User`s guide

224 Agilent E5505A User’s Guide
7 Residual Measurement Fundamentals
4
Measure the carrier-to-sideband ratio of the non-modulated side of the
phase detector. It must be at least 20 dB less than the modulation level 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 modulation level is set by the port-to-port isolation
of the power splitter and the isolation of the phase modulator. This
isolation can be improved at the expense of signal level by adding an
attenuator between the phase modulator and the power splitter.
5 Connect the phase detector.
6 Adjust the phase difference at the phase detector to 90 degrees
(quadrature) either by adjusting the test frequency or by adjusting an
optional variable phase shifter or line stretcher. Quadrature is achieved
when the meter in the phase noise software is set to center scale
(±2 mV).
7 Set the Type of Measurement to Phase Noise Without Using a PLL.
8 Set the Calibration Technique to Derive From Double-sided Spur and enter
the sideband amplitude and offset frequency.
9 Select New Measurement.
10 Check quadrature and measure the phase detector constant by pressing Y
to proceed.
11 Remove audio source.
12 Reset quadrature and measure phase noise data.
Single-Sided spur
This calibration option has the following requirements:
• A third source to generate a single sided spur
• An external power combiner (or directional coupler) to add the calibration
spur to the frequency carrier under test. The calibration spur must have an
amplitude –100 dB and –20 dB relative to the carrier amplitude. The offset
frequency of the spur must be 20 Hz and 20 MHz.
• A spectrum analyzer or other means to measure the single sided spur
relative to the carrier signal
You will find that the equipment setup for this calibration option is similar to
the others except that an additional source and a power splitter have been
added so that the spur can be summed with the input carrier frequency.
NOTE
For the system to accept the adjustment to quadrature, the meter must be within ±2 mV to
±4 mV.