OK thanks... Actually I was reading something that indicated you
should add in a velocity factor for the tube when using it as a
sleeve. I had never heard of that either, so I wasn't sure. They used .
95 I believe.

So I guess you would go coax center conductor to tube section #1,
braid to center of second coax through section #1 to section #2. Coax
from section #1 through section #2 to section #3 and so on?

DD

On Tue, 5 Feb 2008 15:06:40 -0800 (PST), Dave99
wrote:

OK thanks... Actually I was reading something that indicated you
should add in a velocity factor for the tube when using it as a
sleeve. I had never heard of that either, so I wasn't sure. They used .
95 I believe.

Hi Dave,

I presume you mean 0.95, which for a metal tube holding an inner
conductor that is air insulated, then that might be operative. Too
much is left unsaid: like frequency/wavelength, size of tube, any
inner conductor (so as to emulate a coax), any coax within the tube
(to further compound the issue), the length of tube.... in other
words, a lot of missing details. Some are suggestive in your use of
the term sleeve, but you don't provide much to help.

So I guess you would go coax center conductor to tube section #1,
braid to center of second coax through section #1 to section #2. Coax
from section #1 through section #2 to section #3 and so on?

So, what is #1, #2, #3, and so on? I get the impression you have a
vivid image of this in front of you, but you are blocking the view and
I can't see it.

73's
Richard Clark, KB7QHC

"Richard Clark" wrote in message
...
On Tue, 5 Feb 2008 15:06:40 -0800 (PST), Dave99
wrote:

OK thanks... Actually I was reading something that indicated you
should add in a velocity factor for the tube when using it as a
sleeve. I had never heard of that either, so I wasn't sure. They used .
95 I believe.

Hi Dave,

I presume you mean 0.95, which for a metal tube holding an inner
conductor that is air insulated, then that might be operative. Too
much is left unsaid: like frequency/wavelength, size of tube, any
inner conductor (so as to emulate a coax), any coax within the tube
(to further compound the issue), the length of tube.... in other
words, a lot of missing details. Some are suggestive in your use of
the term sleeve, but you don't provide much to help.

So I guess you would go coax center conductor to tube section #1,
braid to center of second coax through section #1 to section #2. Coax
from section #1 through section #2 to section #3 and so on?

So, what is #1, #2, #3, and so on? I get the impression you have a
vivid image of this in front of you, but you are blocking the view and
I can't see it.

73's
Richard Clark, KB7QHC

Hi Richard

Is it possible that dave is considering one of these
http://www.nodomainname.co.uk/Omnico...4collinear.htm ?

Jerry KD6JDJ

On Wed, 06 Feb 2008 01:54:21 GMT, "Jerry"
wrote:


"Richard Clark" wrote in message
.. .
On Tue, 5 Feb 2008 15:06:40 -0800 (PST), Dave99
wrote:

OK thanks... Actually I was reading something that indicated you
should add in a velocity factor for the tube when using it as a
sleeve. I had never heard of that either, so I wasn't sure. They used .
95 I believe.

Hi Dave,

I presume you mean 0.95, which for a metal tube holding an inner
conductor that is air insulated, then that might be operative. Too
much is left unsaid: like frequency/wavelength, size of tube, any
inner conductor (so as to emulate a coax), any coax within the tube
(to further compound the issue), the length of tube.... in other
words, a lot of missing details. Some are suggestive in your use of
the term sleeve, but you don't provide much to help.

So I guess you would go coax center conductor to tube section #1,
braid to center of second coax through section #1 to section #2. Coax
from section #1 through section #2 to section #3 and so on?

So, what is #1, #2, #3, and so on? I get the impression you have a
vivid image of this in front of you, but you are blocking the view and
I can't see it.

73's
Richard Clark, KB7QHC

Hi Richard

Is it possible that dave is considering one of these
http://www.nodomainname.co.uk/Omnico...4collinear.htm ?

Hi Jerry,

Now that you mention it, it does resemble the #1, #2, #3, and so on -
so described. This is also known as a Franklin Array, but not in the
classic design. Problem here is that the phasing of the radiating
elements' exteriors are critical to the operation of the antenna,
insofar as gain goes. On the other hand, the wavelength dimension of
the inside of the same elements are critical to the operation of the
antenna, insofar as matching goes. That the two electrical
wavelengths might match and possibly work is a guess as the author
states:
"we chose LMR-400 as it was lying on the floor"

The commercial builders of the same style antenna use simple wire with
the occasional spacer.

73's
Richard Clark, KB7QHC

On Feb 5, 3:06 pm, Dave99 wrote:
OK thanks... Actually I was reading something that indicated you
should add in a velocity factor for the tube when using it as a
sleeve. I had never heard of that either, so I wasn't sure. They used .
95 I believe.

So I guess you would go coax center conductor to tube section #1,
braid to center of second coax through section #1 to section #2. Coax
from section #1 through section #2 to section #3 and so on?

