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Model 8902A
Operation
SINAD
FUNCTIONS
1 kHz DISTN, 400 Hz DISTN, Special Function 29 (SINAD)
DESCRIPTION
Special Function 29.0 enables the Measuring Receiver t o make SINAD (Signal to Noise And Distor-
tion) measurements. T h e 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 o n audio signals with fundamental frequencies of either 1 kHz o r
400
Hz using the 1 kHz DISTN o r 400
Hz
DISTN keys respectively. T h e fundamental frequency must
be within f 5 Y o o f the nominal
1
kHz o r 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 o n 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 o n 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 o f the internally demodulated audio signal, select the desired
filter keys. (Refer t o
Airdio
Fi1lcv-s o n page 3-207.)
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-).
T h e measured results can be displayed in either linear units
( O h )
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
= A I
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
3-233
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