amdx wrote:
The meter quality has to be higher than the Q of the device being
measured, of a compensation has to be made for the meter losses. For
instance, with the signal generator voltmeter method, I have
calculated the losses in the two 10X probes, to prove to myself that
the errors they cause are not significant up to the highest Q values I
measured, this way. I would have had to measure a Q near 1000 before
they would have altered a significant digit of the measurement. But I
did convince myself that energy absorption outside the coil in
surrounding objects is significant, since shifting my position in my
chair did change the measurement.


It has been a while since I measured the 3db points of a inductor, but I
think the probe did load the coil. I recall putting a 1meg resistor in
series
with the probe to help isolate the probe capacitance from the inductor.

Any Q measurement of a tuned circuit must pull less energy from the
tank than the tank consumes each cycle, if the meter's effect can be
neglected. The Boonton 160A injects a voltage into the tank with a
fraction of an ohm source impedance. And a vacuum tube volt meter
measures the resultant voltage across the tank. Both these paths
represent a loss, and limit the highest possible Q reading to about
400. But some tank impedance combinations (very high impedance
affected by volt meter input impedance, or very low impedance affected
by voltage source impedance) may face more severe limits.

I bridge type measurement can be zeroed for its internal losses before
the measurement, so is more self compensating. But any equipment I
have seen will have trouble accurately measuring extremely high Q
tanks, inductors or capacitors.