16
* Model parameter units are as follows:
* len: meters
* r: Ohms/meter
* l: Henries/meter
* g: Mhos/meter
* c: Farads/meter
*$
* Z0(Ohms) vp(%) F1(MHz) Loss1(dB/100Ft) F2(MHz) Loss2(dB/100Ft)
* RG6A/U 75 66 100 2.9 1000 11
.model RG6A/U TRN (r={59.5022u*sqrt(2*s)} l=379.050n
+ g={0.0428900p*abs(s)} c=67.3867p)
*$
An alternate version of the model is obtained by using the FREQ attribute on the RG6A/U part to use a
specified frequency to evaluate R and G. This can have some advantages in transient analysis.
* Subckt version uses fixed frequency, frq, to model simple lossy line
*
* Near end hi
* | Near end lo
* | | Far end hi
* | | | Far end lo
* | | | |
.subckt RG6A/U A1 A2 B1 B2 params: frq=100Meg len=1
.param PI2 {3.141592654*2}
.model RG6A/U TRN (r={59.5022u*sqrt(PI2*frq)} l=379.050n
+ g={0.0428900p*PI2*frq} c=67.3867p)
t A1 A2 B1 B2 rg6a/u len={len}
.ends
Modeling R and G at high frequencies
Attenuation vs. frequency data is generally available to ~1GHz for coax cable. At frequencies above
~1MHz, R and G have the following dependences on frequency:
Here is complex frequency (the Laplace variable).
Modeling Attenuation In Mathcad:
The following is a Mathcad program which fits the loss parameters R and G to two points of the
Attenuation vs. Frequency curve:
Enter attenuation of 100' of cable in dB at f1.
attn1 2.9
Enter characteristic impedance of cable.
Enter frequency @ attn1
f1
.
100 10
6
z0 75
Enter attenuation of 100' of cable in dB at f2.
attn2 11
s b G s a R
