Actually, it is possible to lower the takeoff angle (the elevation angle
at which the pattern is maximum) without changing the antenna height.
The method is to narrow the free-space elevation radiation pattern. For
example, modify the EZNEC example file W8JK.ez by changing the height (Z
coordinates) to 0.5 wavelength. The takeoff angle is 25 degrees. Delete
one of the elements to make a dipole and note that the dipole's takeoff
angle is 28 degrees. The lowering is due to the substantially greater
elevation directivity of the W8JK. There aren't too many modestly sized
horizontal arrays that have enough elevation directivity to make much of
a difference in takeoff angle, however, so the difference is generally
small at best. It's also interesting to note that the takeoff angle of
this dipole over real ground is 2 degrees lower than the takeoff angle
of the dipole over perfect ground.

But as we and others have pointed out before, lowering the "takeoff
angle" (as the term is used by modeling programs) doesn't guarantee
better DX performance, and really doesn't mean much at all. For example,
the modified W8JK has a gain of 5.66 dBi at an elevation angle of 10
degrees and 0.31 dBi at 5 degrees. If we change source 2 phasing to -144
degrees for a nominally unidirectional pattern (see the recent
discussion about the impact of current distribution on front/back
ratio), the takeoff angle rises slightly to 26 degrees. But the gain at
10 degrees elevation is now 6.55 dBi and at 5 degrees 1.15 dBi, both
greater than the W8JK with its lower takeoff angle. And at very low
elevation angles, the gain of the dipole over real ground is very nearly
the same as the gain of the dipole over perfect ground, despite the
difference in takeoff angles. At higher angles, the dipole over perfect
ground is better, despite its higher takeoff angle.

Actual gain at elevation angles of around 2 to 10 or 12 degrees is a
valid and useful measure of DX performance; "takeoff angle" isn't. But
based on past performance, I'm not holding my breath that we'll be
seeing any actual numbers from Art about his innovations.

Roy Lewallen, W7EL

Wes Stewart wrote:
On Thu, 17 Mar 2005 04:13:02 GMT, "
wrote:




Yet at the same time many are anxious to find out how I managed
to lower the TOA. even in the face of presumed flawed analysis.
Weird. very weird yet again none declared it impossible



Perhaps my pestering you for the "secret" to lower "TOA" without
changing the antenna height was too oblique to qualify as "declaring
it impossible."

Therefore, let me as my congressman would say (actually not *my*
congressman, he's not that bright), "I would like to revise and expand
my remarks: It's impossible."