Agilent Technologies 8719ES User Manual page 194

Making Time Domain Measurements
Making Reflection Response Measurements
Figure 3-8 Device Response in the Frequency Domain
5. To transform the data from the frequency domain to the time domain, press:
System TRANSFORM MENU
6. To view the time domain over the length (<4 meters) of the cable under test, press:
LIN MAG
Format
Start 0 x1
Stop 35 G/n
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.
7. To enter the relative velocity of the cable under test, press
VELOCITY FACTOR
Most cables have a relative velocity of 0.66 (for polyethylene dielectrics) or 0.7
NOTE
(for teflon dielectrics). If you would like the markers to read actual one-way
distance rather than return trip distance, enter one-half the actual velocity
factor. Then the markers will read the actual one-way distance to the
reflection of interest rather than the "electrical length" that assumes a
relative velocity of 1.
Velocity Factor
where ε
3-10
BANDPASS
and enter a velocity factor for your cable under test.
1
= --------
ε
r
is the relative permittivity of the cable dielectric.
r
TRANSFORM ON
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Cal