Audio True Rms Detector And Notch Filter Gain - HP 8901B Operation And Calibration Manual

Model
8901B
Adjustments
Adjustment 21
AUDIO TRUE RMS DETECTOR AND NOTCH FILTER GAIN
Service Sheet 16
Description
The offset of the audio true
rms
detector is first adjusted to read zero with no audio input, then a
signal of known level is applied to the detector and the sensitivity of the detector is adjusted to read
the correct level. The gain of the audio notch filter is adjusted for a reading of 100% with an input
signal that is twice the frequency of the notch filter.
Equipment
Audio Oscillator
..................................................................
HP 8903B
Digital Voltmeter
.................................................................
H P 3455A
OUTPUT AUDIO OSCILLATOR
INPUT DIGITAL VOLTMETER
Figure
5-9.
Audio T h e RMS Detector and Notch Filter Gain Adjustment Test Setup
Procedure
1. Remove any cable from the MODULATION OUTPUT/AUDIO INPUT connector of the
Modulation Analyzer.
2. On the Modulation Analyzer, press the blue key then press INSTR PRESET (the AUTOMATIC
OPERATION key) to preset the instrument. Key in 30.0 SPCL to set the instrument to measure
and display the voltage at the MODULATION OUTPUT/AUDIO INPUT connector with the
audio true rms detector. Key in 49.7 SPCL to measure and display the output of the audio true rms
detector. (The displayed voltage will be ten times the level displayed with Special Function 30.)
3. Adjust A52R47 (RMS
OFS)
for a reading on the Modulation Analyzer's display between -0.0005
and 0.0005.
4. Key in 30.0 SPCL. The display should read 0.0000 V.
5. Connect the equipment as shown in Figure 5-9.
6. Set the audio oscillator for 3.9 Vrms into an open circuit at 2 kHz. Set the voltmeter to read
ac volts.
7. Adjust A52R38 (RMS
SENS)
for a reading on the display of the Modulation Analyzer that
is
the same as the reading on the voltmeter to the third decimal place. (The readings should be
approximately 3.9
Vrms.)
Adjustment 21
5-35