If you don't ask, you won't find out they say. So here goes, could
capacitor Q be measured using the S21 method?
Richard, K8CYK
On Sun, Mar 21, 2021, 5:56 PM jmr via groups.io <jmrhzu=
[email protected]> wrote:
I tried to repeat Roger's test of a 'Hi Q' 470pF cap with my nanoVNA and
managed to see an indicated Q that was very noisy (as expected) below
10MHz. At 10MHz it was probably averaging a indicated Q of 2000 with the
nanovna. By 20MHz the indicated Q dipped below 800 and the trace was still
very noisy but it was easier to spot the average.
Manfred's plots of the 2000pF 'Hi Q' capacitor (on the EFHW transformer
thread) obviously had a problem somewhere with the test setup or maybe his
2000pF capacitor was faulty? I'd expect the nanoVNA to perform better than
that across the HF bands if given a fighting chance with a decent 2000pF
test capacitor. Obviously, the nanoVNA can't measure the Q of the 2000pF
cap down at lower frequencies but it should perform reasonably well across
the HF bands for example.
In Roger's case, a decent 470pF cap is probably best tested across 5MHz to
20MHz. Below this the nanoVNA will increasingly limit the measurement and
it becomes meaningless to even try measuring the Q of the cap much below
5MHz unless it is not a high Q cap.
