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SECTION3
Service Innfomtion
AM Balance
8. Repeat stens 2 through 7 three or four limes until
boih the A?M balance"md AM offset reading limits
stated in steps 5 and 7 are satisfied.
1. Connect a Model 197A DMM to FCTN OUT, and
connect a second Model 3930A to the AM IN jack of
the Model 3930A being calibrated (see Figure 3-5).
The second Model 3930A will be used to provide an
amplitude modulation signal.
NOTE
Connect an oscilloscope, if one is available, in
parallel with the Model 197A input terminals
in order to make adjustments easier.
2. Set the DMM to the ACV function, and select auto-
ranging.
3. Setup the Model 3930A used for the AM signal as fol-
lows:
Factory Default (press SHIFT PRST)
Ah4rlD
2vp-p
4. Setup the Model 3930A being calibrated as follows:
Factory Default (press SHiFT PRST)
SOURCE: EXT %
MODE: GATE
AMPTD: 7.49vp-p
AMzON
5. Adjust R207 (AM BAL) so that the muliimeter indi-
cates 1OmV or less. (If an oscilloscope is being used,
adjust for minimum signal amplitude.)
6. Select the DCV function on the DMM.
7. Adjust R208 (AM OFS) for a DMM reading of OV +
AMGain
1. Disconnect the second Model 3930A from ,the AM IN
connector, and make sure the DMM is still connected
to the FCTN OTJT jack of the Model 3930A being cali-
brated (Figure 3-4).
2. Select the DCV function and auto-ranging on the
DMM.
3. Setup the Model 3930A as follows:
PHASE: -90"
4. Adjust R203 (AM GAIN) for a DMM reading of
-1.872V f 0.009V.
AM Offset
1. Connect the Model 197A DMM to FCTN OUT
(Figure 3-4).
2. Select the DCV function and auto-ranging on the
DMM.
3. Setup the Modd 3930A as follows:
PHASE 0"
4. Adjust R208 (AM OFS) for a DMM reading of OV f
2omv.
1ch.nv.
Model 3930A For AM Signal
Model 3930A Belng Callbrated
Pomona 1468
BNC-Banana
Model 197A DMM
u---------y
1
/
' cozdal cable
Function
output
Figure 3-5.
Second Mbdel393OA Connections
3-7
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