HP 70427A User Manual page 145

Source Operation
Phase Noise Measurement With PLL
Noise performance depends on tuning sensitivity so it may be necessary to
trade off noise performance for tuning range. Refer to the specification table
in chapter 9 for noise performance for each tuning sensitivity.
When the 0.05 ppm/V tuning sensitivity is used, a 10 dB pad must be
inserted in the tune line between the HP 11848A's TUNE VOLTAGE
OUTPUT connector and the HP 70428A K01 Tune Voltage Supply. This
forces the system to select a phase lock loop bandwidth that is much less
than the 100 MHz PLL bandwidth of 126 Hz in the HP 70428A's reference
chain.
Table 4-1 Tuning Sensitivity
Source Tuning
Sensitivity
.05 ppm/V
1 ppm/V
20 ppm/V
The middle and right columns of the above table show how the frequency
accuracy and drift characteristics of the DUT determine which tuning
sensitivity to select. These two columns of the table are described below:
DUT Max Drift
This column shows how much the DUT frequency can drift and still be
tracked by the HP 70428A.
DUT Freq Accuracy
This column shows how close the DUT must be to the nominal frequency of
the HP 70428A in order to be sure that its frequency can be pulled to the
DUT frequency during a measurement. The accuracy value takes into
account the full tuning range of the HP 70428A plus its absolute accuracy.
Then, enter the tuning sensitivity as follows:
1. Press the
2. Press the
3. Press the
Step 5 - Change the source's PLL bandwidths if needed
The only reason to use anything other than the default bandwidths is if the
source is being tuned using the 0.05 ppm/V or 1.0 ppm/V tuning sensitivity
and the HP 3048A system PLL bandwidth is not much less than the
4-4 HP 70427A/HP 70428A User's Guide
DUT Max DUT Freq
Drift accuracy
–9
2×10
1 ppm 5 ppm
20 ppm 60 ppm
softkey.
Ref Chain
softkey.
Tune Sens
, , or
0.05 ppm/V 1.0 ppm/V
–7
2×10
softkey.
20 ppm/V