Keysight Technologies N5511A, User Manual

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94 N5511A Phase Noise Test System User’s Guide
Absolute Measurement Fundamentals
Calibration
The model of a single sided spur is a narrow-band PM signal summed with an
amplitude modulated signal of the same depth. The summation constructively
adds in voltage to the upper sideband in this case and destructively adds to
the lower sideband. This has the effect of increasing the upper sideband by
6 dB and eliminating the lower sideband.
Figure 5-29 Single Sided Spur
When the phase modulation is detected in the phase detector, the AM
component is rejected. This detection process reveals the lower sideband but
reduces the upper sideband by 6 dB. The software takes this into account
during the calibration process.
Figure 5-30 AM and Carrier Removal
As a result, the measured cal tone by the system will be 6 dB lower compared
to the measured amplitude by the analyzer when setting the SSB tone. Figure
5-31 shows an example of spur set to -40 dBc at a 10 kHz offset, showing how
the system will detect a -46 dBc spur.
Figure 5-31 Measured Cal Tone