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Old March 14th 08, 06:57 PM posted to rec.radio.amateur.antenna
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Default Antenna physical size

Richard Harrison wrote:

Build a small scale model that can be tested indoors and report its
characteristics. Antennas are scaleable.


That's more easily said than done. One of the critical characteristics
of a small antenna is loss. And to correctly replicate loss in a scaled
antenna requires scaling the conductivity of the conductors as the
square root of the frequency. To scale to a higher frequency requires
that the conductivity be better than the original. Unless the original
is made from lead and the scale factor moderate, this wouldn't be possible.

Roy Lewallen, W7EL
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Old March 16th 08, 01:18 AM posted to rec.radio.amateur.antenna
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Default Antenna physical size

On Fri, 14 Mar 2008 11:57:41 -0700, Roy Lewallen wrote:

Richard Harrison wrote:

Build a small scale model that can be tested indoors and report its
characteristics. Antennas are scaleable.


That's more easily said than done. One of the critical characteristics
of a small antenna is loss. And to correctly replicate loss in a scaled
antenna requires scaling the conductivity of the conductors as the
square root of the frequency. To scale to a higher frequency requires
that the conductivity be better than the original. Unless the original
is made from lead and the scale factor moderate, this wouldn't be
possible.


If what I suspect is true, would not the coax also need to be scaled?

- 73 de Mike N3LI -

--
-73 de Mike N3LI -
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Old March 18th 08, 07:53 AM posted to rec.radio.amateur.antenna
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Default Antenna physical size

Mike Coslo wrote:
On Fri, 14 Mar 2008 11:57:41 -0700, Roy Lewallen wrote:

Richard Harrison wrote:
Build a small scale model that can be tested indoors and report its
characteristics. Antennas are scaleable.

That's more easily said than done. One of the critical characteristics
of a small antenna is loss. And to correctly replicate loss in a scaled
antenna requires scaling the conductivity of the conductors as the
square root of the frequency. To scale to a higher frequency requires
that the conductivity be better than the original. Unless the original
is made from lead and the scale factor moderate, this wouldn't be
possible.


If what I suspect is true, would not the coax also need to be scaled?


Dunno. What do you suspect?

Roy Lewallen, W7EL
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Old March 18th 08, 05:26 PM posted to rec.radio.amateur.antenna
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Default Antenna physical size

Roy Lewallen wrote:
Mike Coslo wrote:
On Fri, 14 Mar 2008 11:57:41 -0700, Roy Lewallen wrote:

Richard Harrison wrote:
Build a small scale model that can be tested indoors and report its
characteristics. Antennas are scaleable.
That's more easily said than done. One of the critical characteristics
of a small antenna is loss. And to correctly replicate loss in a scaled
antenna requires scaling the conductivity of the conductors as the
square root of the frequency. To scale to a higher frequency requires
that the conductivity be better than the original. Unless the original
is made from lead and the scale factor moderate, this wouldn't be
possible.


If what I suspect is true, would not the coax also need to be scaled?


Dunno. What do you suspect?


I suspect that the antenna is a tuned circuit on top of coax, and it
needs that coax to radiate effectively. So just scaling the antenna
wouldn't translate to the same results?

- 73 de Mike N3LI -
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Old March 18th 08, 05:41 PM posted to rec.radio.amateur.antenna
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Default Antenna physical size

Michael Coslo wrote:
Roy Lewallen wrote:
Mike Coslo wrote:
On Fri, 14 Mar 2008 11:57:41 -0700, Roy Lewallen wrote:

Richard Harrison wrote:
Build a small scale model that can be tested indoors and report its
characteristics. Antennas are scaleable.
That's more easily said than done. One of the critical characteristics
of a small antenna is loss. And to correctly replicate loss in a scaled
antenna requires scaling the conductivity of the conductors as the
square root of the frequency. To scale to a higher frequency requires
that the conductivity be better than the original. Unless the original
is made from lead and the scale factor moderate, this wouldn't be
possible.

If what I suspect is true, would not the coax also need to be scaled?


Dunno. What do you suspect?


