[TowerTalk] Simulation of Mismatched Antennas

[Eric Gustafson]

>From: leewells@lexmark.com
>Date: Tue, 1 Sep 1998 14:43:13 -0400
>
>At K5GW's recommendation, I wrote a little program to simulate
>line loss, reflections, etc.  The program will print a line each
>time the wave travels the length of the line.  It displays the
>amount of power lost in the line, and absorbed by the load.
>Below are a couple of runs using Steve Best's numbers from his
>experiments.  The end values are almost identical.  If anyone
>wants the C source code, let me know and I can provide it.
>
>The programs assumes 100% of the power is reflected at the tuner
>end.  The reflected power at the antenna is a function of SWR:
>
>power refl coeff = ((SWR-1)/(SWR+1))^2
>	
>
>	73 
>	--Lee - KT4ZX

Snip...  (specific examples)

Hi Lee,

So did I.  But I just put the one pass formula from Maxwell's
book into a 30ish step program for my HP41C calculator.

I get the same numbers you do and that Steve did for the same
initial conditions.  I also verified the graphs in the ARRL
Handbook section on this subject.  Now that I have my calculator
all programmed up, I no longer need to do any interpolation or
extraolation from the graphs.

So, even though the methods are different, it looks like
everyone's calculations are giving valid results.

Out of all this discussion I have distilled a few truisms and
one false statement.  In the following, "system" refers to the
combination of feedline and antenna.

1.  When using lossy feedline, the higher the SWR is the lossier
    the system is.

2.  When using extremely low loss feedline, the higher the SWR
    is, the more loss the system has.

3.  It is always better to operate a particular antenna at low
    SWR beacuse SWR in and of itself independent of other system
    parameters causes increased system losses.

4.  When using lossless feedline, the system losses are
    independent of the SWR presented to the feedline by the load.

Statement 1, 2, and 4 are true.  Statement 3 is false.  If it was
true, then 4 would have to be false.  It was statement 3 (or one
very similar intended to imply the same thing) that some of us
took issue with.

73, Eric  N7CL

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