Hello,

Does anyone know if there's a way to determine the velocity factor of
various metal tube types, diameters and gauges?

Also, on the same subject... Is there any reason why a collinear
couldn't be constructed from metal tubing pieces, in the same basic
method of a coax collinear?

Thanks for any help,

Dave

On Feb 5, 11:15 am, Dave99 wrote:
Hello,

Does anyone know if there's a way to determine the velocity factor of
various metal tube types, diameters and gauges?

Also, on the same subject... Is there any reason why a collinear
couldn't be constructed from metal tubing pieces, in the same basic
method of a coax collinear?

Thanks for any help,

Dave

I'm not sure just what you mean by "the velocity factor" of metal
tubes. Generally it's not the metal but the dielectric that
determines velocity factor.

But for sure you can construct a collinear from metal tubing pieces.
After all, coax is just a metal tube (which may be braided, foil or
solid) surrounding a center conductor.

Cheers,
Tom

K7ITM wrote:
On Feb 5, 11:15 am, Dave99 wrote:
Hello,

Does anyone know if there's a way to determine the velocity factor of
various metal tube types, diameters and gauges?

Also, on the same subject... Is there any reason why a collinear
couldn't be constructed from metal tubing pieces, in the same basic
method of a coax collinear?

Thanks for any help,

Dave

I'm not sure just what you mean by "the velocity factor" of metal
tubes. Generally it's not the metal but the dielectric that
determines velocity factor.

But for sure you can construct a collinear from metal tubing pieces.
After all, coax is just a metal tube (which may be braided, foil or
solid) surrounding a center conductor.

I suspect he means what length would be needed for a resonant quarter or
half wavelength. That's a function only of the diameter. You can find
graphs of a "shortening factor" for dipoles or some such in numerous
places such as the _ARRL Antenna Book_. Or you can get that information
very quickly and easily with the free EZNEC demo program from
http://eznec.com or with any other antenna modeling program.

Roy Lewallen, W7EL

"Roy Lewallen" wrote in message
...
K7ITM wrote:
On Feb 5, 11:15 am, Dave99 wrote:
Hello,

Does anyone know if there's a way to determine the
velocity factor of
various metal tube types, diameters and gauges?

Also, on the same subject... Is there any reason why a
collinear
couldn't be constructed from metal tubing pieces, in the
same basic
method of a coax collinear?

Thanks for any help,

Dave

I'm not sure just what you mean by "the velocity factor"
of metal
tubes. Generally it's not the metal but the dielectric
that
determines velocity factor.

But for sure you can construct a collinear from metal
tubing pieces.
After all, coax is just a metal tube (which may be
braided, foil or
solid) surrounding a center conductor.

I suspect he means what length would be needed for a
resonant quarter or half wavelength. That's a function
only of the diameter. You can find graphs of a "shortening
factor" for dipoles or some such in numerous places such
as the _ARRL Antenna Book_. Or you can get that
information very quickly and easily with the free EZNEC
demo program from http://eznec.com or with any other
antenna modeling program.

Roy Lewallen, W7EL


---------------


But in the end, you still have to cut the tube to the
electrical performance desired. Measurements only get you
into the ball park. But I know that you knew that. G


Ed, NM2K

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

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