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## [TowerTalk] 160m shunt feed followup

 To: [TowerTalk] 160m shunt feed followup alsopb@gloryroad.net (alsopb) Mon, 01 Oct 2001 16:51:24 +0000
 ``` 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 List Sponsored by AN Wireless: AN Wireless handles Rohn tower systems, Trylon Titan towers, coax, hardline and more. Also check out our self supporting towers up to 100 feet for under \$1500!! http://www.anwireless.com ----- FAQ on WWW: http://www.contesting.com/FAQ/towertalk Submissions: towertalk@contesting.com Administrative requests: towertalk-REQUEST@contesting.com Problems: owner-towertalk@contesting.com ```
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