The question of the uncertainty of a phase noise measurement is a vexed question which is difficult to answer well. This is partly because the measurement depends on so many parameters and some of these change with every measurement. A consequence of this is that the uncertainty of the measurement depends to a great extent on the device being measured. The work reported here describes some investigations into the effect of variation of some of the parameters with the particular intention of investigating the uncertainty of noise measurements made close to the carrier. Throughout this paper the method of making the phase noise measurements discussed is the phase detector method using a phase locked loop. This means that measurements close to carrier are inside the phase locked loop and that it is necessary to correct the noise measurement for the effect of the phase locked loop. The uncertainty of performing this correction is the main uncertainty which is investigated here.
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