[TowerTalk] 160m shunt feed followup

[alsopb]

Tom Rauch wrote:
>
> 
> Since Z is scalar unless you can sort out the real and imaginary
> parts, you have no idea what you are measuring.
> 
> 

You can back out the value of X using the SWR and value of Z.

The formula is in the AUTEK manual.  The sign of it is easy to
determine.
First find the resonant freq.  If your freq of interest is higher then
the sign of Z is + (inductive) and vice versa.  To get practice, try
this first on a simple antenna with well known characteristics.  Take
about 5 points either side of resonance and plot the R and X values. 
It will be pretty obvious when X changes signs.

The following is a basic program (assuming 52 ohm line) for computing
X and R.

5 CLS
10 INPUT "Z=",Z
20 INPUT"SWR=",SWR
30 R =(2704+Z*Z)*SWR/(52*(SWR*SWR+1))
40 IF Z >R THEN X=SQR(Z*Z -R*R) ELSE X=-SQR(R*R -Z*Z)
50 PRINT "Z=";Z
60 PRINT "SWR=";SWR
70 PRINT "R=";R
80 PRINT "X=";X
90 INPUT X$
100 GOTO 5


73 de Brian/K3KO

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