"art" wrote
Back to the Vincent antenna, he has designed an antenna that is
shorter than that known before. .... The input impedance is an
advantage over similar antennas and at the same time not
requiring a ground plain without being a problem to the transmitter.
He is also radiating well in comparison to the height of antenna and
the radiating system has the appearance of being efficient.
___________

Probably you'll agree that good, new antenna designs need more
than "the appearance of being efficient." Let's expand on this..

The link below leads to a calculation of the system radiation efficiency and
r-f bandwidth of a conventional, 30-degree, base-loaded monopole, using the
equations found in standard antenna engineering texts. This is the physical
height used for the "standard DLM" antennas tested by the Navy for the
University of Rhode Island. The coil and r-f ground loss was set to 2 ohms,
total, to approximate the conditions in the U-RI test.

This non-DLM configuration of a short monopole has a system radiation
efficiency of about 59%, and for 1 kW of applied power generates an inverse
distance groundwave field of 241 mV/m at 1 km.

A standard, 1/4-wave vertical monopole with a matching network and r-f
ground loss of 2 ohms, total, is about 95% efficient, and for 1 kW of
applied power generates an inverse distance groundwave field of about 306
mV/m at 1 km.

So the field of the 30-degree radiator is about 2.07 dB below that of the
90-degree radiator -- and that is due mostly to the much lower radiation
resistance of the 30-degree radiator (about 2.9 ohms vs about 36 ohms)
against the 2 ohms of other losses in each system.

The March 31, 2005 U-RI test report states that the 3.5 MHz standard DLM had
a measured groundwave field at 1 mile that was 2.33 dB less than the Navy's
reference monopole (whose electrical height is not stated, but presumably is
90 degrees). So the measured h-plane gain of that DLM was about 0.26 dB
_less_ than a conventional, base-loaded, 30-degree monopole -- although that
difference could be within the range of measurement and/or modeling error.

Also note, Art, that the DLM needs a good r-f ground, just as do all
monopoles, and especially short ones. The Navy went to great effort to
provide a very good r-f ground and propagation path for the range where the
DLM was tested.

http://i62.photobucket.com/albums/h8...rtMonopole.gif

RF