Modulation and Audio
5-7
S/NAD
The
HP
8901B
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 8901B’s INPUT port.
2.
Select the appropriate modulation mode (AM,
FM
or
@M).
3.
Key in
29.0
SPCL,
the
Blue
Shift
key, and then the
1
kHr
DlSTN (PEAK+)
or
400
Hs
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
8901B.
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-fo-Noise
The HP
8901B’s
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
off.
or
FM)
and the
RMS
detector.
reference measurement.
1.
Connect your signal source to the INPUT port on the
HP
8901B and
turn
2.
Select the appropriate modulation measurement on the HP 8901B,
(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
8901B
will
compute and display the signal-to-noise ratio.
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