Hi, I am looking to build an antenna for CB band... It will be going up
in my attic with about a 19 foot ceiling. I would like to have it free
standing as I have no way to get to the top to hang a wire type
antenna...

here is what I was thinking of doing:

I was going to biuld a 1/2 dipole but out of 1/2" copper pipe using PVC
pipe as insulators for the center and bottom and building some kind of
wood base for it.

will this work the same as a 12g wire dipole? do I still make each
side 8' 5" long or will this change? Does it matter what side is up?
any tips or ideas?

thanks
Jim

On 22 Dec 2005 18:45:44 -0800, wrote:

Hi, I am looking to build an antenna for CB band... It will be going up
in my attic with about a 19 foot ceiling. I would like to have it free
standing as I have no way to get to the top to hang a wire type
antenna...

here is what I was thinking of doing:

I was going to biuld a 1/2 dipole but out of 1/2" copper pipe using PVC
pipe as insulators for the center and bottom and building some kind of
wood base for it.

will this work the same as a 12g wire dipole? do I still make each
side 8' 5" long or will this change? Does it matter what side is up?
any tips or ideas?

thanks
Jim


Don't waste your money on copper pipe. 12 or 14 gauge wire will work just fine.

You can also build a 1/4 ground plane, and stick it on a 9 or 10 foot mast.

Vinnie S.

On 22 Dec 2005 18:45:44 -0800, wrote:

Hi, I am looking to build an antenna for CB band... It will be going up
in my attic with about a 19 foot ceiling. I would like to have it free
standing as I have no way to get to the top to hang a wire type
antenna...

here is what I was thinking of doing:

I was going to biuld a 1/2 dipole but out of 1/2" copper pipe using PVC
pipe as insulators for the center and bottom and building some kind of
wood base for it.

will this work the same as a 12g wire dipole? do I still make each
side 8' 5" long or will this change? Does it matter what side is up?
any tips or ideas?

thanks
Jim


Jim,

Here is the site for the homemade 1/4 ground plane. The pipe would work better
here. So would rigid solid copper wire. I think this is a better option for
local talking. The dipole would work better for DX.

Whatever you do, keep it the hell away from any kind of romex or AC wiring. It
will induce some noise. I had a similar problem because of that. But you are
better off with a 19 foot attic. Get the antenna tip to the top of the roof.

Vinnie S.

Vinnie S. wrote:
On 22 Dec 2005 18:45:44 -0800, wrote:


Hi, I am looking to build an antenna for CB band... It will be going up
in my attic with about a 19 foot ceiling. I would like to have it free
standing as I have no way to get to the top to hang a wire type
antenna...

here is what I was thinking of doing:

I was going to biuld a 1/2 dipole but out of 1/2" copper pipe using PVC
pipe as insulators for the center and bottom and building some kind of
wood base for it.

will this work the same as a 12g wire dipole? do I still make each
side 8' 5" long or will this change? Does it matter what side is up?
any tips or ideas?

thanks
Jim



Jim,

Here is the site for the homemade 1/4 ground plane. The pipe would work better
here. So would rigid solid copper wire. I think this is a better option for
local talking. The dipole would work better for DX.

Whatever you do, keep it the hell away from any kind of romex or AC wiring. It
will induce some noise. I had a similar problem because of that. But you are
better off with a 19 foot attic. Get the antenna tip to the top of the roof.

Vinnie S.

The unbalanced 1/4 wave GP will match to the CB better then a balanced dipole.

Coax is unbalanced. It's a hot and a shield. Dipoles need equal and opposite feed.

You need about 8.6 feet per element.

http://www.monsterfm.com/engineering/antcalc.htm

I built the yagi at arrl.org, 7db for 7 bucks.
Works damn good for being made of coat hangers and a 1x2!

I tried to build CB antennas. They are BIG. 2 meter antennas are much smaller.
VHF-FM has much better local range then 11 meters. I use part 95 and 97 all the time.

I may have to try one of these for 2 meters and another for 430 MHz ATV.
http://www.softcom.net/users/kd6dks/quad.html

Yagis are simpler to build, but I'm told quads have better gain.
Quagis have quad feeds and yagi elements. I need to bug Jay for
some good matches for coax to balanced feed units.

Another ham mentioned that the shorter director is capacitive
and the longer reflector is inductive. The lead/lag of the
elements causes the waves to constructively add in one direction
more then others.

On Fri, 23 Dec 2005 01:15:07 -0500, Scott in Baltimore
wrote:

The unbalanced 1/4 wave GP will match to the CB better then a balanced dipole.

Coax is unbalanced. It's a hot and a shield. Dipoles need equal and opposite feed.

You need about 8.6 feet per element.


We need to find out what he is going to use it for. I would probably go with the
1/4 GP mounted on a PVC mast. That would be about 8 feet off his attic floor.
Might work pretty well.

I has a Starduster in the attic in 1983, and did OK. This will work better that
the Starduster.


Vinnie S.

I am really looking for mainly local talking...

vinnie I don't think you included the web address for the 1/4 GP
antenna...

On 23 Dec 2005 13:30:15 -0800, wrote:

I am really looking for mainly local talking...

vinnie I don't think you included the web address for the 1/4 GP
antenna...


Crap. Sorry about that. Usethe 1/4 ground plain.

http://home.att.net/~wizardoz/cbmw/a...i.html#groundp


Remember to cut the center radial long, and trim shorter to adjust SWR. Mount it
on a plastic mast like PVC or ABS. It does not have to be metal since it's
indoors, and there is no wind ot weather. Get the tip as high as possible.

Also, use a 1:1 balun so the coax doesn't radiate. Basically, that is a fancy
term for coiled coax, which should be place just before the feedpoint.

Here is a site to help:

http://www.hamuniverse.com/balun.html

When I built mine, I used two PVC 4 inch couplers glued together. And I wrapped
the coax around it, tying it down with ty-raps. If you need pictures, I can send
them. The purpose of this coil is to choke RF so the coax does not act as a
ground radial or part of the antenna. That is also why it's place as close to
the feed as possible.



Vinnie S.

pics would help I am a visual person... does the ground plane have to
be put at a 45d angle?

On 23 Dec 2005 14:15:11 -0800, wrote:

pics would help I am a visual person... does the ground plane have to
be put at a 45d angle?

I don't think so, only because I have seen flat ground planes. My Starduster
were at a sharp angle. Maybe Scott can knows better. I would think the flat or
GP at 90 degrees to the center conductor is fine.

BTW, since you are running it indoors, use Belden 9913 coax. It is more flexible
than LMR400 or such.


Vinnie S.

I don't think so, only because I have seen flat ground planes. My Starduster
were at a sharp angle. Maybe Scott can knows better. I would think the flat or
GP at 90 degrees to the center conductor is fine.

Straight radials would create a 30 ohm antenna.
45 degree droops create about 50 ohms.

There shouldn't be any current flowing down the outside of the
shield with a groundplane, so you won't need a balun,
unlike a dipole that requires equal and opposite phases.
If you try to feed a dipole with coax, the outer shield
becomes part of the antenna system, causing high SWR readings,
(even if the SWR is low), RF interference and degraded performance.