Assuming one whip is pointing up, which way is the other whip pointing?

The way I saw it done, the other whip was at the other end of the car
and also pointing up. I have no knowledge of whether this was actually
useful, but apparently the user thought it was.

In which case, it is a phased vertical array, not a dipole. With
a spacing of 1/8WL, one can get 4 dB gain that way.
--
73, Cecil http://www.qsl.net/w5dxp



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.

73,
Kevin, WB2EMS