DD

If you are wanting to make a coaxial collinear using solid metal tube
(copper? aluminum?) for the elements, why not just make that tube the
outer conductor of coaxial sections. The inner conductor can be a
piece of solid copper wire, that then connects to the outer conductors
of the adjacent sections. Or maybe that's what you mean; it's not
really very clear to me.

Be aware that the phasing of the coaxial collinear is controlled by
the electrical length of the coaxial sections. For a "flat pancake"
pattern they should be an electrical half wave. Depending on the
insulation, that may be considerably shorter than a freespace half
wave. That does not directly matter to the antenna; non-resonant
antennas work just fine. The feedpoint impedance will be the parallel
combination of all the feedpoints (assuming low loss electrical half-
wave connecting sections), transformed by any coaxial stub between the
last feedpoint and the feedline. The "feedpoints" are all the gaps
between sections.

Cheers,
Tom

Sorry, I didn't give many details. My idea was basically for a
commercial band antenna that needs to cover a fairly wide range in the
5xx-4xx bands. I've had good performance using fairly large tubing for
wide bandwidth requirements on single element designs in the past, but
I've never attempted a multi element design using the same materials.
Lets say I'd be using 1 1/2" .065 aluminum tube. Testing would be
required to find the ideal length. Yes, I'm basically trying to see if
something along the lines of the web page plans posted above could be
utilized with a larger size tube. I just wasn't sure about how it
could be wired up. But looking at those plans, I think I see the way
it could be done. It would just take a lot of experimenting to get the
dimensions right.

Dave

On Wed, 6 Feb 2008 12:50:07 -0800 (PST), Dave99
wrote:

Yes, I'm basically trying to see if
something along the lines of the web page plans posted above could be
utilized with a larger size tube.

Above where?

73's
Richard Clark, KB7QHC

"Richard Clark" wrote in message
...
On Wed, 6 Feb 2008 12:50:07 -0800 (PST), Dave99
wrote:

Yes, I'm basically trying to see if
something along the lines of the web page plans posted above could be
utilized with a larger size tube.

Above where?

73's
Richard Clark, KB7QHC


I think he means http://www.nodomainname.co.uk/Omnico...4collinear.htm

(from Jerry's post in this thread)

John

On Wed, 06 Feb 2008 23:39:15 GMT, "John KD5YI"
wrote:

"Richard Clark" wrote in message
.. .
On Wed, 6 Feb 2008 12:50:07 -0800 (PST), Dave99
wrote:

Yes, I'm basically trying to see if
something along the lines of the web page plans posted above could be
utilized with a larger size tube.

Above where?

73's
Richard Clark, KB7QHC


I think he means http://www.nodomainname.co.uk/Omnico...4collinear.htm

(from Jerry's post in this thread)

Hi John,

I would think so to, but his verification is simpler than thinking for
myself. ;-)

73's
Richard Clark, KB7QHC

On Feb 6, 12:50 pm, Dave99 wrote:
Sorry, I didn't give many details. My idea was basically for a
commercial band antenna that needs to cover a fairly wide range in the
5xx-4xx bands. I've had good performance using fairly large tubing for
wide bandwidth requirements on single element designs in the past, but
I've never attempted a multi element design using the same materials.
Lets say I'd be using 1 1/2" .065 aluminum tube. Testing would be
required to find the ideal length. Yes, I'm basically trying to see if
something along the lines of the web page plans posted above could be
utilized with a larger size tube. I just wasn't sure about how it
could be wired up. But looking at those plans, I think I see the way
it could be done. It would just take a lot of experimenting to get the
dimensions right.

Dave

I really like the coaxial collinear design for relatively narrowband
work. The coaxial connecting stubs (whose outside surfaces are also
the radiating elements) keep the phasing locked down tightly.
Unfortunately for your application, that very advantage for narrowband
designs is a killer for broadband. That is, the pattern will change
from a "flat pancake" at the nominal design center frequency to a cone
up or down, above or below the design center frequency.

You can mitigate that to some extent by feeding the coaxial collinear
antenna in the center (with the feedline balanced and perpendicular to
the antenna axis for some distance) instead of at an end; in that
case, you can think of the pattern as a cone going one way for the
section above the feedpoint, and by symmetry, a cone going the
opposite direction for the section below, and the sum of the two
results in just a lowering of the gain--not so flat a pancake--when
operating off the design center frequency.

But a better way to do a broadband vertical collinear is to feed
several dipoles, stacked end-to-end (with some gap from one to the
next), each fed with the same electrical length of feedline, with the
far ends of all the feedlines paralleled. If the gap from one dipole
to the next is enough that the mutual impedances among the dipoles are
all small, then each dipole will have current very nearly in phase
with the others and the radiation pattern will be perpendicular to the
axis of the dipoles. It's a messier feed arrangement, but it's much
better for keeping the antenna currents in phase along the whole
antenna across a relatively wide frequency range.

Cheers,
Tom