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Re: [TowerTalk] S21 to Rp & Cp - Equivalent Circuit

To: towertalk@contesting.com
Subject: Re: [TowerTalk] S21 to Rp & Cp - Equivalent Circuit
From: jimlux <jimlux@earthlink.net>
Date: Thu, 11 Jan 2018 10:48:05 -0800
List-post: <mailto:towertalk@contesting.com>
On 1/11/18 10:01 AM, Máximo EA1DDO_HK1H wrote:
Hi Jim, Steve, all,


Playing with those formulas I´ve got an inconsistency.


To get R and jX from LogMag and Phase I can use two different formulas, one from 
Steve and one from Jim, but the results are not same, so I don´t know where the 
mistake is.


Example from Excel;


LogMag -29.601925

Phase  -77.10851


Steve´s formula:

Rx = (100*10^(-LogMag/20))/(SQRT(1+(TAN(Phase/57.29578))^2))-100  =  573.916

X = -(Rx+100)*TAN(Phase/57.29578)  =  2944.484



Jim´s formula:


R = 
COMPLEX(10^((LogMag/20)*(COS((Phase*PI())/180))),10^((LogMag/20)*(SIN((Phase*PI())/180))))

then Rx+jX = IMPRODUCT(50,IMDIV(IMSUM(1,R),IMSUB(1,R)))  =  -49.930  +3.606


As you can see, 573 is not same as -49 OHm

And 2944 is not 3.606


Anyone know where the error is?


Thank you





I'll take a look later this afternoon..
It should just be algebra.

There's clearly an error in mine (negative resistance)

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