KE5MBX wrote:
Wow, that is some excellent information I didn't know.. that a 1/2
wave antenna doesn't need a ground plane. I looked it up and sure
enough, you're right! However, I'm sad to say that I really doubt
Radio Shack sells a 1/2 wavelength antenna for either 10 or 11
meters. The classic 102" whip, as I understand, is a 1/4 wavelength.
For a second I even considered putting a 2.5-meter (16.4 ft) whip on
my jeep, but I finally decided that really isn't practical. So, any
opinions on the cophasing of two 1/4 waves?

I have a GMC pickup with a three magnet magmount on top
of the cab and I use Hamsticks for 20m-10m. There's hardly
any noticeable difference when I move that magmount to
the hood of the pickup. Why not use a three magnet mag-
mount on your Jeep hood with a 10m Hamstick?

Do you have a roll bar on the Jeep? Lots of Jeep drivers
mount their CB antennas in the middle of the roll bar.
--
73, Cecil http://www.w5dxp.com

"Cecil Moore" wrote in message
t...
KE5MBX wrote:
Wow, that is some excellent information I didn't know.. that a 1/2
wave antenna doesn't need a ground plane. I looked it up and sure
enough, you're right! However, I'm sad to say that I really doubt
Radio Shack sells a 1/2 wavelength antenna for either 10 or 11
meters. The classic 102" whip, as I understand, is a 1/4 wavelength.
For a second I even considered putting a 2.5-meter (16.4 ft) whip on
my jeep, but I finally decided that really isn't practical. So, any
opinions on the cophasing of two 1/4 waves?

I have a GMC pickup with a three magnet magmount on top
of the cab and I use Hamsticks for 20m-10m. There's hardly
any noticeable difference when I move that magmount to
the hood of the pickup. Why not use a three magnet mag-
mount on your Jeep hood with a 10m Hamstick?

Do you have a roll bar on the Jeep? Lots of Jeep drivers
mount their CB antennas in the middle of the roll bar.
--
73, Cecil http://www.w5dxp.com

When I had my CJ I had a CB antenna mounted on a ball mount back behind the
rear wheel well.

In article ,
Cecil Moore wrote:

Do you have a roll bar on the Jeep? Lots of Jeep drivers
mount their CB antennas in the middle of the roll bar.

If the roll bar is thick enough, you can drill and tap it to mount the
whip directly. Then use a gamma match so you don't have to worry about
insulating the mount.

Fred
K4DII

On Sat, 03 Feb 2007 13:02:09 -0500, Fred McKenzie
wrote:

If the roll bar is thick enough, you can drill and tap it to mount the
whip directly. Then use a gamma match so you don't have to worry about
insulating the mount.

Hi Fred,

Gamma match the roll bar.

73's
Richard Clark, KB7QHC

Fred McKenzie wrote:
If the roll bar is thick enough, you can drill and tap it to mount the
whip directly. Then use a gamma match so you don't have to worry about
insulating the mount.

Just don't touch the roll bar. :-)
--
73, Cecil http://www.w5dxp.com

On Feb 3, 12:47 pm, Cecil Moore wrote:
Fred McKenzie wrote:
If the roll bar is thick enough, you can drill and tap it to mount the
whip directly. Then use a gamma match so you don't have to worry about
insulating the mount.

Just don't touch the roll bar. :-)
--
73, Cecil http://www.w5dxp.com

Thanks for all the ideas guys. I'm still really interested in the
cophasing thing. I have mounted a CB whip on the roll bar before, but
it has two disadvantages: Extreme height of the antenna and the
inability to close the soft top while the antenna's up. Could I not
cophase diagonally and therefore center the patten ?

KE5MBX wrote:
I'm still really interested in the
cophasing thing. I have mounted a CB whip on the roll bar before, but
it has two disadvantages: Extreme height of the antenna and the
inability to close the soft top while the antenna's up. Could I not
cophase diagonally and therefore center the patten ?

First a few thoughts. Co-phasing doubles the cost of
the antenna without outperforming a single whip (unless
the elements are separated by 1/4WL or more). So
why not a magmount on the hood with a single whip?
That would be my solution but I'm not very "cool". :-)
My contacts could not tell the difference between the
magmount on the roof of my pickup Vs on my hood.

Phasing would work best front-to-back. With 135 degree
phasing in elements separated by 1/8WL, a whopping 4 dB
gain is possible switchable from front to back. If 1/4WL
spacing is possible, bidirectional front and back gain
of 3.5 dB is possible with 180 degree phasing. If I were
driving an 18 wheeler, this is what I would do. Changing
the phasing to 90 degrees would give me a front or back
vertical beam.

