gEDA-user: Spice Transmission Line Simulation Question

[User Tomdean <tomdean@xxxxxxxxxxxxx>]

I am using Spice 3f5, attempting to model a coax line.  I am a nubie
at this.  The lossless example uses two lines to model one coax.  Do I
need to do this with the ltra model?  It does not seem to make a
difference.

I get funny results.  I use 

ac dec 100 1 1000meg
plot db(v(4)/v(2))

I see what I expect up to about 18mHz and then it oscillates.

What am I doing wrong?

tomdean

RG-8/U Simulation
* Z    L        C       V    TD     Rc           Rs            vswr    f
*      (uh/ft) (uf/ft) (%c) (ns/ft) (ohm/1000ft) (ohm/1000ft)          (mhz)
*50    .065    24.8    82   1.24    1.2          1.1           1.43:1  2250
*51.5  .059    22.5    85
* 10 ft line
.model inner LTRA (L=.065uh C=24.8pf R=.0012 len=10)
.model outer LTRA (L=.065uh C=24.8pf R=.0011 len=10)
.subckt rg8u_10 a1 a2 a3 a4
o1 a1  a2  a3  a4 inner
*o2 a2  0   a4  0  outer
.ends
*v1 1 0 0 c pulse 0 1 1ns 0.1ns
v1 1 0 dc 0 ac 1
r1 1 2 50
r2 4 0 50
X1 2 0 4 0 rg8u_10
* ac dec 100 1 1000meg
* plot db(v(4)/v(2))
.end


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