HP 8901B Operation And Calibration Manual page 275

Operation Model 8901B
PROCEDURE
When a modulation measurement is selected, a detector is automatically activated.
To obtain a peak detector, select either PEAK+ or PEAK-. Press both keys simultaneously to enable
the peak-average (PEAKf/2) mode.
Peak hold is used only with the peak detectors. Selecting PEAK
HOLD
initiates the peak hold mode.
To initiate another peak hold, press that key again. The display is now updated with the new peak.
The peak hold feature does not operate in the peak-average mode.
To obtain the average-responding, rms-calibrated detector, select AVG.
To initiate the true rms measurement, select RMS (Blue Key, AVG). The true rms detector is
selected automatically for the external audio level measurement (Special F'unction 3 0 ) , audio distortion
measurement, and SINAD measurement (Special Function 29).
HP-IB PROGRAM CODES
Function
PEAK+
PEAK-
PEAK HOLD
AVG
RMS
PEAK212
Program Code
D1
D2
D3
D4
D8
D9
Input/Output Status
The signal
at
MODULATION OUTPUT/AUDIO INPUT, AM OUTPUT, or FM OUTPUT is not
affected by the DETECTOR keys.
True RMS Detector
Only the true rms detector can be used for external audio level (Special h c t i o n
30)
and for audio
distortion measurement, and SINAD (Special k c t i o n 29.)
HP-IB Automatic Selection of Pre-Display
When the true
rms
detector is selected, the pre-display mode for
FM
de-emphasis is automatically
enabled. This is true whether FM has been selected or not. (Selection of the FM de-emphasis time
constant, however, remains unaffected.) The pre-display mode remains enabled until deliberately
disabled. This idiosyncrasy is important
to
remember when programming the instrument
via
HP-IB.
Peak Detector's Response Time
A
slower response time for the audio peak detectors can be selected with Special hnction
5 . 1 .
(Refer
to Audio Detector Response on page 3-177.)
3-174
Audio Detectors