
Smoothing
Smoothing
(similar
to
video
ltering)
averages
the
formatted
active
channel
data
over
a
portion
of
the
displayed
trace
.
Smoothing
computes
each
displayed
data
point
based
on
one
sweep
only
,
using
a
moving
average
of
several
adjacent
data
points
for
the
current
sweep
.
The
smoothing
aperture
is
a
percent
of
the
swept
stimulus
span,
up
to
a
maximum
of
20%.
Rather
than
lowering
the
noise
oor
,
smoothing
nds
the
mid-value
of
the
data.
Use
it
to
reduce
relatively
small
peak-to-peak
noise
values
on
broadband
measured
data.
Use
a
suciently
high
number
of
display
points
to
avoid
misleading
results
.
Do
not
use
smoothing
for
measurements
of
high
resonance
devices
or
other
devices
with
wide
trace
variations
,
as
it
will
introduce
errors
into
the
measurement.
Smoothing
is
used
with
Cartesian
and
polar
display
formats
.
It
is
also
the
primary
way
to
control
the
group
delay
aperture
,
given
a
xed
frequency
span.
(Refer
to
\Group
Delay
Principles"
earlier
in
this
section.)
In
polar
display
format,
large
phase
shifts
over
the
smoothing
aperture
will
cause
shifts
in
amplitude
,
since
a
vector
average
is
being
computed.
Figure
6-25
illustrates
the
eect
of
smoothing
on
a
log
magnitude
format
trace
.
Figure
6-25.
Eect
of
Smoothing
on
a
Trace
IF
Bandwidth
Reduction
IF
bandwidth
reduction
lowers
the
noise
oor
by
digitally
reducing
the
receiver
input
bandwidth.
It
works
in
all
ratio
and
non-ratio
modes
.
It
has
an
advantage
over
averaging
as
it
reliably
lters
out
unwanted
responses
such
as
spurs
,
odd
harmonics
,
higher
frequency
spectral
noise
,
and
line-related
noise
.
Sweep-to-sweep
averaging,
however
,
is
better
at
ltering
out
very
low
frequency
noise
.
A
tenfold
reduction
in
IF
bandwidth
lowers
the
measurement
noise
oor
by
about
10
dB
.
Bandwidths
less
than
300
Hz
provide
better
harmonic
rejection
than
higher
bandwidths
.
Another
dierence
between
sweep-to-sweep
averaging
and
variable
IF
bandwidth
is
the
sweep
time
.
A
veraging
displays
the
rst
complete
trace
faster
but
takes
several
sweeps
to
reach
a
fully
averaged
trace
.
IF
bandwidth
reduction
lowers
the
noise
oor
in
one
sweep
,
but
the
sweep
time
may
be
slower
.
Figure
6-26
illustrates
the
dierence
in
noise
oor
between
a
trace
measured
with
a
3000
Hz
IF
bandwidth
and
with
a
10
Hz
IF
bandwidth.
Application
and
Operation
Concepts
6-45
Содержание HP 8753D
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