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Modulation and Audio
5-7
SlNAD
The HP 8902A allows you to make SINAD measurements (at 1 kHz or
400 Hz) on the internally
demodulated audio signal or on an external audio
signal applied to the MODULATION OUTPUT/AUDIO INPUT port.
Demodulated Audio
1 . Connect your modulated signal source to the HP 8902A's INPUT port.
2. Select the appropriate modulation mode (AM, FM or QM).
3. Key
in
29.0 SPCL, the Blue Shift key, and then the 1 kHz
DISTN (PEAK+) or 400 Hz DISTN (PEAK-) key. An annunciator
in the display indicates which frequency is being measured.
4.
Use the LOG/LIN key if you wish to toggle between
%
and dB units.
5. Press the appropriate Audio Filter keys to set the desired
measurement bandwidth for the internally demodulated audio signal.
External Audio
INPUT port on the HP 8902A.
6.
Connect your audio source to the MODULATION OUTPUT/AUDIO
7.
Press the AUDIO INPUT key (key should remain lit).
8.
Perform steps 3 and
4
above to measure the SINAD of the external
audio signal.
Signal-to-Noise
The HP 8902As Ratio Mode makes it easy to make relative measurements
such
as signal-to-noise on AM transmitters or hum and noise on
FM transmitters.
the modulation o f f .
or FM) and the RMS detector.
reference measurement.
1. Connect your signal source to the
INPUT
port on the HP 8902A and turn
2.
Select the appropriate modulation measurement on the HP 8902A, (AM,
3. Press the RATIO key to establish the unmodulated input signal as the
4.
Press the LOG/LIN key if you wish to toggle between
%
and dB units.
5. Turn on the modulation at the modulation source. The HP 8902A will
compute and display the signal-to-noise ratio.
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