N5511A Phase Noise Test System User’s Guide 177Residual and Additive Noise Measurement FundamentalsCalibrating the MeasurementUser entry of phase detector constantThis calibration option requires that you know the phase detector constant forthe specific measurement to be made. The phase detector constant can beestimated from the source power levels (or a monitor oscilloscope) or it can bedetermined using one of the other calibration methods. Once determined, thephase detector constant can be entered directly into the system softwarewithout going through a calibration sequence. Remember, however, that thephase detector constant is unique to a particular set of sources, the RF levelinto the phase detector and the test configuration.Advantages— Easy method for calibrating the measurement system.— Requires little additional equipment: only an RF power meter to manuallymeasure the drive levels into the phase detector or monitor oscilloscope.— Fastest method of calibration. If the same power levels are always at thephase detector, (as in the case of leveled outputs), the phase detectorsensitivity will always be essentially the same (within a dB or two). If thisaccuracy is adequate, it is not necessary to recalibrate.— Only one RF source is required.— Very quick method of estimating the phase detector constant and noisefloor to verify other calibration methods and check available dynamic range.Disadvantages— The user entry of the phase detector constant is the least accurate of all thecalibration methods.— Does not take into account the amount of power at harmonics of the signal.
