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).
--
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

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).
--
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

On Sat, 17 Apr 2004 15:46:59 GMT, James Meyer
wrote:

On Sat, 17 Apr 2004 07:43:49 GMT, Robert Baer posted
this:

John Larkin wrote:


Well, all the usual methods: resonance width, phase shift, ringdown,
stuff like that. I work with gadgets with Qs over 1e9, and people
measure them without difficulty.

John

Ringdown is the easist way when Qs are extremely high.

You must still account for the energy you extract from the circuit in
order to measure the ringdown. Even the energy needed to drive a high impedance
probe is significant when the Q gets high.

IOW, the Q without the probe will be higher than the Q when you insert
the probe to measure the Q.

Jim


Of course, you can account for the probe loss when you do the math. Or
leave the probe disconnected during a ringdown, and add it after some
delay to see how much energy is left in the system.

John

On Sat, 17 Apr 2004 15:46:59 GMT, James Meyer
wrote:

On Sat, 17 Apr 2004 07:43:49 GMT, Robert Baer posted
this:

John Larkin wrote:


Well, all the usual methods: resonance width, phase shift, ringdown,
stuff like that. I work with gadgets with Qs over 1e9, and people
measure them without difficulty.

John

Ringdown is the easist way when Qs are extremely high.

You must still account for the energy you extract from the circuit in
order to measure the ringdown. Even the energy needed to drive a high impedance
probe is significant when the Q gets high.

IOW, the Q without the probe will be higher than the Q when you insert
the probe to measure the Q.

Jim


Of course, you can account for the probe loss when you do the math. Or
leave the probe disconnected during a ringdown, and add it after some
delay to see how much energy is left in the system.

John

Robert Baer wrote in message ...
....
Yes, but the emphasis was on small size, and a helical resonator
allows a goodly shrinkage of volume wihout a corresponding loss large of
Q.

As compared with what? A given coil in a helical resonator will
result in lower Qu than that same coil unshielded and simply resonated
with a good capacitor.


....
Maybe his requirements are not too realistic?

Seems to commonly be the case.

Robert Baer wrote in message ...
....
Yes, but the emphasis was on small size, and a helical resonator
allows a goodly shrinkage of volume wihout a corresponding loss large of
Q.

As compared with what? A given coil in a helical resonator will
result in lower Qu than that same coil unshielded and simply resonated
with a good capacitor.


....
Maybe his requirements are not too realistic?

Seems to commonly be the case.

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.

Jim

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.

Jim

On Sat, 17 Apr 2004 10:04:36 -0700, John Larkin
posted this:

On Sat, 17 Apr 2004 15:46:59 GMT, James Meyer
wrote:

IOW, the Q without the probe will be higher than the Q when you insert
the probe to measure the Q.

Jim


Of course, you can account for the probe loss when you do the math. Or
leave the probe disconnected during a ringdown, and add it after some
delay to see how much energy is left in the system.

John

If you have to "do the math", you might as well just calculate the Q
from first principles and forget the "measurement".

Jim

On Sat, 17 Apr 2004 10:04:36 -0700, John Larkin
posted this:

On Sat, 17 Apr 2004 15:46:59 GMT, James Meyer
wrote:

IOW, the Q without the probe will be higher than the Q when you insert
the probe to measure the Q.

Jim


Of course, you can account for the probe loss when you do the math. Or
leave the probe disconnected during a ringdown, and add it after some
delay to see how much energy is left in the system.

John

If you have to "do the math", you might as well just calculate the Q
from first principles and forget the "measurement".

Jim