On Mon, Nov 22, 2021 at 11:53 AM, Joe WB9SBD wrote:
I'm trying to understand a few things in your pictures, the one where you are
at max "C" makes sense to me, the other looks more like a dead short, the
curve for the smith is either not there or very very short.
The NanoVNA measures the complex impedance R + jX. For a air variable R is very small and for a very small capacitance like 8 pF the reactance X is very high under 10 MHz. At 10 MHz. it is 1/(2*pi*8e-12*10e6) = 1,990 ohms and 19,900 ohms at 1 MHz. . So on the Smith chart when you plot from 1 to 10 MHz. it is just a fat dot at the right hand side.
and what is circles in the red box about?
The Smith Chart marker can be set to show the "effective capacitance". I put a red box around it to show the value of 8.3 pF with the capacitor open at 9.34 MHz. (same as NanoVNA app graph) and with the cap closed at 8.83 MHz. yielding 365 pF. The other red boxes are just the magnitude of the complex impedance |Z| which I was measuring for an experiment I was doing and can be ignored.
Roger
Roger Need