The elevation angle at which radiation is maximum (the "takeoff angle")
can be influenced by narrowing the free-space elevation pattern of the
antenna. A Yagi provides considerable directivity in the horizontal
direction, but not very much in the vertical direction. The elevation
pattern of the forward lobe of a Yagi doesn't look much different from
the elevation pattern of a dipole. Therefore, the elevation patterns of
a Yagi and dipole are very similar (except for very long Yagis, which do
begin to have some noticeable directivity in the elevation pattern). One
consequence of this similarity is that the gain of a Yagi over a dipole
in free space is about the same as the gain of a Yagi over a dipole at
any elevation angle when the two are mounted at the same height -- a
single number is adequate to describe the gain of a Yagi over a dipole,
no matter where the two are mounted (as long as they're at the same height).

There are some antennas that do compress the vertical pattern. One
notable antenna in this category is the W8JK. The result is that the
"takeoff angle" is lower for the W8JK than for a dipole at the same
height, and the gain of a W8JK compared to a dipole is different at
different elevation angles. I haven't looked at one in a long time, but
believe the "Lazy H" antenna also compresses the vertical pattern
somewhat, resulting in a lower "takeoff angle" than a dipole when
mounted over ground.

It's not too surprising that Art's antenna has the ability to compress
the vertical pattern somewhat, for the same general effect as the W8JK,
due to its physical geometry. This general characteristic of a lower
"takeoff angle" can be an advantage for working DX, so it might make the
constructional difficulties worthwhile for some people. The reduction in
F/B when maximizing gain also isn't surprising. I don't believe there's
any fundamental reason for this to always happen, but it's all too often
the case. Most arrays, both parasitic and driven, have relatively poor
F/B when adjusted for maximum gain. It becomes up to the user to decide
on the optimum tradeoff for his particular application.

Roy Lewallen, W7EL

art wrote:
Roy
After I mused a while on your post I then accepted it for the
unbiased
analysis that it was rather than a desired reflection of my own
thoughts.
It then drove me to consider chosing gain as the main criteria, after
all my interests
are talking to my mates in the U.K., but at the same time carrying on
with my main thought of moving away from the long boom analogy and its
accompanying gain aproach.
By adding a mast of 30 feet to accommodate additional elements rather
than extending boom length I was able to narrow the beam width to some
where in the 57 degree region but my excellent F/B that I obtained
earlier went way down. This was done by constructing elements in "V"
form with no restriction on alignment with respect to the driven
element other than the center of the elements must be close to the mast
i.e
to take advantage of low torque requirements.
With six elements on the 30 foot mast on the tower not only did the
gain increase
to 16 dbi ( others please take note of prior posts on this thread) but
the 'take off angle'
dropped to pretty close to !0 degrees ! This aproach for somebody who
wants to work DX seems a good way to go.
I now intend to pursue the aproach of letting the elements deviate
from the "V" shape to what I expect to be a parabolic shape, to
determine whether the extra work is worth while, as well as the
"ommission" of the most upper most element for when heavy static
occurrs.
What I really do find interesting is that one CAN get away from the
boom length aproach when seeking gain as well as obtaining a reasonable
impedance.
I also intend to attempt a tri band aproach as I move along, which may
take a while as my program has provision for a limited number variable
dimensions to optimize at one time and the number of dimensions in the
next model will certainly exceed 40 at a minimum, thus modelling cannot
be achieved in a single shot.
My present model, which moves me towards gain, seems to exceed what
performance I can expect compared to high F/B and is certainly opening
fresh avenues as to what type of antenna I will construct after the new
year.

Comments solicited from all........
and happy hollidays

Art