube amplifier and a transistor amplifier is that an audio output transformer is almost always required in a tube amplifier (this is because the output impedance of a tube circuit is far too high to properly interface directly to a loudspeaker). High quality audio output transformers are difficult to design, and tend to be large, heavy, and expensive. Transistor amplifiers have numerous practical advantages as compared with tube amplifiers: they tend to be more efficient, smaller, more rugged (physically), no audio output transformer is required, and transistors do not require periodic replacement (unless you continually abuse them). Contrary to what many people believe, a well designed tube amplifier can have excellent sound (many high end hi-fi enthusiasts swear by them). Some people claim that tube amplifiers have their own particular sound. This sound is a result of the way tubes behave when approaching their output limits (clipping). A few big advantages that tube amplifiers have were necessarily given up when amplifiers went to transistors. What are Amplifier Classes? The Class of an amplifier refers to the design of the circuitry within the amp. There are many classes used for audio amps. The following is brief description of some of the more common amplifier classes you may have heard of. Class A: Class A amplifiers have very low distortion (lowest distortion occurs when the volume is low) however they are very inefficient and are rarely used for high power designs. The distortion is low because the transistors in the amp are biased such that they are half on when the amp is idling. As a result, a lot of power is dissipated even when the amp has no music playing! Class A amps are often used for signal level circuits (where power is small) because they maintain low distortion. Distortion for class A amps increases as the signal approaches clipping, as the signal is reaching the limits of voltage swing for the circuit. Also, some class A amps have speakers connected via capacitive coupling. ntsClass B: Class B amplifiers are used in low cost, low quality designs. Class B amplifiers are a lot more efficient than class A amps, however they suffer from bad distortion when the signal level is low (the distortion is called crossover distortion). Class B is used most often where economy of design is needed. Before the advent of IC amplifiers, class B amplifiers were common in clock radio circuits, pocket transistor radios, or other applications where quality of sound is not that critical. Class AB: Class AB is probably the most common amplifier class for home stereo and similar amplifiers. Class AB amps combine the good points of class A and B amps. They have the good efficiency of class B amps and distortion that is a lot closer to a class A amp. With such amplifiers, distortion is worst when the signal is low, and lowest when the signal is just reaching the point of clipping. Class AB amps (like class B) use pairs of transistors, both of them being biased slightly ON so that the crossover distortion (associated with Class B amps) is largely eliminated. Class C: Class C amps are never used for audio circuits. They are commonly used in RF circuits. Class C amplifiers operate the output transistor in a state that results in tremendous distortion (it would be totally unsuitable for audio reproduction). However, the RF circuits where Class C amps are used employ filtering so that the final signal is completely acceptable. Class C amps are quite efficient. Class D: The concept of a Class D amp has been around for a long time, however only fairly recently have they become commonly used. Due to improvements in the speed, power capacity and efficiency of modern semiconductor devices, applications using Class D amps have become affordable for the common person. Class D amplifiers use a very high frequency signal to modulate the incoming audio signal. Such amps are commonly used in car audio subwoofer amplifiers. Class D amplifiers have very good efficiency. Due to the high frequencies that are present in the audio signal, Class D amps used for car stereo applications are often limited to subwoofer frequencies, however designs are improving all the time. It will not be too long before a full band class D amp becomes commonplace. Other classes: There are many other classes of amplifiers, such as G, H, S, etc. Most of these are variations of the class AB design, however they result in higher efficiency for designs that require very high output levels (500W and up for example). At this time I will not go into the details of all of these other classes as I have not studied them all in detail. Suffice to be aware that they exist for now. nts中文译文 无线电接收机 图 1 为无线电接收机的方框图 ,输入信号为调幅无线电波。它的基本组成包括天线、调谐回路、混频器、本振电路、中放放大器、检波器、音频放大器、喇叭、电源等。 图 1 无线电接收机框图 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。 尽管接收的有用信号来自几千里以外，但如果经过放大，通过天线获得的信号还是具有令人满意的效果。放大过程可能应用在对检波前的射频电流，这种情况称为射频放大；也可应于检波后，这种情况称为音频放大。 放大器的应用使令人满意的接收成为可能，否则，有些太弱的信号不能获得好的收听效果。 从射频信号中重视被传输的原始信号的过程称为检波或解调。如果有用信号在发射时是通过改变信号的振幅（即调幅），则检波就是通过对射频电流进行整流完成的。整流电流随着原始调制信号而变化，从而冲县了原始的有用信号，这样，已调波被整流而产生的电流可以被看成随原始信号幅度变化的平均值电流。 接收机的电路由多级组成。每级由晶体管与提供工作电压、电流和信号电压、nts电流的元件相连构成，每级都有输入回路，它让信号进入；有输出回路，它让通常是放大后的信 号输出。当一级接一级时，第一级的输出回路将信号馈送给第二级，信号经过逐级放大，直到足以推动扬声器。 无线电波 无线电波是电磁波大家族中的一员，它们携带能量且以光速在空气中传播，它们的频率与波长相关，即任何电磁波传播时，有 =* 这里， =c=3.0*108 m/s （在空气中），如果 =300m, 则 =/=3.0*108 /(3.0*10 2)=106Hz.=1MHz。波长 越小，频率 越高。 无线电波既能用频率又能用波长来描述。但前者更常用，因 为频率不像速度，不会因传播媒介的改变而变化。 从天线电波辐射出去的无线电波通常以三种形式传播。 （ a）地表波或地波。这种波按地球表面的曲度，沿地表面传播。它的传播范
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