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Residual Measurement Fundamentals
The Calibration Options
3. Measure the carrier-to-single-sided-spur ratio out of the coupler at the
phase detector's modulated port and the offset frequency with the RF
spectrum analyzer. The RF calibration source should be adjusted such
that the sidebands are between –30 and –60 dB below the carrier and the
frequency offset of the spur between 10 Hz and 50 MHz.
Figure 8-16
Carrier-to-spur Ratio of Modulated Signal
4. Measure the carrier-to-spur ratio of the non-modulated side of the phase
detector. It must be at least 20 dB less than the spur ratio of the
modulated port. This level is necessary to prevent cancellation of the
modulation in the phase detector. Cancellation would result in a smaller
phase detector constant, or a measured noise level that is worse than the
actual performance. The isolation level is set by the port-to-port
isolation of the power splitter and the isolation of the –20 dB coupler.
This isolation can be improved at the expense of signal level by adding
an attenuator between the coupler and the power splitter.
8-26 Agilent Technologies E5500 Phase Noise Measurement System
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