中英文翻译--校园自动锁相调频发射原理{修}

INTELL IGENT FREQUENCY MODULATI ON OF CAMPUS
BROADCASTING SYSTEM
FM radio is the way the FM audio signal transmission, the carrier wave frequency modulation with the audio signal changes center frequency in the carrier (not the center frequency modulation ago) on both sides of change, second change the offset frequency and audio signal the same modulation frequency, such as the frequency of audio signal 1KHz, the carrier frequency offset changes in the number of times per second 1K. The size of offset with the amplitude of audio signal size. FM transmitters in the domestic Specifications limit to allow the maximum frequency offset ±75KHz, the frequency response 80-10000Hz (±3dB), harmonic radiation-60dB (for a fundamental 0dB), the frequency stability of 1 ×10-6, letter noise ratio ≥ 50dB, total harmonic distortion ≤ 0.1%, transmitting frequency 87 - 108MHz, the general provisions of the school in the 70 - 87MHz between.
Intelligent broadcasting system on campus as an innovative and practical equipment of modern education, in line with the country's industry and the Ministry of Education's education-oriented information to and is widely considered an alternative school of traditional e-ring and ear-piercing loudspeakers broadcasting the green environment-friendly products. The system with the latest computer numerical control technology, high-fidelity audio technology, created the music (or music ring tones) instead of e-ring precedent. Broadcast system, which is indispensable for each school, one of the infrastructure, although in recent years video and network technology in the rapid development of the broadcasting system but still its practicality, economy, convenience was a variety of units, places of application . Existing types of schools in China are basically the public address system, it mainly used for various public occasions, such as all of public broadcasting, notification, broadcast a variety of literary and artistic programs, recognition of advanced school to convene the General Assembly, such as . With modern information technology, multi-media teaching in schools to keep Xinhuanet widely popular, the majority of primary and secondary schools to use voice broadcasting system of language teaching in the continuing increase in demand, the traditional school public address system for broadcasting a number of small-scale, such as: canteen meals put on music, at different levels on different classes of voice training in the morning and evening broadcasts of quarters have a choice of broadcasting difficult to achieve. Schools can
not meet the teaching voice, voice training needs. Smart campus FM radio system is based on the current school system functions on the campus radio growing demand to develop a set of interactive intelligent FM radio system, it has no wiring Pole, covering a wide range of unlimited expansion, installation and maintenance convenience, investment Province, a beautiful clear sound quality characteristics. The system is currently a set of more advanced intelligent broadcasting system.
Since the birth of radio technology, information transmission and information processing has always been its major task. To effectively launch a radio signal out, the size of the antenna and the signal wavelength must be the same order of magnitude. In order to effectively carry out transmission, must be to bring information to the dozens of low-frequency signal modulation MHz ~ more than a few hundred MHz high-frequency oscillation signal, and then sent by the antenna. In order to reduce the factors that caused instability in the system, and enhance the reliability of the system, the system must include automatic gain control, automatic frequency control and automatic phase control (PLL) circuit including the feedback control. The performance of phase-locked loop circuit in which it is particularly important The use of phase-locked loop FM programs directly, so that it not only has a very high frequency stability (about 10-6), also has a relatively high amount of the maximum offset. The overall integration of the FM transmitter control signals, used as the core of the BH1417 chip circuit design, chip crystal oscillator to provide benchmarks for the oscillation frequency signal source, the source oscillation frequency synthesizer using PLL mode. The use of FM modulation signal is added directly onto the realization of voltage-controlled oscillator. VCO varactor diodes and by the BJT oscillator composed of three-point capacitance. RF power amplifier using a high efficiency Class C amplifier.
BH1417-house consists of three basic components: phase detector (PD), loop filter (LPF) and voltage-controlled oscillator (VCO). Phase detector is a phase comparison device, the input signal Si (t) and voltage-controlled oscillator output signal So (t) to compare the phase, resulting in two signals corresponding to the error voltage phase Se (t). Loop filter is to filter out the error voltage Se (t) in the high frequency components and noise in order to ensure the performance of the requested loop to increase the stability of the system. VCO control voltage by Sd (t) the control, so that the frequency of VCO frequency to the input signal side, until the elimination of the lock frequency difference. Phase-locked loop phase error is a real control
system. By comparing the input signal and VCO phase difference between output signals, resulting in the error control voltage to adjust the VCO frequency, so as to achieve the same frequency with the input signal. Began its work in the loop, if the input signal frequency and voltage-controlled oscillator frequency is different from the two signals due to the inherent frequency between the poor, is bound to have been changes in phase difference, phase detector output voltage on the error within a certain range change. In this error voltage control, voltage-controlled oscillator frequency is changing. If the voltage-controlled oscillator to change the frequency of the input signal with frequency equal to the stability conditions are met in this frequency stabilized. Achieve stability, the input signal and VCO output signal frequency difference between the zero, a difference of no change over time, the error voltage to a fixed value into the loop on the "lock" state.
Loudspeakers broadcast the selected environment should in principle be selected as the specifications of different species such as the radio speakers, the ceiling in the ceiling of the room, to use the embedded, non-after speaker enclosures of smallpox. Simple structure of these speakers, but the prices are relatively cheap, and easy construction. The main drawback is that after the cover is not easily insects, rodents bite. The only framework in the ceiling without the ceiling of the interior surface (such as open-frame shopping malls) to use the lifting-style ball after the speaker or speaker enclosure ceiling. Due to a ceiling equivalent to the infinite baffle, so the conditions in the ceiling under the hood after the use of loudspeakers will not cause a short circuit. And there is no ceiling when the situation is very different, if still free of smallpox after speaker enclosures, the effect will be poor. In principle, should be used when hoisting speaker. However, too large investment and can also be used for smallpox after the speaker enclosures. After the speakers have rear hood cover smallpox is not only the role of the general mechanical protection, and to some extent play the role of anti-short-circuit.
校园自动锁相调频发射原理
调频广播是以调频方式进行音频信号传输的，调频波的载波随着音频调制信号的变化而在载波中心频率（未调制以前的中心频率）两边变化，每秒钟的频偏变化次数和音频信号的调制频率一致，如音频信号的频率为1KHz，则载波的频偏变化次数也为每秒1K次。

