I read in sci.electronics.design that James Meyer
wrote (in ) about 'A neat
and compact way to generate RF harmonics...', on Sat, 17 Apr 2004:
On Sat, 17 Apr 2004 21:05:34 +0100, John Woodgate
posted this:

I read in sci.electronics.design that James Meyer
wrote (in ) about 'A neat
and compact way to generate RF harmonics...', on Sat, 17 Apr 2004:
On Sat, 17 Apr 2004 17:26:15 +0100, John Woodgate
posted this:

I read in sci.electronics.design that James Meyer
wrote (in ) about 'A neat
and compact way to generate RF harmonics...', on Sat, 17 Apr 2004:
IOW, the Q without the probe will be higher than the Q when you
insert
the probe to measure the Q.

Use an inductive current pick-off. That how the Marconi Instruments 1245
series Q-meters work(ed).

Nevertheless, *ANY* method used to probe the field associated with the
resonator will load the resonator and degrade the Q.

IIRC, the Marconi unit used a 10 nH inductor (maybe less) made of a
short length of silver wire, gold-plated to eliminate sulfide attack.
The effect on Q would be minimal in the extreme.

But what about the energy extracted from the probe to make the
measurement?

The sensing inductor was connected to the grid of a triode tube, with,
IIRC, a 1 Mohm grid leak. With 1 mV across the sensor, that's a whole
1 uJ/s of energy extraction.

Any load on the probe is transformed into a load on the resonator.
Compensating for that load requires a very small number be divided by another
very small number. Any error in either number makes a much larger error in the
result of the calculation.

Check your math. It's small errors in *differences*, not in ratios, that
result in large errors in results.
--
Regards, John Woodgate, OOO - Own Opinions Only.
The good news is that nothing is compulsory.
The bad news is that everything is prohibited.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk