[TowerTalk] S21 to Rp & Cp - Equivalent Circuit

[jimlux]

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)