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