HP E4418A, Service Manual

Page: 66 / 108

Adjustments
Power Reference Oscillator Level Adjustment
3-8 HP EPM-441A/442A Service Guide
Equipment
Test power meter ................................... HP 432A
Thermistor Mount ................................ HP 478A Option H75
Digital Voltmeter (DVM)....................... HP 3456A
Procedure
Note
The procedure details the key presses required on the
HP EPM-441A. For the HP EPM-442A the equivalent key presses
should be performed on both channels.
1. Set up the DVM to measure resistance. Connect the DVM between
the V
RF
connector on the rear panel of the HP 432A and pin 1 on
the thermistor mount end of the sensor cable. Verify that no power
is applied to the HP 478A
2. Round off the DVM reading to two decimal places and record this
value as the internal bridge resistance (R) of the test power meter
(approximately 200
Ω
).
■
R (Internal Bridge Resistance)_______________
Ω
3. Connect the equipment as shown in Figure 3-3. The leads should
be isolated from ground. Ensure that the power reference
oscillator is off. Ensure that both the power meter under test and
the HP 432A have been powered on for at least 30 minutes before
proceeding to the next step.
4. Set the HP 432A range switch to coarse zero and adjust the front
panel coarse zero control to obtain a zero meter indication.
5. Fine zero the HP 432A on the most sensitive range, then set the
range switch to 1 mW.
Note
Ensure that the DVM input leads are isolated from chassis ground
when performing the next step.
6. Set up the DVM to measure microvolts.
7. Connect the positive and negative input leads, respectively, to the
V
comp
and V
RF
connectors on the rear panel of the HP 432A.
4402serv.book Page 8 Monday, March 11, 2002 11:34 AM