James Meyer wrote in message . ..
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.

ONLY if it's really big. See Reg's posting in this thread on that
subject. We're talking about making things small here, like smaller
than a 1 inch diameter coil at 18MHz. The cavity for a standard
helical resonator design will ding the Q by 15% or more; for such a
small unshielded coil do you expect that much radiation? I don't.
Not even close.

Cheers,
Tom

James Meyer wrote in message . ..
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.

ONLY if it's really big. See Reg's posting in this thread on that
subject. We're talking about making things small here, like smaller
than a 1 inch diameter coil at 18MHz. The cavity for a standard
helical resonator design will ding the Q by 15% or more; for such a
small unshielded coil do you expect that much radiation? I don't.
Not even close.

Cheers,
Tom

On Sat, 17 Apr 2004 18:56:14 -0700, Roy Lewallen posted this:


Thanks for the profound observation about mathematicians and engineers.
In which category does one put a person who's satisfied with
calculations made without thinking about, caring about, or considering
the errors caused by ignoring fundamental effects? Certainly not an
engineer as I use the term.

Roy Lewallen, W7EL

Such a person as you describe is commonly known as a physicist. I have
had to work with several. That some of them are still alive is a testament to
my degree of self control.

Jim

On Sat, 17 Apr 2004 18:56:14 -0700, Roy Lewallen posted this:


Thanks for the profound observation about mathematicians and engineers.
In which category does one put a person who's satisfied with
calculations made without thinking about, caring about, or considering
the errors caused by ignoring fundamental effects? Certainly not an
engineer as I use the term.

Roy Lewallen, W7EL

Such a person as you describe is commonly known as a physicist. I have
had to work with several. That some of them are still alive is a testament to
my degree of self control.

Jim

I read in sci.electronics.design that James Meyer
wrote (in ) about 'A neat
and compact way to generate RF harmonics...', on Sun, 18 Apr 2004:
On Sat, 17 Apr 2004 18:56:14 -0700, Roy Lewallen posted this:


Thanks for the profound observation about mathematicians and engineers.
In which category does one put a person who's satisfied with
calculations made without thinking about, caring about, or considering
the errors caused by ignoring fundamental effects? Certainly not an
engineer as I use the term.

Roy Lewallen, W7EL

Such a person as you describe is commonly known as a physicist. I have
had to work with several. That some of them are still alive is a testament to
my degree of self control.

LOL! But physicists are usually *preoccupied* with fundamental effects
and tend to ignore others.

In my brief skirmish with aeronautical engineering, I formed the opinion
that most of the calculations were as pragmatic as RL suggests; the only
consolation is that they seem to work.
--
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 Sun, 18 Apr 2004:
On Sat, 17 Apr 2004 18:56:14 -0700, Roy Lewallen posted this:


Thanks for the profound observation about mathematicians and engineers.
In which category does one put a person who's satisfied with
calculations made without thinking about, caring about, or considering
the errors caused by ignoring fundamental effects? Certainly not an
engineer as I use the term.

Roy Lewallen, W7EL

Such a person as you describe is commonly known as a physicist. I have
had to work with several. That some of them are still alive is a testament to
my degree of self control.

LOL! But physicists are usually *preoccupied* with fundamental effects
and tend to ignore others.

In my brief skirmish with aeronautical engineering, I formed the opinion
that most of the calculations were as pragmatic as RL suggests; the only
consolation is that they seem to work.
--
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 23:48:01 GMT, James Meyer
wrote:

On Sat, 17 Apr 2004 12:22:03 -0700, Roy Lewallen posted this:

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 was responding to a suggestion that one could do the math to calculate
what the Q would have been if you hadn't tried to measure it. I was pointing
out that if you could do that math, and get it correct, that you could do the
whole exercise with math and forget measuring anything.


The math in question is trivial. Qs from 1 to 1e9 can be measured
accurately without difficulty.


An engineer knows when to say "close enough". A mathematician is never
satisfied.

But then, mathematicians don't measure things, do they?

John

On Sat, 17 Apr 2004 23:48:01 GMT, James Meyer
wrote:

On Sat, 17 Apr 2004 12:22:03 -0700, Roy Lewallen posted this:

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 was responding to a suggestion that one could do the math to calculate
what the Q would have been if you hadn't tried to measure it. I was pointing
out that if you could do that math, and get it correct, that you could do the
whole exercise with math and forget measuring anything.


The math in question is trivial. Qs from 1 to 1e9 can be measured
accurately without difficulty.


An engineer knows when to say "close enough". A mathematician is never
satisfied.

But then, mathematicians don't measure things, do they?

John

John,
Are you saying you have some SRDs available?
I could use a couple in a GPR I'm working on.
Part of the Sample pulse generator.
Don

John Larkin wrote:

On Mon, 12 Apr 2004 19:09:51 GMT, "Harold E. Johnson"
wrote:


If you do use diodes for higher-order harmonic generation, and not
just a simple full-wave-rectifier type frequency doubler, I suppose
you want something of the nature of a step recovery diode. That
implies minority carrier stored charge in the diode, and that would
preclude using a Schottky diode (which would work great in the
full-wave-rectifier type doubler). If you get into actually wanting
to generate harmonic combs out to microwave frequencies, it's probably
worthwhile looking for diodes actually characterized for step recovery
service. But I really think that's way beyond what you are trying to
accomplish right now.

My turn to learn something here. Tom, would you elaborate a bit on the above
please? I know SRD's are comb generators out to visible light, but they're
also 50 percent hard to find and 50 percent magic. I've been using
Schottky's for X16 multipliers to 2 GHz, am I doing something wrong? (I keep
promising myself that I'm gonna substitute an MMIC for that one day, I DID
find the "Filter Gain" in the line length from generator to filter), THAT
was both impressive AND helpful. If I go with the MMIC, any preference of
Silicon over GaAs?

Regards

W4ZCB



The only distributor-stock SRDs I know of are the M/Acom MA44767,
MA44768, MA44769 parts, all SOT-23 and dirt cheap. I think Penstock
carries them. The '68 or '69 should be good for multiplication to 2
GHz. For high ratios, an SRD will beat a plain diode by a huge amount.
There are lots of appnotes around about using them as multipliers.

I have a bunch in stock and can send a few to anybody who wants to
play.

John




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