1.射频和无线通信系统介绍
概述
This tutorial is part of the National Instruments Measurement Fundamentals ries. Each tutorial in this ries teaches you a specific topic of common measurement applications by explaining the theory and giving practical examples. This tutorial covers an introduction to RF, wireless, and high-frequency signals and systems.
本教程是测量NI基础系列的一部分。本系列教程中的每一个指南结合理论解释和实际的例子教你常用的测量应用。本教程介绍介绍了射频，无线和高频信号与系统。
For the complete list of tutorials, return to the NI Measurement Fundamentals Main page, or for more RF tutorials, refer to the NI RF Fundamentals Main subpage.
对于教程的完整清单，请返回NI Measurement Fundamentals Main page,或更多的射频教程，请参阅NI RF Fundamentals Main subpage.
目录
1. Marconi and the First Wireless Transmissions 马可尼和第一次无线传输
2. What is RF? 射频是什么？
3. Why Operate at Higher Frequencies? 为什么工作在更高的频率？
4. Frequency Shifting through Frequency Mixing 通过混频移频
5. Looking for more RF Basics? 寻找更多的射频基础知识？
6. Relevant NI Products
7. Conclusions 结论
Marconi and the First Wireless Transmissions
Radio Frequency (RF) and wireless have been around for over a century with Alexander Popov and Sir Oliver Lodge laying the groundwork for Guglielmo Marconi’s wireless radio developments in the early 20th century. In December 1901, Marconi performed his most
prominent experiment, where he successfully transmitted Mor code from Cornwall, England, to St John’s, Canada.
在亚历山大波波夫爵士和奥利弗洛奇奠定了20世纪初马可尼无线电台的基础时，射频（RF）和无线已经出现了一个世纪。在1901年12月，马可尼进行他最杰出的实验，在那里他成功从英国康沃尔发送莫尔斯码到加拿大圣约翰。
What is RF? 什么是射频？
RF itlf has become synonymous with wireless and high-frequency signals, describing anything from AM radio between 535 kHz and 1605 kHz to computer local area networks (LANs) at 2.4 GHz. However, RF has traditionally defined frequencies from a few kHz to roughly 1 GHz. If one considers microwave frequencies as RF, this range extends to 300 GHz. The following two tables outline the various nomenclatures for the frequency bands. The third table outlines some of the applications at each of the various frequency bands.
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RF本身已成为无线和高频信号的代名词，它包括了535kHz~1605kHz的调幅无线电到2.4
GHz的计算机局域网（LAN）之间的任何频率。然而，传统定义的RF从几kHz的频率至大约读者卷首语1GHz。如果把微波频率考虑作为射频，这个范围扩展到300GHz。以下两个表概述了各频段的术语。第三表列出了在不同频段的一些应用。
Table 1: Frequency Band Designations
Table 1 shows a relationship between frequency (f) and wavelength (λ). A wave or sinusoid can be completely described by either its frequency or its wavelength. They are inverly proportional to each other and related to the speed of light through a particular medium. The relationship in a vacuum is shown in the following equation:
where c is the speed of light. As frequency increas, wavelength decreas. For reference, a 1 GHz wave has a wavelength of roughly 1 foot, and a 100 MHz wave has a wavelength of roughly 10 feet.
表1显示了频率（f）和波长（唐朝李牧λ）的关系。波或正弦波可以完全由其频率或波长描述。他们成反比关系，并与通过特定媒介的光速有关。在真空的关系如公式如下：。其中c是光速。随着频率的增加，波长减小。作为参考，1 GHz的波具有波长约为1英尺，100 MHz的波有大约10英尺的波长。
Table 2: Microwave Letter Band Designations
Table 3: Frequency Applications and Allocations in the U.S.
RF measurement methodology can generally be divided into three major categories: spectral analysis, vector analysis, and network analysis. Spectrum analyzers, which provide basic measurement capabilities, are the most popular type of RF instrument in many general-purpo applications. Specifically, using a spectrum analyzer you can view power-vs-frequency information, and can sometimes demodulate analog formats, such as amplitude modulation (AM), frequency modulation (FM), and pha modulation (PM).
Vector instruments include vector or real-time signal analyzers and generators. The instruments analyze and generate broadband waveforms, and capture time, frequency, pha, and power information from signals of interest. The instruments are much more powerful than spectrum analyzers and offer excellent modulation control and signal analysis.
Network analyzers, on the other hand, are typically ud for making S-parameter measurements and other characterization measurements on RF or high-frequency components. Network analyzers are instruments that correlate both the generation and analysis on multiple channels but at a much higher price than spectrum analyzers and vector signal generators/analyzers.
射频测量方法大致可以分为三大类：频谱分析，矢量分析和网络分析。频谱分析仪，它提供基本的测量功能，在许多通用应用中是最受欢迎的RF仪器类型。具体来说，使用频谱分析仪可以查看功率与频率的信息，有时可以解调模拟格式，如调幅（完美的近义词AM），调频（FM）和相位调制（PM）。褥疮用什么药膏最好
矢量仪器包括矢量或实时信号分析仪和发生器。这些仪器分析和产生宽带波形，并从感兴趣的信号捕获时间，频率，相位，功率信息。这些仪器比频谱分析仪功能强大，提供优良的调制控制和信号分析。
网络分析仪通常用于射频或高频元件的S -参数测量及其他特性的测量。网络分析仪通过多通道融合了信号产生和信号分析，但是它的价格比频谱分析仪和矢量信号发生器/分析仪要高。
优雅的句子Why Operate at Higher Frequencies?
为什么工作在更高的频率？
From Table 3 we notice that the frequency spectrum is quite fragmented and den. This encompass one of the reasons that we are constantly pushing applications into higher and higher frequencies. However, some of the other reasons accounting for this push into higher frequencies include efficiency in propagation, immunity to some forms of noi and impairments as well as the size of the antenna required. The antenna size is typically related to the wavelength of the signal and in practice is usually ¼乱投医 wavelength.
燕窝小孩能吃吗This leads to a very interesting question. Typically, data is structured and easily reprented at low frequencies; how can we reprent it or physically translate it to the higher RF frequencies? For example, the human audible range is from 20 Hz to 20 kHz. According to the Nyquist theorem, we can completely reprent the human audible range by sampling at 40 kHz or, more precily, at 44.1 kHz (this is where stereo audio is sampled). Cell phones, however, operate at around 850 MHz. How does this happen?
