HP 8901B Operation And Calibration Manual page 206

Operation
Model 8901B
COMMENTS
Input/Output Status
When the tuned RF level measurement is selected, MODULATION OUTPUT/AUDIO INPUT is
blanked. AM OUTPUT and FM OUTPUT (rear panel) remain active during this measurement.
Relative Measurements
If the tuned RF level is to be displayed relative to a reference, enter the value as a ratio reference using
the RATIO key. (Refer to Ratio on page 3-215.)
3-92
Tuned RF Level