HP 3048A Operating Manual page 200

1. Connect the hardware as shown for your
measurement. The beatnote signal should appear on
the HP 3561A (or on the RF spectrum analyzer if one is
connected to the system).
2. Note the frequency of the beatnote signal. If the
beatnote frequency is too low to resolve, decrease
the span setting on the HP 3561A by pressing the
3561A Span key on the HP 3048A or the Define Span
softkey on the HP 3561A. Continue decreasing the span
setting until the beatnote frequency can be easily read.
Notice the Center Volt.: label shown in the top right
corner of the HP 3048A display. The value displayed is
the Center Voltage of the VCO Tuning Curve specified
in the Instr. Params menu. This is the voltage level that
the HP 11848A TUNE VOLTAGE OUTPUT is currently
set to.
4. Press the |Center Voltage| softkey on the HP 3048A.
Notice that the center voltage value is incremented by
2% of the entered Voltage Tuning Range (shown in top
right corner) each time this key is pressed. (The value
can also be decremented by pressing the Shift key on
the keyboard and the | Center Voltage key at the same
time.) The voltage level at the TUNE VOLTAGE
OUTPUT is also incremented each time this key is
pressed.
Continue to increment the center voltage value until
you have increased it by 10% (five steps).
Observe the beatnote frequency change on the
HP 3561A resulting from the change in tune voltage.
The frequency change divided by the total voltage
change is the Tuning Constant in Hz/V of the VCO
source being tuned.
3-148 Signal Source Applications