HP 8901B Operation And Calibration Manual page 243

Operation
Model 8901B
EXAMPLE
To measure the positive peak AM depth of a signal in a 50 Hz to 15 kHz demodulated signal bandwidth
LOCAL
(keystrokes)
(program codes)
M1
D1
H1L2
Detector
Measurement
2l-X
Filters
HP-IB PROGRAM CODES
All HP-IB codes for setting a limit or a specific display resolution for modulation-depth measurements
are provided in "Procedures".
AM
= M1
SPCL =
SP
MEASUREMENT TECHNIQUE
The AM Demodulator measures AM as a ratio of the demodulated audio signal level
to
the average
tuned carrier level. An automatic level control (ALC) loop within the AM Demodulator holds the carrier
level constant so
that
the percent
AM
is proportional
to
the peak amplitude of the demodulated audio
output. This audio output is then filtered, audio detected, and displayed as
' % I AM. The demodulated
AM is available at MODULATION OUTPUT/AUDIO INPUT (unless AUDIO INPUT is selected).
I
AM
I
7 DEMODULATOR\ AUDIO AUDIO VOLTMETER
(ALC LOOP)
FILTERS DETECT0 RS AN0 DISPLAY
INPUT
ATTENUATOR
IF
AMP
\' N PUTI
-
L
I
AM Measurement Block Diagram
3-136
AM