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Tunable Source Operation
Phase Noise Measurement With PLL
Tuning the HP 8662A/3A
If the DUT is referenced to an oven stabilized oscillator, the HP 8662A/3A
can be tuned. Connect the tune line to the EFC input. The limitation is that
the HP 8662A/3A's EFC can only track a drift of 10
frequency from the downconverter.
The HP 8662A/3A can also be tuned by setting modulation to DC FM, but
phase noise for offsets <10 kHz will be degraded. Refer to the HP 3048A
manual for more information on tuning the HP 8662A/3A.
If the HP 3662/3A is the VCO go to step 7 below.
Tuning the HP 70428A Option 002
The HP 70428A Option 002 has several tuning sensitivities. The choices are:
•
0.05 ppm/V: Use this sensitivity if the DUT is locked to a
crystal-controlled, temperature-stabilized reference.
•
1.0 ppm/V: Use this sensitivity if the DUT is referenced to
an ambient temperature crystal oscillator. (600 MHz PLL
bandwidth must be greater than HP 3048A PLL
bandwidth)
•
20 ppm/V: Use this sensitivity if the 1.0 ppm/V sensitivity
does not provide adequate drift tracking.
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.
Step 5 - Select HP 70428A Option 002 tuning sensitivity
Do this only if the HP 70428A Option 002 is being tuned.
First determine which sensitivity to use as described below:
The HP 70428A Option 002 tuning sensitivity must be selected so that its
tuning range will be greater than the expected drift to the DUT. The left
column of the following table shows the choices.
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 HP 70428A TUNE VOLTAGE OUTPUT
connector and the HP 70428A Option 002's VOLTAGE CONTROL input.
This forces the system to select a phase-lock-loop bandwidth that is much
less than 100 MHz PLL bandwidth of 126 Hz in the HP 70428A Option
002's reference chain.
5-4 HP 70427A/HP 70428A User's Guide
–8
of the output
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