UTD2000M
User
Manual
Vertical
Coordinate
Linear/dBv
Set
the
unit
of
vertical
coordinate
to
be
linear
or
dBv
Select
FFT
Window
Based
on
the
assumption
that
YT
waveform
is
being
repeated
constantly,
the
oscilloscope
will
conduct
FFT
transformation
over
the
limited
time
record.
When
the
cycle
is
an
integer,
the
amplitudes
for
YT
waveform
at
the
beginning
and
in
the
end
are
identical,
so
the
waveform
will
not
be
interrupted.
However,
if
the
cycle
of
YT
waveform
is
a
non
‐
integer,
it
will
result
in
different
amplitudes
for
waveform
at
the
beginning
and
in
the
end,
thus
to
cause
high
frequency
transient
interruption
at
the
joint.
In
frequency
domain,
this
effect
is
called
a
leakage.
Therefore,
in
order
to
prevent
leakage
from
happening,
we
multiply
the
original
waveform
by
a
window
function
so
as
to
force
the
value
at
the
beginning
and
in
the
end
to
be
zero.
Refer
to
the
following
table
for
the
application
of
window
function.
Table
2
‐
4:
FFT
Window
Selection
FFT
Window
Feature
Most
Suitable
Measuring
Content
Rectangle
Best
frequency
resolution
and
worst
amplitude
resolution.
Basically
similar
to
the
condition
without
window.
Transient
state
or
short
pulse
and
the
signal
level
remains
more
or
less
the
same
before
and
after
this.
Constant
amplitude
sinusoid
with
extremely
close
frequency
has
wide
bandwidth
random
noise
that
has
relatively
slow
‐
changing
spectrum.
Hanning
Hamming
In
comparison
to
rectangle
window,
it
has
relatively
good
frequency
resolution
and
relatively
bad
amplitude
resolution.
Hamming
Hanning
The
frequency
resolution
of
Hamming
window
is
a
bit
better
than
that
of
Hanning
window.
Sine,
cycle
and
narrow
band
random
noise
Transient
state
or
short
pulse
with
signal
level
varies
widely
before
and
after
this.
Blackman
Best
amplitude
resolution
and
worst
frequency
resolution.
Mainly
used
for
single
frequency
signal
and
for
searching
higher
sub
‐
harmonic
FFT
Operation
Skills
.
A
signal
with
DC
component
or
bias
may
result
in
wrong
or
biased
waveform
component
analysis
using
FFT.
To
reduce
DC
component,
AC
coupling
mode
may
be
selected.
Also
to
reduce
random
noise
caused
by
repeat
or
single
pulse
incident
and
aliasing
frequency
component,
the
signal
acquiring
mode
of
digital
storage
oscilloscope
can
then
be
set
as
“averaged
acquiring”.
29
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