HP 8901B Operation And Calibration Manual page 298

Model 8901B Operation
FUNCTIONS
1 kHz DISTN, 400 Hz DISTN, Special Function 29 (SINAD)
DESCRIPTION
Special Function 29.0 enables the Modulation Analyzer
to make SINAD (Signal to Noise And
Distortion) measurements. The SINAD measurement is identical
to
the audio distortion measurement;
but the result is expressed differently. SINAD is often measured as part of receiver sensitivity testing.
SINAD can be measured on audio signals with fundamental frequencies of either 1 kHz or 400 Hz using
the 1 kHz DISTN or 400 Hz DISTN keys respectively. The fundamental frequency must be within
&5% of the nominal
1
kHz or 400 Hz for accurate measurements. Once selected, the measurement
frequency remains unchanged and is automatically activated each time the SINAD (or audio distortion)
measurement is selected.
SINAD can also
be measured on an external audio signal applied to the MODULATION OUTPUT/
AUDIO INPUT connector using the AUDIO INPUT key. When external audio
is
not selected, the
instrument measures the SINAD on the internal demodulated audio.
PROCEDURE
To measure SINAD on the demodulated audio signal, select 29.0 SPCL.
To measure SINAD on an external audio signal applied to the MODULATION OUTPUT/AUDIO
INPUT, select 29.0 SPCL and AUDIO INPUT. (Only the true rms detector can be used for
this measurement.)
To change the measurement bandwidth of the internally demodulated audio signal, select the desired
filter keys. (Refer
to Audio Filters on page 3-179.)
If measurements are to be made on a
1
kHz signal, select 1 kHz DISTN (Blue Key, PEAK+). If
measurements are to be made on a 400 Hz audio signal, select 400 Hz DISTN (Blue Key, PEAK-).
The measured results can be displayed in either linear units (9%) or logarithmic units
(dB)
using the
LOG/LIN key. The previously selected units are reinstated whenever an audio measurement is selected.
HP-IB PROGRAM CODES
AUDIO INPUT = A1
MODULATION OUTPUT
=
A0
1 kHz DISTN =
D5
400 Hz DISTN = D6
LIN results = LN
LOG results = LG
SPCL = SP
MEASUREMENT TECHNIQUE
To measure SINAD, the instrument compares the input signal level measured
by a
true rms detector
to the same measurement with the fundamental component removed. SINAD is then calculated as the
ratio of the unfiltered signal to the signal with its fundamental removed. Refer
to
the measurement
technique discussions in Audio Distortion and
Level
on page 3-201.
SINAD 3-203