The rectangular plot of the one port S data is insufficient to
determine Q. You will need the differential phase shift
of the reflection coefficient as well. Taken together with
the appropriate formula the Q can be determined. The chart
facilitates this and overlays that could be clipped onto
the network analyzer screen were available. Or the glass
was etched on screen. Doing this with the nanovna simply
requires the touchstone file and then import this into
the chart program I displayed. There are a other measurement
types available, S21, for example, where the Q is extracted
directly from the screen. Typically, this is a rectangular plot,
although a chart plot can also be used.
The Q is obtained from the reflection coefficient crossing at
zero degrees, 7.003 MHz divided by the 3 dB down power points
where the sweep crosses the Q=1 contour at 7.022 and 6.974 MHz.
The result is 146.
The common name is "constant Q contour" and the Q=1 is somewhat unique in that
it is a locus of points connecting all cases where R=X.
Other contours are available. The Q=2, 3, etc.... where the R,X ratio is 2,3, etc... and this facilitates
the constructs for matching over a desired band when a load model is imported to the chart.
