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Service Procedures 181
Appendix D
Modulation Adjustment
The function generator stores three calibration constants related to amplitude
modulation depth. The constants are calculated from the adjustment value
entered. If the calibration procedure is aborted before all setup steps have
been completed, no calibration constants are stored.
1. Use a DMM to measure the function generator ACrms output voltage
for SETUP 30 in the following table. These adjustments use a HIGH
Z output termination.
2. Send the CAL:VALue <measured Vac> to the function generator.
3. Send the CAL? command to the function generator to initiate the
calibration.
4. Repeat steps 1, 2 and 3 for SETUP 31 through 32.
5. Perform the “AM Modulation Depth Verification” on page 172.
Note NEW CALIBRATION: A new calibration (SETUP 85 – Rev 4.0) has been
added to eliminate a small residual error in the AM amplitude system which
could potentially cause a failure of the AM amplitude verification.
The new calibration operates just like the other AM calibrations (SETUP
30, 31, 32) in that the external measurement is AC Vrms with no load. The
new calibration is not allowed until the other AM gain calibrations (SETUP
30, 31, 32) are performed.
The new algorithm is designed such that the calibration should not be
required again once the function generator has been calibrated at the
factory. However, if you change any critical analog components which
determine amplitude in AM modulation, you should perform the calibration
again.
Table D-14. Modulation Adjustment Setups
Nominal Output
SETUP FREQUENCY AMPLITUDE Adjustment for:
30 1 kHz 3.5 Vrms 0% modulation depth.
31 1 kHz 0.707 Vrms 50% modulation depth.
32 1 kHz 6.36 Vrms 100% modulation depth.