Email

Recipients email * (separate multiple addresses with commas)

Message *

 Send yourself a copy

Subscribe

Intro copy of the newsletter section here, some intro copy of the newsletter. Instruction of how to subscribe to this newsletter.

First Name *

Last Name *

Email *

Company / Institution *

 Send Yourself A Copy

PSpice: coax cable models

Last post Tue, Jul 23 2013 5:56 AM by alokt. 3 replies.
 Started by PavelM 21 Jul 2013 12:47 AM. Topic has 3 replies and 1450 views
• Sun, Jul 21 2013 12:47 AM

• PavelM
• Joined on Mon, Jun 1 2009
• Posts 2
• Points 40
PSpice: coax cable models
 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?SincerelyPavel
• Post Points: 20
• Mon, Jul 22 2013 6:18 AM

• alokt
• Joined on Fri, Aug 22 2008
• Posts 241
• Points 3,470
Re: PSpice: coax cable models
 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.
• Post Points: 20
• Mon, Jul 22 2013 7:32 AM

• PavelM
• Joined on Mon, Jun 1 2009
• Posts 2
• Points 40
Re: PSpice: coax cable models
 Hi, You've explained why there are two types of model for each coax cable.My question is different.Below is a model of RG58C/U from the TLine.lib file:********************************************************             Z0(Ohms)  vp(%)  F1(MHz) Loss1(dB/100Ft) F2(MHz)  Loss2(dB/100Ft)* RG58C/U        50       66      100       4.9      1000        20.model RG58C/U  TRN (r={63.9098u*sqrt(2*s)} l=252.700n+   g={0.1584230p*abs(s)}   c=101.08p)*\$* Subckt version uses fixed frequency, frq, to model simple lossy line**                  Near end hi*                   |  Near end lo*                   |   |  Far end hi*                   |   |   |  Far end lo*                   |   |   |   |.subckt RG58C/U    A1  A2  B1  B2 params: frq=100Meg len=1.param PI2 {3.141592654*2}*.model RG58C/U  TRN (r={63.9098u*sqrt(PI2*frq)} l=252.700n*+   g={0.1584230p*PI2*frq}   c=101.08p)t A1 A2 B1 B2 rg58c/u len={len}.ends*\$***********************************************In line 3 of the model above, one can find following definition of R: r={63.9098u*sqrt(2*s)} Why it is proportional to (2*s) and not to (s), as it should be for "simple" skin effect? What is a physical explanation of it? Where this coefficient 2 came from?ThanksSincerelyPavel
• Post Points: 20
• Tue, Jul 23 2013 5:56 AM

• alokt
• Joined on Fri, Aug 22 2008