The circuit simulator SPICE has built-in Lossless Transmission Lines (T),
Lossy Transmission Lines (O) and Uniform Distributed RC Lines (U) Model.
However both T and U model does not cosider frequency-dependent
conductor resistance. So it is not possible to calculate the transmossion
characteristic of the long cable.
This form generates adequate SPICE model for real taransmission line
of specfied attenuation and length.
The velocity raio is the ratio of the phase velocity of the electromagnetic
wave propergating througu the cable to the speed of light in vacuum.
This value is determined by the dielectric constant of cable
insulation as following relation.
Vr = 1 / sqrt(k)
Vr = velocity ratio (0 < Vr <= 1)
k = relative dielectric constant
= 2.3 (PE - Polyethylene insutation)
= 1.5 (CPE - Celler/foamed Polyethylene insutation)
= 2.1 (PTFE, PFA, FEP fluorocarbon polymer insulation)
= 1.0 (Aire insulation)
Frequency that defines the attenuation must be at several tens of MHz or higher.
The highest frequency of transmission signal spectrum is the
highest frequency limit of this SPIE model.
If this value is not sure, please be calculated by the following equation.
The highest frequency = 0.35 / the raise time of the pulse / 1e6 (MHz)
The precision of this model is about 2 % in the high accuracy model,
about 6 % in the statndard accuracy model,
about 12 % in the low accuracy model.
This model can apply wide range of transmission lines dielectric losses
are negligible in comparison with the conductor loss,
including coaxial cables, twin leads and strip lines.