Re: gEDA-user: Spice Transmission Line Simulation Question

[User Tomdean <tomdean@xxxxxxxxxxxxx>]

Thanks for the replies.

I have not looked into this type analysis for some 20 years.  I still
have my Terman reference!

The value/unit is specified in the Spice 3f5 help pages.

I used the value/foot specifications for Belden 9914 Coax and
specified the length in feet.  I added the center conductor and shield
resistances.

.model rg_8u LTRA (len=3.2808399 l=.065uh c=24.8pf r=2.3))
v1 1 0 dc 0 pulse 0 1 1ns 0.1ns
tran 1p 15n

I see v(1) starting to rise at 1.010000e-09 and v(3) starting to rise
at 5.204000e-09 sec or a transmission time of 4.194000e-09 seconds.
The length is 1 meter.

    1/4.194000e-09 = 2.384359e+08 meters/sec or 79.4% C (3e8) 
        JPL in DE405 gives 2.9979245799999998E+08.
    4.194000e-09/3.2808399 = 1.278E-09 sec/ft delay.

The spec sheet says velocity of propagation 82% and nominal delay
1.24ns/ft.

v1 1 0 dc 0 ac 1 sin 0 1e6
ac lin 1e4 1e8 1e9
plot 10*log((v(3)*o1#i2)/(v(2)*o1#i1))

The ripple I see in the 300 to 900mHz area of the plot is 60mHz.  
This agrees with the specs.

The .02db ripple amplitude.  How do I calculate this?

ac lin 1e5 1 1e9
plot 10*log((v(3)*o1#i2)/(v(2)*o1#i1))

The losses do not agree with the mfg datasheet.

tomdean


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