频偏的大小是随音频信号的振幅大小而定。

在国内调频发射机技术指标允许最大频偏限制在±75KHz，频率响应80-10000Hz（±3dB），谐波辐射强度-60dB（以基波为0dB），频率稳定度1×10-6，信噪比≥50dB，失真度≤0.1%，发射频率87--108MHz，学校一般规定在70--87MHz 之间。

校园智能广播系统作为一种新颖实用的现代教育设备，符合国家的产业导向和教育部的教育信息化要地，被广泛认为是替代学校传统电子铃声和刺耳高音喇叭广播的绿色环保型产品。

该系统凭借最新的计算机数字控制技术、高保真音响技术，开创了以音乐（或音乐铃声）代替电子铃声的先例。

广播系统是每个学校不可缺少的基础设施之一，尽管近几年来视频技术和网络技术在飞速的发展，但广播系统仍以它的实用性、经济性、便捷性被各种单位、场所应用。

我国现有的各类学校基本上都有公共广播系统，它主要用于各种公共场合，如进行全校的公共广播、通知、课间操、播送各种文艺节目、表扬先进、召开全校大会等。

随着现代信息技术的不断发展，多媒体教学在广大中小学校不断普及，广大中小学利用广播系统进行语音语言教学的需求在不断的增加，传统的公共广播系统对于学校一些小规模的广播，如：就餐时对食堂放音乐、不同年级不同班级上语音训练课、早晚对宿舍广播等有选择的广播难以实现。

也不能满足学校语音教学、语音训练的需求。

校园智能调频广播系统是根据当前学校对校园广播系统功能的要求不断增加，开发的一套交互式智能调频广播系统，它具有无需立杆架线，覆盖范围广，无限扩容，安装维护方便，投资省，音质优美清晰的特点。

该系统是目前国内较为先进的一套智能广播系统。

无线电技术诞生以来,信息传输和信息处理始终是其主要任务。

要将无线电信号有效地发射出去,天线的尺寸必须和电信号的波长为同一数量级。

为了有效地进行传输,必须将携带信息的低频电信号调制到几十MHz～几百MHz以上的高频振荡信号上,再经天线发送出去。

为减小各种因素引起的系统不稳定，增强系统的可靠性，系统必须包括自动增益控制、自动频率控制和自动相位控制(锁相环)在内的反馈控制电路。

其中锁相环电路的性能就显得尤其重要。

采用锁相环直接调频的方案，使其不仅具有很高的频率稳定度（约10-6），还具有比较高的最大频偏量。

整体集成化控制信号的调频发射，采用芯片BH1417为核心的电路设计，芯片内晶振为振荡源提供基准频率信号，振荡源采用PLL
频率合成方式。

调频利用调制信号直接加到压控振荡器上来实现的。

压控振荡器由变容二极管和晶体三极管组成电容三点式振荡器。

射频功率放大器采用效率比较高的丙类功放。

BH1417内部由三个基本的部件组成：鉴相器（PD）、环路滤波器（LPF）和压控振荡器（VCO）。

鉴相器是个相位比较装臵，把输入信号Si(t)和压控振荡器的输出信号So(t)的相位进行比较，产生对应于两个信号相位差的误差电压Se(t)。

环路滤波器的作用是滤除误差电压Se(t)中的高频成分和噪声，以保证环路所要求的性能，增加系统的稳定性。

压控振荡器受控制电压Sd(t)的控制，使压控振荡器的频率向输入信号的频率靠拢，直至消除频差而锁定。

锁相环实质是个相位误差控制系统。

通过比较输入信号和压控振荡器输出信号之间的相位差，从而产生误差控制电压来调整压控振荡器的频率，以达到与输入信号同频。

在环路开始工作时，如果输入信号频率与压控振荡器频率不同，则由于两信号之间存在固有的频率差，相位差势必一直在变化，鉴相器输出的误差电压就在一定范围内变化。

在这种误差电压的控制下，压控振荡器的频率也在变化。

若压控振荡器的频率能够变化到与输入信号频率相等，在满足稳定性条件下就在这个频率上稳定下来。

达到稳定后，输入信号和压控振荡器输出信号之间的频差为零，相差不再随时间变化，误差电压为一固定值，环路就进入“锁定”状态。

广播扬声器的选用原则上应视环境选用不同品种的规格的广播扬声器例如，在有天花板吊顶的室内，宜用嵌入式的，无后罩的天花扬声器。

这类扬声器结构简单，价钱相对便宜，又便于施工。

主要缺点是没有后罩，易被昆虫、鼠类啮咬。

在仅有框架吊顶面无天花板的室内（如开架式商场）宜用吊装式球型音箱或有后罩的天花扬声器。

由于天花板相当于一块无限大的障板，所以在有天花板的条件下使用无后罩的扬声器也不会引起短路。

而没有天花板时情况就大不相同，如果仍用无后罩的天花扬声器，效果会很差。

这时原则上应使用吊装音箱。

但若嫌投资大，也可用后罩的天花扬声器。

有后罩天花扬声器的后罩不仅有一般的机械防护作用，而且在一定程度上起到防上声短路的作用。