EXFO CableSHARK P3 VF/DSL Cable Qualifier User Manual
Page 94
VF / DSL Cable Qualifier
82
Polypropylene
VOP = 0.66 (99 m/
μs)
Teflon
VOP = 0.67 (100 m/
μs
Pulse Width Vs. Test Distance
Assuming a V.O.P. of 66%
Pulse
Width
Maximum
Range
100 ns 50 ft / 16 m to 2000 ft / 660 m
1
μs 400 ft / 120 m to 6000 ft / 2000 m
6
μs 1850 ft / 560 m to 16000 ft / 4850 m
Calculating the Correct VOP
The exact VOP of a cable of known-length can be determined with the CableSHARK by running a successful
TDR test and reading the time (in ns) between the sent pulse and the reflection pulse from the end of the
cable, regardless of whatever the VOP setting is for the TDR test. Then, the exact VOP of the cable can be
calculated as:
Metric Calculation
VOP = cable length (m) / time reading (s) / light speed / 2
Where the speed of light is 299792458 m/s
Imperial Calculation
VOP = cable length (ft) / time reading (s) / light speed / 2
Where the speed of light is 983559096 ft/s
The division by 2 is due to the return trip that the pulse has traveled.
Determining the Correct VOP
Given a cable of known length, users can determine the correct VOP of that cable. By manually adjusting the
VOP, users can test from both ends of the cable until the CableSHARK measures the exact length of the
cable.