"KE5MBX" wrote in message
oups.com...
I have been advised by some hams that the best way I can hope to do 10-
meters on my jeep is to mount my antenna ON THE WINDSHIELD to get a
good ground plane. I read somewhere since then that the primary
reason for cophasing CB antennas on trucks is NOT to direct the gain
front and back, but to even the ground plane as though the antenna
were in the center of the truck. Could I achieve the same effect with
my Jeep by cophasing antennas on either side of the jeep by the
doors? Even better- could I do this diagonally across from one corner
of my jeep to the other? I heard the further apart the antennas are,
the better, and I'm not really trying to get front/back gain for DXing.

What I did was purchase a 1/2 wave 11 meter whip from Radio shack and
trimmed it for 10m. Of course, for 1/2 wave you need not have a ground
plane, only a good ground point. I mounted it on the back bumper. It worked
very well on my Warngler.

On Feb 2, 9:35 pm, "Stefan Wolfe" wrote:
"KE5MBX" wrote in message

oups.com...

I have been advised by some hams that the best way I can hope to do 10-
meters on my jeep is to mount my antenna ON THE WINDSHIELD to get a
good ground plane. I read somewhere since then that the primary
reason for cophasing CB antennas on trucks is NOT to direct the gain
front and back, but to even the ground plane as though the antenna
were in the center of the truck. Could I achieve the same effect with
my Jeep by cophasing antennas on either side of the jeep by the
doors? Even better- could I do this diagonally across from one corner
of my jeep to the other? I heard the further apart the antennas are,
the better, and I'm not really trying to get front/back gain for DXing.

What I did was purchase a 1/2 wave 11 meter whip from Radio shack and
trimmed it for 10m. Of course, for 1/2 wave you need not have a ground
plane, only a good ground point. I mounted it on the back bumper. It worked
very well on my Warngler.

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?

"KE5MBX" wrote in message
ups.com...
On Feb 2, 9:35 pm, "Stefan Wolfe" wrote:
"KE5MBX" wrote in message

oups.com...

I have been advised by some hams that the best way I can hope to do 10-
meters on my jeep is to mount my antenna ON THE WINDSHIELD to get a
good ground plane. I read somewhere since then that the primary
reason for cophasing CB antennas on trucks is NOT to direct the gain
front and back, but to even the ground plane as though the antenna
were in the center of the truck. Could I achieve the same effect with
my Jeep by cophasing antennas on either side of the jeep by the
doors? Even better- could I do this diagonally across from one corner
of my jeep to the other? I heard the further apart the antennas are,
the better, and I'm not really trying to get front/back gain for DXing.

What I did was purchase a 1/2 wave 11 meter whip from Radio shack and
trimmed it for 10m. Of course, for 1/2 wave you need not have a ground
plane, only a good ground point. I mounted it on the back bumper. It
worked
very well on my Warngler.

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?

You are right of course...sorry...I didn't caculate the wavelength and was
merely making statements comparing the shorter "loaded" whip (forgetting it
was loaded), concluding the longer whip was 1/2 wave . However, I knew it
was 1/4 wave GP at the time and sometimes I just get afflicted with
oldtimers didease, complicated to exposure of high EM fields. :-)) The
unloaded 1/4 whip still worked well using the frame as a ground plane.

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