English: The Power Spectral Density of an oscillator can be depicted in dBc/Hz (logaritmic scale) or in W/Hz (linear scale). The x-axis is linear and centered on the fundamental frequency.
When the noise associated with the fundamental oscillation is important, the logarithmic representation gives a better focus.
Modeling is useful and important.
Modeling does not reach to the fundamental frequency, but gets very close. It is defined as Single Sideband and a logaritmic x-axis is preferred when representing it.
The most popular model was proposed by Leeson (February 1966)
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