On Thu, Aug 24, 2023 at 12:46 PM, Andrew (G1RVD G0Z) wrote:
Let's say one measures the impedance of an antenna, reading the S11 parameters
from the NanoVNA via USB, converting the reflection coefficients to real &
imaginary impedances (thank you Rich NE1EE for your spreadsheet). Does
anyone have a spreadsheet to calculate the necessary reactance (L C) that
needs to be added in a L match tuner (with series L)? Effectively, a
spreadsheet, or formula, that replicates what one would normally use a Smith
chart to achieve.
A couple of things to consider:
- When you say "measure the impedance of the antenna" in this case you are really measuring the impedance at the end of the coax feedline. It will be much different at the antenna feedpoint.
- Make sure that you don't have any current flowing on the outer surface of the shield (the "3rd wire"). This usually requires a balun or RF choke ("isolator"). If you don't do this the measured impedance will change when you connect the USB cable which has a ground shield on it. You can check by measuring the impedance on the NanoVNA with and without the USB cable attached.
- There is a LC match feature in recent DiSlord firmware for the NanoVNA
- If you have a copy of the ARRL Antenna Book the CD comes with a program called TLW that will design various type of tuners and gives their matching efficiency.
- Here is an online LC match calculator:
Roger
Roger Need