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?

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  • \$\begingroup\$ 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). \$\endgroup\$ Commented Aug 13, 2017 at 6:53
  • \$\begingroup\$ @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/… \$\endgroup\$
    – barryxian
    Commented Aug 14, 2017 at 14:12
  • \$\begingroup\$ It's in meters. If you want a one inch length, you would write 0.0254, or 25.4m (25m4 is also accepted). \$\endgroup\$ Commented Aug 15, 2017 at 6:07
  • \$\begingroup\$ @aconcernedcitizen, thank you so much for your kind help!! It helps a lot!!! \$\endgroup\$
    – barryxian
    Commented Aug 15, 2017 at 14:35

1 Answer 1


I'm not sure you can call a model TLINE but maybe you can. You should not enter units. Let's call the model 'myTline': .model myTline LTRA(R=10m L=9n C=3.59p len=1) R/L/C are parameters for a piece of wire of '1' length (if R/L/C values describe Ohms/Henries/Farads per meter then len of 1 is 1 meter). So if you want double the length you set it to 2 etc.

Then you just fill the 'Value' in LTRA component properties to be 'myTline', don't fill the other fields.


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