There's no reason why your co-phasing idea will not work.
The feedpoint impedance of the two elements in parallel
will be 1/2 of the impedance of each element transformed
by the length of coax chosen. If you put the coax 'T' 1/4WL
back from each element, the impedance at that point should
be close to the feedpoint impedance of each element (assuming
35 ohms).
--
73, Cecil http://www.w5dxp.com

On Feb 3, 2:02 pm, Cecil Moore wrote:
KE5MBX wrote:
I'm still really interested in the
cophasing thing. I have mounted a CB whip on the roll bar before, but
it has two disadvantages: Extreme height of the antenna and the
inability to close the soft top while the antenna's up. Could I not
cophase diagonally and therefore center the patten ?

First a few thoughts. Co-phasing doubles the cost of
the antenna without outperforming a single whip (unless
the elements are separated by 1/4WL or more). So
why not a magmount on the hood with a single whip?
That would be my solution but I'm not very "cool". :-)
My contacts could not tell the difference between the
magmount on the roof of my pickup Vs on my hood.

Phasing would work best front-to-back. With 135 degree
phasing in elements separated by 1/8WL, a whopping 4 dB
gain is possible switchable from front to back. If 1/4WL
spacing is possible, bidirectional front and back gain
of 3.5 dB is possible with 180 degree phasing. If I were
driving an 18 wheeler, this is what I would do. Changing
the phasing to 90 degrees would give me a front or back
vertical beam.

There's no reason why your co-phasing idea will not work.
The feedpoint impedance of the two elements in parallel
will be 1/2 of the impedance of each element transformed
by the length of coax chosen. If you put the coax 'T' 1/4WL
back from each element, the impedance at that point should
be close to the feedpoint impedance of each element (assuming
35 ohms).
--
73, Cecil http://www.w5dxp.com

Excellent.. If I put my antennas on opposite corners of the Jeep as I
was thinking, I find that they will be 4.2 meters apart. I promise to
go home and see what the ARRL handbook says about cophasing, but I
only understood what you just told me partially. Are you describing a
way to get better front/back gain from a system with one antenna in
front and one in back, as opposed to the conventional "trucker"
setup? I have no particular use for directional gain on 10 meters, by
the way.

I know a lot of people are reluctant to do the superior front-to-back
cophasing because it looks goofy, but I can assure I'm not interested
in being "cool" either! I want the most efficient 10-m operation I
can get out of a Jeep Wrangler.

"KE5MBX" wrote in message
ups.com...
On Feb 3, 2:02 pm, Cecil Moore wrote:
KE5MBX wrote:
I'm still really interested in the
cophasing thing. I have mounted a CB whip on the roll bar before, but
it has two disadvantages: Extreme height of the antenna and the
inability to close the soft top while the antenna's up. Could I not
cophase diagonally and therefore center the patten ?

First a few thoughts. Co-phasing doubles the cost of
the antenna without outperforming a single whip (unless
the elements are separated by 1/4WL or more). So
why not a magmount on the hood with a single whip?
That would be my solution but I'm not very "cool". :-)
My contacts could not tell the difference between the
magmount on the roof of my pickup Vs on my hood.

Phasing would work best front-to-back. With 135 degree
phasing in elements separated by 1/8WL, a whopping 4 dB
gain is possible switchable from front to back. If 1/4WL
spacing is possible, bidirectional front and back gain
of 3.5 dB is possible with 180 degree phasing. If I were
driving an 18 wheeler, this is what I would do. Changing
the phasing to 90 degrees would give me a front or back
vertical beam.

There's no reason why your co-phasing idea will not work.
The feedpoint impedance of the two elements in parallel
will be 1/2 of the impedance of each element transformed
by the length of coax chosen. If you put the coax 'T' 1/4WL
back from each element, the impedance at that point should
be close to the feedpoint impedance of each element (assuming
35 ohms).
--
73, Cecil http://www.w5dxp.com

Excellent.. If I put my antennas on opposite corners of the Jeep as I
was thinking, I find that they will be 4.2 meters apart. I promise to
go home and see what the ARRL handbook says about cophasing, but I
only understood what you just told me partially. Are you describing a
way to get better front/back gain from a system with one antenna in
front and one in back, as opposed to the conventional "trucker"
setup? I have no particular use for directional gain on 10 meters, by
the way.

I know a lot of people are reluctant to do the superior front-to-back
cophasing because it looks goofy, but I can assure I'm not interested
in being "cool" either! I want the most efficient 10-m operation I
can get out of a Jeep Wrangler.


Just go with one antenna.