HP 8753D - Page 386

Time
Domain
Bandpass
This
mode
is
called
bandpass
because
it
works
with
band-limited
devices.
Traditional TDR
requires
that
the
test
device
be
able
to
operate down
to dc
.Using
bandpass mode
,there
are no
restrictions
on
the
measurement
frequency
range
.
Bandpass
mode characterizes
the test
device
impulse
response
.
A
djusting
the
Relative
V
elocity
F
actor
A
marker
provides
both
the
time
(x2)
and
the electrical
length (x2)
to a
discontinuity
.
T
o
determine
the
physical
length,
rather
than
the
electrical
length, change
the velocity
factor to
that
of
the
medium
under
test:
1.
Press
4
CAL
5
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N
VELOCITY
FACTOR
.
2. Enter
a velocity
factor between
0
and
1.0
(1.0
corresponds
to
the
speed
of
light
in
a
vacuum). Most
cables have
a velocity
factor
of
0.66
(polyethylene
dielectrics)
or
0.70
(teon
dielectrics).
Note
T
o
cause
the
markers
to
read
the
actual
one-way
distance
to
a
discontinuity
,
rather
than
the
two-way
distance
,
enter
one-half
the
actual
velocity
factor
.
Reection
Measurements
Using
Bandpass
Mode
The
bandpass
mode
can
transform
reection
measurements
to
the
time
domain.
Figure
6-62
a
shows
a
typical
frequency
response
reection
measurement
of
two
sections
of
cable
.
Figure
6-62
b
shows
the
same
two
sections
of
cable
in the
time
domain
using
the
bandpass
mode
.
Application and Operation Concepts 6-119