Jeff Liebermann wrote:
On Fri, 07 May 2010 16:31:48 +0000, James186282
wrote:

My second question is in asking how effective is the typical rubber duck
antenna versus say a truly resonant antenna or even a 5/8th wave which
tries (if I understand it) to squish the pattern down from a sphere to a
doughnut so its hears and talks better out then "up and down"

If you start with a monopole, shortening the antenna in half with a
loading coil will result in half the gain or -3dB loss. 1/4th the
length is 1/4th the gain or -6dB loss. Etc. Shortening the antenna
doesn't change the pattern much. You still end up with roughly a
torus (donut) pattern. The torus is far from perfect and probably
resembles more of a sphere. Therefore, you don't have to worry much
about the loss of signal in the axial directions.

This isn't at all true generally. Shortening an antenna doesn't by
itself reduce the gain significantly -- less than 1/2 dB going from a
half wavelength dipole to an infinitesimally short one, due to change in
current distribution. Shorter antennas are typically less efficient than
longer ones due to loss in the matching components, whether those
components are in the form of a loading coil or some external matching
network, and ground loss if significant current flows through the
ground. And the amount of loss varies a great deal depending on the
components and other factors. Because of this, no firm number can be
attached to the change in efficiency or field strength with length, and
even approximate numbers should be viewed with suspicion.

A 5/8 wave antenna is the longest length (and therefore highest gain)
antenna that can be built before the antenna pattern starts to
resemble a cloverleaf (with deep nulls). The gain is about 1.5dB more
than a dipole. That's a fabulous 19% increase, which is kinda
marginal considering the added length.

The gain of a 5/8 wavelength radiator over a quarter wavelength under
ideal conditions is about 2.8 dB, not 1.5. The pattern is already
beginning to resemble a cloverleaf at this length, with a high-angle
lobe. But the high lobes aren't yet quite big enough to significantly
reduce the power in the main lobe, resulting in the gain. But this is
under ideal conditions, with perfect ground reflection. In an HT
environment, all bets are off. I personally use a half wavelength whip
on an HT, because its high end impedance minimizes current to the HT and
my body, leaving the whip itself to do most of the radiating.

. . .

Roy Lewallen, W7EL