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频域稳定度通常是通过谱密度来说明的。谱密度概念是简单而非常有用的,但在应用中必须小心。有若干不同但关系密切的谱密度,它们切合于信号的频率、相位、周期、振幅以及功率等的稳定度的规范和测量。本评述中将对一些有用的谱密度作扼要的指导性的叙述。叙述中包括(a)相位、(b)频率、(c)相对频率,(d)振幅,(e)时间间隔,(f)角频率以及(g)电压等的起伏的谱密度。还包括了射频功率的谱密度及其两个归一化成份,即草写的(f)和草写的 m(f),分别为相位调制和振幅调制部分。列出了这些不同谱密度中某些简单而常用的关系式。建议采用单边谱密度。阐述了与双边谱密度的关系式。讨论了这相关谱密度、与时间有关的谱密度的谱密度,以及平滑谱密度的概念。
Frequency domain stability is usually described by spectral density. The concept of spectral density is simple and very useful, but care must be taken in applications. There are a number of different but closely related spectral densities that are consistent with the specification and measurement of the stability of the signal’s frequency, phase, period, amplitude, and power. Some useful spectral densities will be briefly described in this commentary. The description includes (a) the phase, (b) the frequency, (c) the relative frequency, (d) the amplitude, (e) the time interval, (f) the angular frequency, and (g) the fluctuating spectral density of the voltage. Also includes the spectral density of radio frequency power and its two normalized components, namely, the sketch of (f) and the sketch of m (f), respectively, phase modulation and amplitude modulation part. Some simple and commonly used relationships among these different spectral densities are listed. It is recommended to use unilateral spectral density. The relationship between spectral density and bilateral is expounded. The related spectral density, the spectral density of time-dependent spectral density, and the concept of smooth spectral density are discussed.