Greetings colleagues. 

I have a transmission line model that has been very useful for me.  Maybe it will be useful to you.

I have upload Roy's OPM Transmission Line.zip for your perusal.  It includes a symbol and sub-circuit file foe a transmission line with frequency dependent skin effect and dielectric absorption.  It is differential mode only; it is an open circuit to common mode.  I find that it reproduces the data sheet attenuation of a variety of coaxial cables. It seems to be a good model for good transmission lines.  It might not be so great for waterlogged pulp insulated telephone cable.  It is a wide band model.  It works for any length of transmission line.  It can be used with both AC and transient analysis. It does use Laplace elements, but it seems well behaved in my use.  It is based mostly on the secondary line parameters (impedance, velocity, loss).

There are several numbered examples.  They may make most sense if examined in numerical order.

I also include 4 gaussian pulse sources that work for both transient and AC analysis.  Internally, each source has two sources that add.  One source only produces output during transient analysis and the other only during AC analysis.  The AC source uses a Laplace Transform element such that if you view the output of the AC source using the FFT option, you will see the same time domain response as the transient source.

All rights to the files uploaded in that zip file are released under Creative Commons Attribution 4.0 (CC BY 4.0).  To me that means that you can do whatever you want with these files if you give me attribution and you do not create any liability for me.

If you have problems with the model, it is probably better to email me directly instead of cluttering up the group.