simple electric characteristics computation
Frequentry used electrical characteristics of wire and cable is as follows.
The resistance, capacitance, inductance and conductance are called primary
parameters, and used for low frequency applications. The characteristic
impedance, velocity ratio (phase constant) and attenuation are called
secondary parameters and used for high frequency applications.
These characteristics is analytically computable at only very simple
constructions. We must usr numerical method for complex structue.
But values for these basic constructions are usefull for proximation
at many cases.
- The resistance of cable varies largely with frequency because of
skin effect and proximity effect of conductor.
(use "wire-gauge calculation" for DC-resistance.)
- The capacitance of cable depends on geometrical structure and
dielectric constant of insulation material. The dielectric
constant varies with frequency and temperature, but for
poly-ethylene and poly-popylene and tetra-furuolo-ethylene,
it is almost independent of frequency and temperature. The
dielectric constant of PVC varies largely with temperature,
frequency and construction of compound.
- The inductance of cable depends on geometrical structure and permiability
of conductor and insulation material. But its value for cable is
very small as other electrical parts, it is neglectable for most of
- The conductance of cable depends on insulation registance at DC,
buf it depends on dielectrical loss at high freqency.
- The characteristic impedance varies largely with frequency at low
frequency range. But it is almost constant at high frequency range
about few MHz and higher.
- The velocity ratio of cable depends on dielectric constant of
- The attenuation constant of cable depends on conductor resistance
and dielectric loss of insulation. At lower frequency range as
lower than about 1 GHz, dielectric loss is negligible.