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