HP 8753D - Page 400

Gating
Gating
provides the
exibility
of
selectively
removing
time
domain
responses
.
The
remaining
time
domain responses
can
then
be
transformed
back
to
the
frequency
domain.
F
or
reection
(or
fault location)
measurements
,
use
this
feature
to
remove
the
eects
of
unwanted
discontinuities
in the
time
domain.
Y
ou
can
then
view
the
frequency
response
of
the
remaining
discontinuities
.In
a transmission
measurement,
you
can
remove
the
eects
of
multiple
transmission
paths
.
Figure
6-74
a
shows
the
frequency
response
of
an
electrical
airline
and
termination.
Figure
6-74
b
shows
the
response
in
the
time
domain.
The
discontinuity
on
the
left
is
due to
the
input
connector
.
The
discontinuity
on
the
right
is
due
to
the
termination.
W
e
want
to remove
the
eect
of
the
connector
so
that
we
can
see
the
frequency
response of
just the
airline and
termination.
Figure
6-74
c
shows
the
gate
applied
to
the
connector
discontinuity
. Figure
6-74d
shows
the
frequency
response
of
the
airline
and
termination,
with
the
connector
\gated out."
Figure 6-74.
Sequence of
Steps
in
Gating
Operation
Setting
the
gate
. Think
of a
gate as
a bandpass
lter
in
the
time
domain
(see
Figure
6-75
).
When
the
gate
is
on,
responses outside
the gate
are mathematically
removed
from
the
time
domain
trace
.
Enter
the
gate position
as a
start and
stop time
(not
frequency)
or
as
a
center
and
span
time
.
The
start and
stop times
are the
bandpass lter
0
6
dB
cuto
times
.
Gates
can
have
a
negative
span, in
which case
the responses
inside the
gate are
mathematically removed.
The
gate's start
and stop
ags dene
the region
where
gating
is
on
.
Application and Operation Concepts 6-133