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Date: Tue, 21 Feb 2012 14:56:24 -0800
From: Traylor Roger  <traylor AT eecs DOT oregonstate DOT edu>
To: geda-user AT delorie DOT com
Subject: [geda-user] LTRA vs TXL t-line model in ngspice
Message-ID: <20120221225624.GA23133@slana.eecs.oregonstate.edu>
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Reply-To: geda-user AT delorie DOT com

Gang,
 I have a netlist with two different t-lines.  One uses
 the TXL model, the other the LTRA model. Both are lossy.
 I am modeling RG-58 coax.  I sweep frequencies from 1Mhz
 to 1Ghz.  

 When using the LTRA model, everything works.  I have the
 0.3 meter length of cable shorted at the far end and see
 nice standing waves.

 When using the TXL model, the input to the cable looks like
 50ohms, but there are no standing waves.

 Any ideas?  Netlist follows.

 Thanks,
 Roger Traylor

--------------------------------------------------------

Simple T line with standing waves 

Vin vin 0 dc 0.0 ac 1.0 sin(0 1.0) 
Rsrc vin t1_in 50

try the TXL model
*y1 t1_in 0 t1_out 0 ymodel LEN=0.3
*.MODEL ymodel txl R=0.035 L=252n G=0 C=102.4p length=0.3

*try the LTRA model
O1 t1_in 0 t1_out 0 LOSSYMOD
.MODEL LOSSYMOD LTRA R=0.035 L=252n G=0 C=102.4p len=0.3

rload  t1_out  0 0.1 

.control
  ac lin 100000 1Meg 1000Meg
  plot vm(t1_in)  vm(t1_out)  vm(vin)
.endc

.end