"Roy Lewallen" wrote in message
...
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.

That is exactly what I pointed to in the discussion. The top half of the
forward
lobe of a directive array is of no use say for opening a band. The important
point
is the underside contour of the main lobe where there is useful gain at the
angles
that Roy stated. For instance; a 60 foot + boom yagi with a gain of around
16 dbi
will have a TOA at say 13 degrees but it is also possible to construct a
directive array
of 10 degrees TOA that has the same underside contour as the yagi design and
thus equal
in performance. The difference is that a yagi design has a fat lobe with
narrow beam width,
where asyou can construct a radiator or an array that has a larger beam
width,
but with a thinner lobe that covers the aforementioned degrees of coverage
required.
Another point of mention is that many associate low TOA with antenna height
but
without specificity with respect to feed point height or as in other cases
such as a top hat or "unused" array as with stacked antennas
For me it is a question of phase angle provided by a transmitting point
where its optimum angle is directly opposite the earths surface and
supplimented
by a secondary radiation of a similar phase, but to explain why
would be impossible with respect to this group so don't ask

One particular poster hit things right on the head when he referred to
resistive impedance
THRU OUT the length of any radiator./s, he obviously knows his stuff tho I
question
the thin wire aproach to accomplish this i.e. negate reactance



But
based on past performance, I'm not holding my breath that we'll be seeing
any actual numbers from Art about his innovations.



Just for me, try to hold your breath for ten minuits.
You well know that no figures are accepted by the know
alls on this group. Even observed tests undertaken are not accepted unless
the so called guru is actually present which would be impossible , since the
gurus
wish is to preserve their perceived stations and not subject to ridicule
On this actual thread I have given explanations and figures and only
ommited how I achieve it ,which I will save until I have completed pertinent
studies.
As a former engineer which apparently you say that you are one also, it is
important
to review and check your work several times to ensure that it is in
presentable state
to fellow engineers for review. One says that it is impossible, another
somehow
turns his responses to unfounded gibberish and another declares the whole
thing as hillarious and so on, such that any comment made, even when made
in approval,
is meaningless as comments made are emotional and without any technical
depth.
Art Unwin KB9MZ..............XG



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."