[TowerTalk] One off balun question

[Steve Hunt]

A number of folk have expressed interest via PMs in the spreadsheet I 
use to perform the calculation of choke R and X from the VNA data. In 
case there is wider interest it's available here:
http://www.karinya.net/g3txq/temp/s21/s21_choke_charts.ods

It's a Libre Office Calc file; if anyone has trouble reading it I can 
export an Excel version, but some of the chart formatting may be lost.

The derivation of the calculation of choke R from S21 magnitude and 
phase is shown here:
http://www.karinya.net/g3txq/temp/s21/choke_calc.png

The calculation of choke X easily follows from the value of R, because 
X/(R+75)=tan(theta)

Please note that the VNA calibration is performed with a direct 
connection between Port A and Port B - it does _not_ involve the 50 Ohm 
terminating resistor on the jig; the effect of that resistor is taken 
into account in the subsequent calculations. The two coax leads 
connecting the VNA to the jig _should_, of course be used for the 
calibration run to eliminate any amplitude or phase errors they might 
otherwise introduce.

Finally, here's a tidied up sketch of the set-up:
http://www.karinya.net/g3txq/temp/s21/vna_jig.png

Steve G3TXQ