Model 8901B Operation
Filter Characteristics
The individual filter characteristics are given below. The
3
dB
bandwidth
is
specified
in
the filter’s
designation and
is
typically accurate
to
f3%.
High-Pass Filters:
50 Hz High
Pass:
Two-pole Butterworth,
1%
flat
to
<200
Hz
300
Hz High
Pass:
Two-pole Butterworth,
1%
flat
to
<1
kHz
Low-Pass Filters:
3
kHz Low
Pass:
Five-pole Butterworth,
1%
flat
to
>1
kHz
15 kHz Low
Pass:
Five-pole Chebyshev,
1%
flat
to
>10 kHz
>20
kHz Low
Pass:
Nine-pole Bessel,
1%
flat
to
>10 kHz. (When used with square
wave modulation, this filter typically overshoots
<1%.
This filter’s
3
dB
point
is
typically
110 kHz.)
Filter Selection Does Not Affect Some Measurements
External Audio level, distortion, and SINAD measurements
are
unaffected by the audio filters.
Recommended Filter Selection
Because
of
the high sensitivity
of
the QM measurement
to
low-frequency audio (microphonics, hum,
etc.), use
of
the 50 Hz or
300
Hz low-pass filter
is
recommended. (Neither
is
switched in automatically.)
Audio
Filters
3-181
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