HP 85027A/B/C Adjustments
5.
On the back of the bridge is a printed, self-adhesive plastic label with a note that
explains the switch configuration. Remove the label. (Note: additional labels may
be ordered as P/N 8 5027-80004.)
6.
Disconnect the powei- sensor from the attenuator. Turn on the modulation (note:
the modulation frequency must be correct). Connect the input port of the bridge
to the attenuator. Leave the test port open.
7.
On the HP 8757A or 8756A, turn on the averaging (8, default factor) and cursor.
On the also HP 8757A turn on the smoothing (5%, default factor).
8.
Adjust the bridge’s gain potentiometer (R5) for a cursor reading of -6 ±0.1dBm.
9.
Set the attenuator for 30 dB. Adjust the bridge’s load potentiometer (R29) for a
cursor reading of calibrated -30 dB minus 6±0.1dBm.
10.
Set the attenuator to 0 dB and i-eadjust the gain potentiometer (if required) until
the cursor indicates -6 ±0.1dBm.
11.
Repeat steps 8 through 10 until the change in level is equal to the calibrated 30 dB
±0.1dB and the cursor with 0 dB attenuation indicates -6±0.ldBm.
DC Adjustment Procedure
NOTE
This DC procedure can be performed only with an HP 8757A
analyzer.
12.
Set the HP 8757A to DC mode.
13.
Set the analyzer’s reference level to -50 dBm at midscreen with a scale of 5
dB/division.
14.
Turn off the RF power from the source.
15.
Configure the system by pressing [CAL] [CONFIG SYSTEM] on the analyzer.
16.
On the bi-idge, temporarily short pad “Y” (where the yellow wire terminates) to
ground with a short jumper.
17.
Adjust the bridge Offset potentiometer (R25) for a minimum I-eading on the
analyzer. It should be less than -50 dBm.
18.
Remove the short completely.
Feedthru Null Adjustment Procedure
19.
Press [SYS] [CAL] [DC DET ZERO] [AUTOZERO] on the HP 8757A. Note that
for the AUTOZERO feature to function, the analyzer and source must be
connected through the System Interface.
20.
Adjust the bridge “feedthru null” potentiometer (RiO) for as HIGH a trace as
possible. Work slowly as the averaging and smoothing features will mask the
effects of your adjustments.
5-3
