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Have a look at the manual of the Rhode & Schwartz? QMeter

On Thursday, August 4, 2022 at 11:55:19 AM GMT+2, Dr. David Kirkby, Kirkby Microwave Ltd <drkirkby@...> wrote:

On Thu, Aug 4, 2022 at 02:14 AM, Kenneth Greenough wrote:

Re' a Q meter.
This is only a thought idea, not tested hi.
Have a small enclosure with sockets on opposite sides. each socket has a
single turn loop attached with sufficient distance between the two loops
to allow the coil under test to be positioned between them. one turn is fed
from your sig' gen' and the other feeds a scope or RF meter.? A sufficient
level from the sig gen may require an amplifier. With the coil to be tested
placed between the loops tune the sig gen for maximum throughput, ie
resonance. Then tune the sig gen lower until the throughput is 3dB
down, ie 0.71 reduction in voltage or 1/2 power. Repeat by tuning the sig gen
higher than resonance for a similar drop in throughput. the resonant
frequency divided by the bandwidth just ascertained is the Q of the coil.
The coil being tested can, of course, have a capacitor in parallel if wished.
73 Ken G8BEQ

I have seen something like that before. One problem is that it would not work with coils in screened enclosures, some of which are.?I have ordered a couple of Boonton Q-standards, which I was hoping to measure. Those are in screen enclosures, with 2 banana plugs 25.4 mm (1”) apart.?See attached photograph.?

I think capacitive coupling is also possible If the capacitors are very small, the reactance is high, so they present little loading to the coil/capacitor combination.

One really does need a capacitor in parallel with the coil so that one can make the measurement at the frequency of interest, rather than the self resonant frequency of the inductor.?

Dave