Agilent Technologies 8719D, User Manual

Page: 133 / 673

7. enter the relative velocity of the cable under test, press:
. . . .
and enter a velocity factor for your cable under test
Note
Most cables have a relative velocity of 0.66 (for polyethylene dielectrics) or 0.7
(for
PTFE
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 read the actual round trip distance to the reflection
of interest rather than the “electrical length” that assumes a relative velocity
of 1.
velocity factor
= where is the relative permittivity of the cable
dielectric
8. position the marker on the reflection of interest, press:
and turn the front panel knob or enter a value from the front panel keypad.
In this example, the velocity factor was set to one-half the actual value, so the marker reads
the time and distance to the reflection.
9.
position a marker at each reflection of interest, as shown in Figure 2-64, press:
. . . . . . . .
. . . . . . . . . . . .
,
front panel keypad after each key press.
Figure 2-64. Device Response in the Time Domain
M a k i n g M e a s u r e m e n t s