On 17 Apr 2004 10:09:22 -0700, (Tom Bruhns) posted this:

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.


Not so. And others have pointed that out. If you take an unshielded
coil to it's ultimate configuration you are confronted with a resonant antenna
that is loaded by its radiation resistance and that results in a *lower* Q than
a properly shielded resonator.

Jim

On 17 Apr 2004 10:09:22 -0700, (Tom Bruhns) posted this:

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.


Not so. And others have pointed that out. If you take an unshielded
coil to it's ultimate configuration you are confronted with a resonant antenna
that is loaded by its radiation resistance and that results in a *lower* Q than
a properly shielded resonator.

Jim

On Sat, 17 Apr 2004 19:07:12 GMT, James Meyer
wrote:

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


How can you calculate Q from first principles? 3D EM simulation?
Quantum mechanics?

John

On Sat, 17 Apr 2004 19:07:12 GMT, James Meyer
wrote:

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


How can you calculate Q from first principles? 3D EM simulation?
Quantum mechanics?

John

Ah, just the person I've been waiting for. How do you account for
current bunching on the conductors (that is, non-uniform distribution of
current around the conductors)? What reference, equation, or program do
you use? Nearly all "first principle" calculations of Q I've seen
grossly overestimate Q, and I believe the failure to take this into
account is at least part of the reason. I haven't seen a decent
analytical method of dealing with it, and an anxious to see how you do it.

Then there's surface corrosion and roughness, radiation, and coupling to
nearby objects. How do you deal with those? Have you identified some of
the other factors that often make a simplistic "first principle"
calculation disagree so badly with carefully made measurements?

Roy Lewallen, W7EL

James Meyer wrote:

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

Jim

Ah, just the person I've been waiting for. How do you account for
current bunching on the conductors (that is, non-uniform distribution of
current around the conductors)? What reference, equation, or program do
you use? Nearly all "first principle" calculations of Q I've seen
grossly overestimate Q, and I believe the failure to take this into
account is at least part of the reason. I haven't seen a decent
analytical method of dealing with it, and an anxious to see how you do it.

Then there's surface corrosion and roughness, radiation, and coupling to
nearby objects. How do you deal with those? Have you identified some of
the other factors that often make a simplistic "first principle"
calculation disagree so badly with carefully made measurements?

Roy Lewallen, W7EL

James Meyer wrote:

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

Jim

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.
--
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:
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.
--
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 17:26:15 +0100, John Woodgate
wrote:

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).

I can recall using one of those, some little time back. Anybody have
the schematic diagram for it?

Barry Lennox

On Sat, 17 Apr 2004 17:26:15 +0100, John Woodgate
wrote:

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).

I can recall using one of those, some little time back. Anybody have
the schematic diagram for it?

Barry Lennox