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PSpice: coax cable models

PavelM

Hello,

As far as I've checked, coax cable models in PSpice (TLine.lib library file, which could be open in any ASCII editor) have some definition which looks strange for me. At least, I don't understand where it came from. For example, for RG58C/U coax cable, for its both .model and .subckt options the model series resistance is defined as "r={63.9098u*sqrt(2*s)}". This resistance is intended to model the skin effect losses, which is proportional to sqrt(s).

Later on in the model we can find the commented line with following "r={63.9098u*sqrt(PI2*frq)}". Here it is proportional to sqrt(2*pi*freq), which is a sqrt(s).

Exactly the same file exists in the pre-ORCAD version - MSim.

My question is why it is proportional to sqrt(2*s) in the active model and not to sqrt(s)? Where this factor 2 came from - mathematically / physically?

Sincerely

Pavel

Parents

  • In tline library, each co-axial cable (RG58C/U) has two simulation model implementation

    One in form of .Model and other in form of .SUBCKT, which uses fixed frequency for model. depending upon how instance parameters in your schematic, one of these model implementation would be picked up.

    In both case R is function of SQRT(Frequency); i.e you should get similar attenuation/phase shift for both of these and both of these are active models.

    Hope this clarifies.

Reply

  • In tline library, each co-axial cable (RG58C/U) has two simulation model implementation

    One in form of .Model and other in form of .SUBCKT, which uses fixed frequency for model. depending upon how instance parameters in your schematic, one of these model implementation would be picked up.

    In both case R is function of SQRT(Frequency); i.e you should get similar attenuation/phase shift for both of these and both of these are active models.

    Hope this clarifies.

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