To: | towertalk@contesting.com |
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Subject: | Re: [TowerTalk] S21 to Rp & Cp - Equivalent Circuit |
From: | jimlux <jimlux@earthlink.net> |
Date: | Fri, 12 Jan 2018 06:24:43 -0800 |
List-post: | <mailto:towertalk@contesting.com> |
On 1/12/18 5:47 AM, Steve Hunt wrote: 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 I'd have to go back and look - maybe that's the hiccup I'm still curious about the Excel/Octave variance though. 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 - 3.2725iThis 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 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 |
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