Figure
6-75.
Gate
Shape
Selecting
gate
shape
.
The
four gate
shapes available
are listed
in T
able
6-12
.
Each
gate
has
a
dierent
passband
atness
,
cuto
rate,
and sidelobe
levels.
T
able
6-12.
Gate
Characteristics
Gate
Shape
P
assband
Ripple
Sidelobe
Levels
Cuto
Time
Minimum
Gate Span
Gate
Span
Minimum
6
0.10
dB
0
48
dB
1.4/Freq
Span
2.8/Freq
Span
Normal
6
0.01
dB
0
68
dB
2.8/Freq
Span
5.6/Freq
Span
Wide
6
0.01
dB
0
57
dB
4.4/Freq
Span
8.8/Freq
Span
Maximum
6
0.01
dB
0
70
dB
12.7/Freq
Span
25.4/Freq
Span
The
passband
ripple
and
sidelobe
levels
are descriptive
of
the
gate
shape
.
The
cuto
time
is
the
time
between
the
stop
time
(
0
6
dB on
the
lter
skirt)
and
the
peak
of
the
rst
sidelobe
,
and
is
equal
on
the
left
and
right side
skirts of
the
lter
.
Because
the
minimum
gate
span
has
no
passband,
it
is
just
twice
the
cuto time
. Always
choose
a
gate
span
wider
than
the
minimum.
For
most applications
,
do
not
be
concerned
about
the
minimum
gate
span,
simply
use
the
knob
to position
the gate
markers
around
the
desired
portion
of
the
time
domain
trace
.
Transforming
CW Time
Measurements Into
the
Frequency
Domain
The
analyzer can
display the
amplitude and
phase of
CW
signals
versus
time
.
F
or
example
,
use
this
mode
for
measurements
such
as
amplier
gain as
a
function
of
warm-up
time
(i.e
.
drift).
The analyzer can display the measured parameter (e
.g. amplier
gain) for periods of up to
24 hours and then output the data to a digital
plotter for hardcopy results
.
These \strip chart" plots are actually measurements as a function of time (time is the
independent variable), and the horizontal display axis is scaled in time units
. Transforms of
these measurements result in frequency domain data. Such transforms are called forward
transforms because the transform from time to frequency is a forward F
ourier transform, and
can be used to measure the spectral
content of a CW signal. F
or example, when transformed
into the frequency domain, a pure CW signal measured over time appears as a single frequency
spike. The transform into the frequency domain yields a display that looks similar to a
spectrum analyzer display of signal amplitude versus frequency.
6-134 Application and Operation Concepts
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