External Leveling - HP 8340B Manual

4-6.
EXTERNAL LEVELING
Specification
Table
4-11. External Leveling Specifications
XTAL: Allows the HP 8340B/41B
to
be externally leveled by crystal detectors of positive or negative
polarity.
METER:
Allows power meter
leveling with any HP power meter-
Range (XTAL or METER): 500 microvolts
(-66
dBV) to 2.0 volts
(+6
dBV)
Accuracy of voltage at
EXT INPUT connector relative to the displayed level (leveling voltage is
shown
in
ENTRY DISPLAY
in
dBV):
±0.5
dB
±
200
microvolts.
Description
The HP 8340B/41B external leveling circuit
is designed to maintain
a
constant voltage at
the
EXT
INPUT
BNC. This
is
achieved by first
selecting
a
voltage
(in
dBV) to which the EXT
INPUT
will be
leveled. This establishes
a
reference voltage for the ALC. The
voltage at the EXT INPUT is
then routed
through the
external
leveling circuitry to the
ALC and compared to the reference. If
a
differnce
between the two voltages
exist, the HP
8340B/41B RF OUTPUT power
will be adjusted to compen¬
sate for the difference.
The HP 8340B/41B's external leveling circuit allows
a
positive or negative crystal detector to be used
in
the external leveling loop. A
negative crystal detector (HP
8473C)
is
used
in
this test but
a
crystal
detector may be
substituted.
The HP 8340B/41B XTAL Leveling
mode
is
selected to verify the instrument's external leveling specifi¬
cation.
Nine different dBV values, ranging from
+6 dBV
to
-66
dBV, are selected and the voltage
accuracy at the
EXT INPUT
is checked with
a
DVM.
HP 8340B/41B
UNDER TEST DIGITAL VOLTMETER
Figure 4-6. External Leveling Test Setup
"L
lOOOpF
CAPACITOR
HP 8340B/41B
Performance Tests
4-33