Dave Platt wrote:
I must admit a bit of scepticism in re Cecil's suggestion to use a
90-degree-phase-shifted endfire array feed... at least, for most car
and trucking applications. Granted, it'd give quite a bit of gain in
the forward direction... but at the expense of a deep null in the
rearward. It'd be great for speaking with the guy a few miles in
front of you... but you'd lose the ability to talk well with the guy a
few miles in back of you.

You would also lose interference from the rear. Simply
arrange a switched phase-shifting feedline that can aim
the beam forward or backward. It's like a Yagi mounted
on a motorhome.
--
73, Cecil http://www.w5dxp.com