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

[jimlux <jimlux@earthlink.net>]

On 1/12/18 7:50 AM, Máximo EA1DDO_HK1H wrote:
> Is a different formula to convert LogMag(dB) & Phase from S11 than from S21?
No, it's the same. But calculating Z from S11 (a one port measurement) 
is different than calculating it from S21 (a two port measurement) - if 
you've got the Z in series between the ports it's different than if you 
have something like the Z and a resistor in series, or something like that.


> ________________________________
> De: TowerTalk <towertalk-bounces@contesting.com> en nombre de Steve Hunt 
> <steve@karinya.net>
> Enviado: viernes, 12 de enero de 2018 13:47
> Para: towertalk@contesting.com
> Asunto: Re: [TowerTalk] S21 to Rp & Cp - Equivalent Circuit
>
> I thought Maximo was trying to derive R and X from S21 measurements, not
> S11 measurements - at least that's what his Subject line suggests.
>
> Steve G3TXQ
>
>
> > working in Octave (free version of Matlab), which is a bit easier than
> > Excel
> >
> > > > s11mag = -29.6
> > s11mag = -29.600
> > > > s11ph = -77.1
> > s11ph = -77.100
> > > > gamma = 10^(s11mag/20)
> > gamma =  0.033113
> > > > gamma = gamma*complex(cos(s11ph/180*pi),sin(s11ph/180*pi))
> > gamma =  0.0073925 - 0.0322774i
> > > > z = 50* ( 1+gamma)/(1-gamma)
> > z =  50.6383 -  3.2725i
> >
> > This is the series form, and close to 50 ohms, as expected (a return
> > loss of 30dB is a good match)
> > Convert to parallel form
> >
> > > > rs = real(z)
> > rs =  50.638
> > > > xs = imag(z)
> > xs = -3.2725
> > > > comterm = (rs/xs+xs/rs)
> > comterm = -15.538
> > > > rp=xs*comterm
> > rp =  50.850
> > > > xp = rs*comterm
> > xp = -786.84
> > > >
> > Which matches *neither* of the other versions.
> >
> > And using a different way to convert series to parallel
> > > > Q = xs/rs
> > Q = -0.064626
> >
> > > > xp = xs*(Q^2+1)/Q^2
> > xp = -786.84
> > > > rp=rs/(Q^2+1)
> > rp =  50.428
> > > >
> > Slightly different R - maybe it's a numerical precision thing Q^2 is
> > small
> >
> >
> > _______________________________________________
> >
> >
> >
> > _______________________________________________
> > TowerTalk mailing list
> > TowerTalk@contesting.com
> > http://lists.contesting.com/mailman/listinfo/towertalk
> TowerTalk Info Page - 
> Contesting<http://lists.contesting.com/mailman/listinfo/towertalk>
> lists.contesting.com
> TowerTalk is for discussion of tower and HF antenna construction topics. TT 
> members have lots of helpful information and are happy to share it.
>
>
>
> _______________________________________________
>
>
>
> _______________________________________________
> TowerTalk mailing list
> TowerTalk@contesting.com
> http://lists.contesting.com/mailman/listinfo/towertalk
> TowerTalk Info Page - 
> Contesting<http://lists.contesting.com/mailman/listinfo/towertalk>
> lists.contesting.com
> TowerTalk is for discussion of tower and HF antenna construction topics. TT 
> members have lots of helpful information and are happy to share it.
>
>
> _______________________________________________
>
>
>
> _______________________________________________
> TowerTalk mailing list
> TowerTalk@contesting.com
> http://lists.contesting.com/mailman/listinfo/towertalk
_______________________________________________



_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk