"Richard Harrison" wrote:
The directive gain of an elementary doublet, assumed
to be infinitesimally short, is given as 1.5. A resonant
1/2-wave wire is given a gain of 1.64. The gain difference
between a tiny dipole and a 1/2-wave dipole is almost
insignificant. Certainly it is less than 1 dB.
______________

This is all true, of course, but might lead some to the invalid conclusion
that it also applies to monopoles (whips) of 1/2 wavelength or less working
against a ground plane, such as in mobile operations or back yard verticals.

When a vertical radiator works against a perfect ground plane, the
electrical length of that radiator effectively is doubled. So in reality an
electrical "1/4-wave vertical" has twice the gain of a *1/2-wave* dipole
because of the image effect of the ground plane, and the fact that all
radiation is confined to one hemisphere (above ground). Note in your quote
from Kraus, p 192 that the short monopole and the 1/4-wave monopole each
have 3dB more gain, respectively, than the free space elementary (short)
dipole and the 1/2-wave dipole he also lists there.

Using your statements above the line, one might think that it rather
pointless to use anything longer than a 1/4-wave vertical. But going from a
1/4-wave to a 1/2-wave vertical in fact will add ~1.6dB of gain at the peak
of the pattern envelope, and a 5/8-wave vertical will add almost 3dB. These
are worthwhile improvements in system performance. Broadcast engineering
consultants have recognized this, and used it to advantage for decades.

Better yet, get your own copy of Kraus. It`s in print and
well worth the price.

Good advice (I already have it).

RF