F. Feeney wrote:
Actually, I read about this in Don Johnson of Screwdriver antenna fame's
book on mobile radio operation. IIRC, the folks experimenting with it
put the second whip on the far end of the car - tied to the frame, ie
grounded - not driven. When tuned to resonance an increase in RF current
in the car body was noticed and I think they also saw about a 3db
increase in radiated signal. I imagine it's not very popular because of
the difficulty of tuning two antennas instead of one, and the visual
aspect of a second large antenna on the vehicle. It just isn't that
practical even for a 3 db increase in signal.

It wasn't presented as being a dipole or any form of phased array. Just
as empirical data that picked up along the way that was interesting.

It would be a vertical beam with the boom (vehicle) capacitively
coupled to ground. It would work best on 10m-11m but should work
pretty well all the way down to 14 MHz. Probably not very useful
except for stationary use.

Actually, I experienced the same effect from a rear bumper mounted
screwdriver on my pickup. At the frequency where the truck is 1/4WL,
I experienced considerable gain in the direction the front of the
truck was pointed compared to off the sides of the truck. On one
Alaska contact from Arizona, it made the difference in being able
to carry on a QSO or not. It was a V-beam effect.
--
73, Cecil, W5DXP