D. V
p
of Common Cables
D.1. Cable Types
Commonly encountered cable designations, along with their associated characteristic impedances
and typical Vp values, are listed below. A more complete listing is stored in the CT100B’s internal
memory. Note that the actual Vp of a given cable can vary by manufacturer, manufactured lot,
cable age and condition, whether it is flat or coiled on a roll, and other variables. The most
accurate way to test a cable is to determine the Vp of the cable using the CT100B and a known
length of the cable you wish to test. See Section 4.4 for more information on determining the Vp of
a cable.
D.2. Dielectric Material
Table D.1. Vp of Common Dielectric Materials
Type Probable Vp
Jelly-filled 0.64
Polyethylene 0.66
PTFE / TFE 0.70
Pulp 0.72
Foam / cellular PE 0.78
Semisolid PE 0.84
Air 0.98
CT100B TDR Cable Analyzers Operator’s Manual 123
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