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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: Fri, 12 Jan 2018 08:16:58 -0800
List-post: <mailto:towertalk@contesting.com>
On 1/12/18 7:57 AM, Steve Hunt wrote:
Yes!!!! - S11 Magnitude and Phase are quite different from S21 Magnitude and Phase.
If you are interested, here's how I derive the choke's complex impedance 
from S21 Magnitude and Phase:
http://www.karinya.net/g3txq/chokes/s21.pdf


The conversion of Mag/Phase to complex values is the same, but the conversion of the measurement to Z is different...
in the 1 port measurement, the unknown is in series with the 50 ohm 
impedance of the source, so you're looking at the ratio of the 
voltage/current across the Z compared to the voltage/current across the 
series combination (with some math to turn it into gamma/S11)
In the 2 port measurement, the unknown is between the ports, so you're 
looking at the voltage/current across the port 2 load, compared with the 
voltage/current at the port 1 source (with some math to turn it into S21)
Steve's website has the equations.

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