I suspect that the antenna is a tuned circuit on top of coax, and it
needs that coax to radiate effectively. So just scaling the antenna
wouldn't translate to the same results?


Yes. If the coax is radiating, it's part of the antenna. To make an
accurate scale model of the antenna, you have to scale the entire
antenna (that is, every radiating conductor), not just some part of it
which someone has declared to be "The Antenna". In this case, however,
radiating coax isn't likely to be a major fraction of the total loss, so
scaling it in a model probably wouldn't make much difference to the
loss. Its diameter might have a noticeable effect on how much current it
gets and therefore how much it radiates, though, which is an argument in
favor of scaling it.

Roy Lewallen, W7EL


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Old March 18th 08, 05:56 PM posted to rec.radio.amateur.antenna
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Default Antenna physical size

On Mar 18, 12:26 pm, Michael Coslo wrote:
Roy Lewallen wrote:
Mike Coslo wrote:
On Fri, 14 Mar 2008 11:57:41 -0700, Roy Lewallen wrote:


Richard Harrison wrote:
Build a small scale model that can be tested indoors and report its
characteristics. Antennas are scaleable.
That's more easily said than done. One of the critical characteristics
of a small antenna is loss. And to correctly replicate loss in a scaled
antenna requires scaling the conductivity of the conductors as the
square root of the frequency. To scale to a higher frequency requires
that the conductivity be better than the original. Unless the original
is made from lead and the scale factor moderate, this wouldn't be
possible.


If what I suspect is true, would not the coax also need to be scaled?


Dunno. What do you suspect?


I suspect that the antenna is a tuned circuit on top of coax, and it
needs that coax to radiate effectively. So just scaling the antenna
wouldn't translate to the same results?

- 73 de Mike N3LI -


If you are familiar with computor programming then why not model it
instead of repeating over and over again this transmission line
radiation theory.?
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Old March 19th 08, 12:27 PM posted to rec.radio.amateur.antenna
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Default Antenna physical size

Art Unwin wrote:
On Mar 18, 12:26 pm, Michael Coslo wrote:
Roy Lewallen wrote:
Mike Coslo wrote:
On Fri, 14 Mar 2008 11:57:41 -0700, Roy Lewallen wrote:
Richard Harrison wrote:
Build a small scale model that can be tested indoors and report its
characteristics. Antennas are scaleable.
That's more easily said than done. One of the critical characteristics
of a small antenna is loss. And to correctly replicate loss in a scaled
antenna requires scaling the conductivity of the conductors as the
square root of the frequency. To scale to a higher frequency requires
that the conductivity be better than the original. Unless the original
is made from lead and the scale factor moderate, this wouldn't be
possible.
If what I suspect is true, would not the coax also need to be scaled?
Dunno. What do you suspect?

I suspect that the antenna is a tuned circuit on top of coax, and it
needs that coax to radiate effectively. So just scaling the antenna
wouldn't translate to the same results?

- 73 de Mike N3LI -


If you are familiar with computor programming then why not model it
instead of repeating over and over again this transmission line
radiation theory.?



It comes up in the conversation Art, I only rinse and repeat as necessary.

I'm still trying to wrap my mind around the antenna, I'm nowhere near
ready to model it. So as to not make any ignorant mistakes, the antenna
is counter-wound inductors, correct? and they are concurrently wound, as
in they sort of weave against each other? And this is a full wave
antenna? Do you use enameled wire, or what is the insulation? I'm
assuming that this might be important in regards to VF.

- 73 de Mike N3LI -
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Old March 19th 08, 04:58 PM posted to rec.radio.amateur.antenna
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Default Antenna physical size

On Mar 19, 7:27 am, Michael Coslo wrote:
Art Unwin wrote:
On Mar 18, 12:26 pm, Michael Coslo wrote:
Roy Lewallen wrote:
Mike Coslo wrote:
On Fri, 14 Mar 2008 11:57:41 -0700, Roy Lewallen wrote:
Richard Harrison wrote:
Build a small scale model that can be tested indoors and report its
characteristics. Antennas are scaleable.
That's more easily said than done. One of the critical characteristics
of a small antenna is loss. And to correctly replicate loss in a scaled
antenna requires scaling the conductivity of the conductors as the
square root of the frequency. To scale to a higher frequency requires
that the conductivity be better than the original. Unless the original
is made from lead and the scale factor moderate, this wouldn't be
possible.
If what I suspect is true, would not the coax also need to be scaled?
Dunno. What do you suspect?
I suspect that the antenna is a tuned circuit on top of coax, and it
needs that coax to radiate effectively. So just scaling the antenna
wouldn't translate to the same results?


