Antenna physical size
 

Ian White GM3SEK wrote in news:U5VH68Pl733HFA
:

Owen Duffy wrote:
Ian White GM3SEK wrote in
:

Alternatively, wind the wire onto a mandrill.

Or would that be a mandrel?


I've seen both spellings recommended in print, but winding wire onto a
mandrill will be far more entertaining.

Ah, when popularity displaces correctness!

But, I can see the confusion when you place a mandrel into a drill to
wind the coil.

Or should it be a persondrel? Is PC still in vogue?

Owen

PS: my (rather old) Concise Oxford Dictionary thinks a mandrill is a
"Large fierce West African baboon", fierce I guess when bound with wire.
It hasn't caught up with the alternative use for mandrel, well not by
1979.

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

Antenna physical size
 

I can bear it no longer. We have Art the English educated antenna expert
who cannot write the English language,and now a Scot who doesn't know that a
Mandrill is a West African Baboon.
If you wind Art's wire on a Baboon it is going to get seriously ****ed off.
From an elderly Pom in Aus.
"Ian White GM3SEK" wrote in message
...
Michael Coslo wrote:
David G. Nagel wrote:
Dave Heil wrote:

Well, there it is. I'm going to scrounge a "former" and a "sowing"
needle and get right to work.

Dave K8MN
Don't forget an 'apon'....


Can you guys tell us the correct way to spell coil former? It's a
bobbin made of insulating material upon which wire is wound.

Alternatively, wind the wire onto a mandrill.


--

73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek

Antenna physical size
 

I can`t find it now, but I believe Mark, NM5K on this thread wrote that
my quotation from page 929 of Terman`s 1955 opus raised flags. I said I
was surprised in my original posting. I was aware at the time that Kraus
shows identical field paterns for a small loop an a short dipole, but
the E and H fields are exchaged between the two antenna types. The Kraus
diagrams are on page 58 of the 3rd edition of "Antennas".

I`ve learned not to quarrel with Terman. So, I reread the page 929
quotation. I posted it correctly. He did say a loop antenna responds
much less to the electric induction field than does a simple wire
antenna of comparable intercept area.

So I looked for a similar statement in Terman`s "Radio Engineering" in
an edition published in 1947. On page 664, I find:
"In the case of a doublet antenna, the electrostatic induction field
becomes proportionally stronger than the magnetic induction field as one
comes closer to the antenna. With the loop antenna the reverse is true."

We know that the induction, or near, field is equal to the radiation
field at about 1/6 wavelength. Closer to the radiator, the induction
field is much stronger. Farther away, the radiation field predominates
Our intrest is usually in the radiation, or far field. Measurements are
usually made several wavelengths away from an antenna to be sure the
induction field has become insignificant.

I`ve thought how and why my experience confirms Terman`s statements
but I won`t bore anyone with these thoughts.

Best regards, Richard Harrison, KB5WZI

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 -

Antenna physical size
 

Dave Heil wrote:
Michael Coslo wrote:
David G. Nagel wrote:
Dave Heil wrote:

Well, there it is. I'm going to scrounge a "former" and a "sowing"
needle and get right to work.

Dave K8MN


Don't forget an 'apon'....


Can you guys tell us the correct way to spell coil former? It's a
bobbin made of insulating material upon which wire is wound. Here's
one that got a patent:

http://www.patentstorm.us/patents/6262650.html

You've done well, Mike. Now what is a "sowing needle" and what might an
"apon" be?

Those are typos. I just figure we should only rib Art on the real
typos. 8^)


Dave K8MN
the product of an inferior American education
(at least according to Art Unwin)

Me too 8^)

- 73 d eMike N3LI -

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

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

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.?

Antenna physical size
 

Ian White GM3SEK wrote:


Alternatively, wind the wire onto a mandrill.


Howl! Almost lost my coffee on that one....

- 73 de Mike N3LI -