# LTspice, how to model a TLine

I am trying to do a simulation for a transmission line, I can draw below example circuit but got below two questions.

1. How to do this step: .model TLine LTRA(...)

It looks to define the component property and should I do it in "component attribute editor" but it doesn't work.

1. The 50 ohms impedance is based on the calculation SQRT(L/C), there is no column to specify this value, right?

• Press 'S' and add the SPICE directive .model MyLtline ltline L=<...> C=<...> len=<...> etc (as needed, L, C and len should be minimum) and place it in your schematic. For this you'll have to modify ltline with MyLtline (case insensitive). – a concerned citizen Aug 13 '17 at 6:53
• @aconcernedcitizen, thank you and it works now! btw, may I know what is the unit for LEN (inch??)? I google and found the units for RLCG but not LEN. Thank you! techdocs.altium.com/display/AMSE/… – barryxian Aug 14 '17 at 14:12
• It's in meters. If you want a one inch length, you would write 0.0254, or 25.4m (25m4 is also accepted). – a concerned citizen Aug 15 '17 at 6:07
• @aconcernedcitizen, thank you so much for your kind help!! It helps a lot!!! – barryxian Aug 15 '17 at 14:35