HP 8753D - Page 123

4. T
o better
view the
measurement trace
, press:
4
SCALE
REF
5
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AUTO
SCALE
Figure
2-55
shows
the
frequency
domain
reection
response
of
the cables
under test.
The
complex
ripple
pattern
is
caused
by
reections
from
the
adapters interacting
with each
other
.
By
transforming
this
data
to
the
time
domain, you
can determine
the magnitude
of
the
reections
versus
distance
along
the
cable
.
Figure
2-55.
Device
Response
in
the
Frequency
Domain
5.
T
o
transform
the
data
from
the
frequency
domain
to
the
time domain,
press:
4
SYSTEM
5
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TRANSFORM
MENU
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BANDPASS
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TRANSFORM
ON
6.
To
view
the
time
domain
over
the
length
(
<
4
meters)
of
the
cable
under
test,
press:
4
F
ORMA
T
5
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NN
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LIN
MAG
4
ST
ART
5
4
0
5
4
x1
5
4
STOP
5
4
35
5
4
G/n
5
The
stop
time
corresponds to
the length
of the
cable under
test.
The
energy
travels
about
1
foot
per
nanosecond, or
0.3 meter/ns
,in
free space
.
Most
cables
have
a
relative
velocity
of
about
0.66 the
speed in
free space
. Calculate
about 3
ns/foot, or
10
ns/meter
,
for
the
stop
time when
you
are
measuring
the
return
trip
distance
to
the
cable
end.
2-74 Making Measurements