Sweep (16 - HP 8340B Manual

Accuracy
NOTE: An HP 8340B with option 001 or 005 does not have
a
step attenuator.
Flatness
is
adjusted and tested with the RF output power
at
0
dBm (RF attenuator at
0 dB
and
ALC
at
0
dBm). The frequency response normally remains the same over the ALC range. For accuracy
prob¬
lems within the ALC range, refer to the ALC adjustments
in
Section V, Adjustments, and to the
RF
section functional group
if
necessary.
If
accuracy
is within specifications over the ALC
range, and out
of
specifications
below the ALC range,
the problems
is
probably associated with the RF attenuator. Note that the RF attenuator
is outside of
the ALC Loop.
The
instrument processor programs the RF attenuator, but there
is
no way
for the
processor
to know
if
the attenuator actually stepped properly. If
the power
level
is off by
a
factor of 10
dB, the attenuator may not be responding properly.
1.
Select
a
CW
frequency.
2.
Set the power
level to 0
dBM.
3.
Press [SHIFT] [PWR SWP].
ATN:
-00
dB. ALC: 0.00 dBm appears
in
the ENTRY display.
4.
Using the step keys, step the RF attenuator (and RF power
output) to —90 dB.
The attenuator should click at
each step, and the RF power should decrease
in
10 dB steps. If
the
attenuator does not perform properly, refer to
the
RF
section functional group.
5.
There is
an offset and slope calibration constant correction factor for each RF attenuator step
from
10 to 90 dB. A
printed
copy of values generated
at the last calibration should be located
inside the instrument (see pocket along left side rail). Check the calibration constants in
instru¬
ment memory against the
printed
copy values
and
restore the correct values,
if
necessary (see
HOW TO RESTORE FACTORY OPTIMIZED CALIBRATION CONSTANTS).
6.
If
the attenuator
is
operating properly and the calibration constants are correct, check the RF
connections from the A10 directional coupler
to
the RF attenuator
and
measure the power
accuracy at the attenuator output.
SWEEP (16)
1.
Make sure nothing is connected to the
rear panel stop sweep connector.
NOTE: Before performing the following steps, use the
SHIFT M4
diagnostic test to help isolate the
cause of
a sweep problem.
For sweep problems, refer to
the
sweep generator
—
YO
loop functional group troubleshooting. Use
the following information to further define the symptom.
The
following
steps assume the instrument works properly
in CW mode (no UNLK
indication).
A-44
Assembly-Level Service Overall Instrument Troubleshooting
HP 8340B/41B