David Lee
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Posts: 29
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Hi Kappy, Phase noise spectrum, L(fm), is the power spectral density of the noisy oscillator waveform, measured around the fundamental, divided by the power of the noiseless oscillator waveform, at the fundamental. Adding noise to an oscillator does little to change the total signal power. So the area under the first power spectral density is the same as the area under the second power density, i.e. power conserves. Therefore, the area under the phase noise curve is always one. For typical oscillators, phase noise is below 0 dBc/Hz around the fundamental and away from the fundamental. For ultra-low-noise oscillators, phase noise is above 0 dBc/Hz at offsets less than 1 Hz. Measured phase noise can never be above 0 dBc/Hz at offsets larger than 1 Hz. If this were the case, the area under phase noise curve would exceed one. Carefully note that measured phase noise at carrier frequency is rarely 0 dBc/Hz. David
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