- 73 de Mike N3LI -


If you are familiar with computor programming then why not model it
instead of repeating over and over again this transmission line
radiation theory.?


It comes up in the conversation Art, I only rinse and repeat as necessary.

I'm still trying to wrap my mind around the antenna, I'm nowhere near
ready to model it. So as to not make any ignorant mistakes, the antenna
is counter-wound inductors, correct? and they are concurrently wound, as
in they sort of weave against each other? And this is a full wave
antenna? Do you use enameled wire, or what is the insulation? I'm
assuming that this might be important in regards to VF.

- 73 de Mike N3LI -


I think you should forget the whole idea. We have another expert
on line that can voutch for the fact that it is just a dummy load.
He joins the majority and I am only one,.....who actually has one no
less.!
Art
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Old March 18th 08, 09:15 AM posted to rec.radio.amateur.antenna
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Default Antenna physical size


"Roy Lewallen" wrote in message
...
Richard Harrison wrote:

Build a small scale model that can be tested indoors and report its
characteristics. Antennas are scaleable.


That's more easily said than done. One of the critical characteristics of
a small antenna is loss. And to correctly replicate loss in a scaled
antenna requires scaling the conductivity of the conductors as the square
root of the frequency. To scale to a higher frequency requires that the
conductivity be better than the original. Unless the original is made from
lead and the scale factor moderate, this wouldn't be possible.

Roy Lewallen, W7EL


Hi Roy

I'm curious to know why you didnt use stainless steel as an example rather
than lead as your example.

Jerry


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Old March 18th 08, 05:34 PM posted to rec.radio.amateur.antenna
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Default Antenna physical size

Jerry wrote:
"Roy Lewallen" wrote in message
...
Richard Harrison wrote:
Build a small scale model that can be tested indoors and report its
characteristics. Antennas are scaleable.

That's more easily said than done. One of the critical characteristics of
a small antenna is loss. And to correctly replicate loss in a scaled
antenna requires scaling the conductivity of the conductors as the square
root of the frequency. To scale to a higher frequency requires that the
conductivity be better than the original. Unless the original is made from
lead and the scale factor moderate, this wouldn't be possible.

Roy Lewallen, W7EL


Hi Roy

I'm curious to know why you didnt use stainless steel as an example rather
than lead as your example.


The main reason is that many years ago I was involved in using physical
models scaled up in size in order to optimize microstrip transitions and
other features used for time domain equipment having rise times on the
order of 10 ps. At that time, I looked to see if it was possible to
model the loss accurately, and found I'd need a semiconductor to do it.
I recall that lead was about the least conductive common metal
available. So I tossed that one out in my example.

I don't remember investigating stainless or other steels, but that might
indeed be a way to do it. To make a strictly accurate scale model, the
permeability and permittivity (dielectric constant) stay fixed with
frequency, so a non-magnetic stainless steel would be necessary.
However, since the skin depth is inversely proportional to the square
root of permeability, a magnetic material has the loss of a non-magnetic
material having a conductivity lower by a factor equal to its relative
permeability. So a magnetic material such as steel or magnetic stainless
steel might be used to extend the range of possible loss values
available for making larger physical models. There's a very large number
of steel and stainless steel alloys, and good information on the
required parameters can be hard or impossible to find. So samples would
probably have to be measured.

In the case in question, however, a smaller scale model was proposed,
and we can probably assume that the original is made from copper. So
it's not really possible to create a smaller scale model which
accurately imitates the loss of the original.

Roy Lewallen, W7EL


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