HP 70427A User Manual page 108

Millimeter Phase Noise Measurement - User Control
Step 5 - Decide which instrument to tune
There are three choices for phase locking: by using either the DUT; the
reference source; or for frequencies
be turned.
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 the modulation to DC FM.
Refer to the HP 3048A manual for more information on tuning the
HP 8662A/3A.
Tuning the HP 70472A
If the DUT is a room-temperature oscillator, the downconverter's LO should
be tuned. The downconverter's tuning sensitivity can be selected so that its
tuning range will be greater than the expected drift of the DUT. The choices
are:
•
1.0 ppm / V (600 MHZ PLL bandwidth must be greater
than the HP 3048A PLL bandwidth)
•
20 ppm/V
Tuning the DUT
Refer to the Signal Source Applications chapter of the HP 3048A manual
for information on tuning the DUT.
Step 6 - Select the downconverter's tuning sensitivity
Do this only if the Downconverter is being tuned.
1. Press the softkey.
Ref Chain
2. Press the
Tune Sens
3. Press the or the
1.0 ppm/V
Step 7 - Change the 600 MHz PLL bandwidth if needed
The only reason to use anything other than the default bandwidth is if the
downconverter is being tuned using 1.0 ppm/V sensitivity and the
HP 3048A system PLL bandwidth is greater than 10 kHz. If the
downconverter is being tuned, the 600 MHz phase-lock-loop bandwidth
must be wider than the HP 3048A system bandwith. Otherwise, the system
software can't accurately compensate for loop suppression.
1. Press the softkey.
Ref Chain
2. Press the
600 MHz PLL BW
≥
1.5.GHz the downconverter's LO can
softkey.
softkey.
20 ppm/V
softkey.
HP 70427A/HP 70428A User's Guide 3-9
Downconverter Operation
-8
of the output