On Mon, 10 Dec 2007 21:04:06 GMT, Owen Duffy wrote:

I can't quickly think of a sampling technique that truly takes a
point sample.

Slotted line.

73's
Richard Clark, KB7QHC

Richard Clark wrote in
:

On Mon, 10 Dec 2007 21:04:06 GMT, Owen Duffy wrote:

I can't quickly think of a sampling technique that truly takes a
point sample.

Slotted line.

73's
Richard Clark, KB7QHC


Thanks Richard and Jim,

I mean't literally a point sample, and I doubt that we can manufacture a
probe for either voltage or current that has zero dimensions (ie is
influenced ONLY by conditions at a point of no physical size.).

I go on to say (if you read on) in different words that notwithstanding
that, practical probes can be made that give acceptable accuracy.

They unsaid key thing is that these probes do not depend on averaging
over a length of line (as Roger suggested), that is actually a defect
that limits their usable upper frequency.

Owen

On Tue, 11 Dec 2007 00:36:02 GMT, Owen Duffy wrote:

I mean't literally a point sample, and I doubt that we can manufacture a
probe for either voltage or current that has zero dimensions (ie is
influenced ONLY by conditions at a point of no physical size.).

Hi Owen,

I would say that is arguable given my exposure to research in
Nanotechnology. I've seen one molecule probes (illustrated actually,
by microscopes that do enjoy vastly higher resolutions than were state
of the art 10 years ago; and they can image complex atoms and small
molecules).

These scales are commonly referred to as 1D, or quantum dots. Now,
given a measurement must be made, it demands a probe. Further, given
a quantum dot sized probe, it necessarily describes the smallest size
for which any smaller size yields no more information.

The practicality of it is that this quantum dot would have to reside
at the end of a very thin lead. A carbon nanotube so qualifies, and
they can be grown to considerable length (for this field), and they
themselves occupy no more than 1nM diameter (for a single walled
construction which is not terribly difficult to obtain).

In the practical field of RF, I seriously doubt such a probe/lead
combination would perturb a slotted line. In fact, their influence
would be lost in the decimals far to the right of the accuracy of the
line's construction. Or, I could easily imagine that most computers
would suffer rounding errors long before the probe/lead's influence
could be calculated if the line were perfect.

Yes, for the absolutist (no speaking of you Owen), a probe could never
be small enough, but if it were smaller it would be impossible to
obtain a reading. Sort of self-extermination of the absolutist
argument.

73's
Richard Clark, KB7QHC

Richard Clark wrote:

...
73's
Richard Clark, KB7QHC

Richard:

In my course of study, I was forced to take a class in human
psychology--I hated it--its' use I could not fathom, to one engaged in
the technical aspects of "the real world" it seemed a waste.

However, that class was all about running into the likes of you.

You are an actor on a stage, yet we all wish to view NO performance.
You are a writer, in your imagination--yet we have no interest in your
book. You are all important--to yourself, but you have NO importance to me.

You are a spoiled child who will even accept "negative attention" as
opposed to "no attention at all"--and in all actuality--that is what you
truly deserve.

You are a mess man, get a hold of yourself ... anyone who would even
lend a hand in your support is an idiot--OWN IT MAN! Only an idiot can
befriend you at the present time--grow up ...

Now,
3's :-)

JS

John Smith wrote:
Richard Clark wrote:

...
73's
Richard Clark, KB7QHC

Richard:

In my course of study, I was forced to take a class in human
psychology--I hated it--its' use I could not fathom, to one engaged in
the technical aspects of "the real world" it seemed a waste.

However, that class was all about running into the likes of you.

Don't sweat it, "John". As you've stated, you couldn't fathom "its' use."

You are an actor on a stage, yet we all wish to view NO performance.

Who's "we", "John"? For whom do you speak?

You
are a writer, in your imagination--yet we have no interest in your
book.

Who is "we"? I find Richard's posts quite entertaining.

You are all important--to yourself, but you have NO importance to
me.

Get over it, "John". It isn't all about you, whoever you are.

Dave K8MN

Dave Heil wrote:

Heil, you are an idiot. You are, perhaps the biggest idiot I have run
into in the news groups, and that is saying something, Richard is
second--only to you ... ROFOL

Keep on truckin', if persistence counts, you have one thing going for
you. :-)

JS

John Smith wrote:
Dave Heil wrote:

Heil, you are an idiot. You are, perhaps the biggest idiot I have run
into in the news groups, and that is saying something...

But we are left wondering what it is that is being said. After all,
you're an anonymous CBer who chastises others from the shadows. You
haven't the courage of your convictions, "John".

...Richard is
second--only to you ... ROFOL

Richard is quite obviously an intelligent person. That alone seems
enough to chafe you.

Keep on truckin', if persistence counts, you have one thing going for
you. :-)

Oh, I'm persistent. I can punctuate and spell. I'm interested in
antennas and find your stuff distracting. I find it amusing that
someone of your ilk attacks Richard. I've learned much from reading his
posts and those of W7EL. W8JI's material was most helpful in installing
a beverage antenna. On the other hand, I've never learned anything
useful from you.

Dave K8MN

Richard Clark wrote:
On Mon, 10 Dec 2007 21:04:06 GMT, Owen Duffy wrote:


I can't quickly think of a sampling technique that truly takes a
point sample.


Slotted line.

Doesn't take current sample

Probe is of finite size (albeit small fraction of lambda in most cases)

The difficulty of making accurate RF current measurements at a point is
why things like slotted lines were invented. You can measure voltage at
a series of points and calculate what the current *must* be.

On Mon, 10 Dec 2007 16:16:15 -0800, Jim Lux
wrote:

Richard Clark wrote:
On Mon, 10 Dec 2007 21:04:06 GMT, Owen Duffy wrote:


I can't quickly think of a sampling technique that truly takes a
point sample.


Slotted line.

Doesn't take current sample

Hi Jim,

Never needed to with a slotted line.

Probe is of finite size (albeit small fraction of lambda in most cases)

And the time to measure anything is finite too.

The difficulty of making accurate RF current measurements at a point is
why things like slotted lines were invented. You can measure voltage at
a series of points and calculate what the current *must* be.

At worst, only three points, and generally for SWRs folks here would
agree were astronomical (and incalculable, but I could measure them
anyway).

With four fixed points (nominally eighth wave, but a range of
frequencies can be accommodated), I could determine the complex
impedance of any load. [re. "Microwave Measurements," Ginzton, Sec.
5.12] There are a myriad of other slotted line techniques, but I will
leave them for a suitable occasion.

I have never had to consider what the current *must* be - an
unnecessary elaboration.

73's
Richard Clark, KB7QHC