We know that the spectrum is the most important resource for wireless communications. The spectrum is short for frequency spectral density and is the frequency distribution curve. The distribution curve is tested by the spectrum analyzer, which can not be seen by the naked eye. Complex oscillations are decomposed into harmonic oscillations of different amplitudes and different frequencies, and the patterns of the amplitude of these harmonic oscillations arranged in frequency are called spectra. The spectrum is widely used in acoustics, optics and radio technologies.There also are other Electronic Instruments.
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