"Roy Lewallen" wrote in message
...
wrote:
. . .
Now Roy I have a problem with what you are saying here
I spend hours modelling an array to lower the TOA or angle of max
radiation
which directly controls the main lobe dimension both in width and height.
And, as I've said quite a few times in one way or another, it's largely a
waste of time.
O.K. Roy let's get down to the nitty gritty and look at this question.
Your background in antenna programs makes you a person of choice
to declare if what I do is a waste of time and where I must default to an
experts judgement.
A month or so ago I gave a description of the antenna that I modelled
and for your interest I used the AOP program by Beasely a person
that you have collaborated with in the past.
One can design a yagi antenna with 8 elements say on a 60 foot boom
and then note the gain and the elevation angle of maximum gain.
This can be done using the most basic antenna program available.
The next step is to apply this same antenna to a program that is capable
of changing dimensions to obtain a desired function ,which in this case can
be
"Gain". There is reference to a NEC program on this group during the past
week
or so that I believe is capable of doing this, that is on the web and also
free to all.
With the use of variable dimensions which includes best x,y and Z positions
for various pulses or physical positions the program will procede to do as
asked.
This test is about as simple as it gets to show how the angle of max
radiation can be changed
as well as the envelope of the new angle range to achieve a 3 dB window of
radiation
You will see that the computor program will immediately remove itself
from a Yagi design to obtain a better gain and form an array that consists
of one driven element and where the rest are all reflectors!
Though the final shape appears to represent a dish it is not, it is simply a
design with multiple dimentional reflectors in the best coupling mode.
The result is a gain figure that will exceed the original design,
which is what we requested of the program i.e.allow it to make changes of
choice
to achieve a higher gain than the initial yagi design
With the above. one can change the elevation angle for maximum gain which
has now
dropped to a 11 to 10 degrees or even 9 degrees if one is willing to
sacrifice some gain.
This can be also be achieved by allowing the driven element to deviate from
a straight dipole
to a vee shape tipped in such away to helps control reactance swings of the
total array.
The above is quite simple to duplicate, where anybody can place a 8 element
yagi with a long boom
of 60 ft placed over real ground and challenge the program to devise a way
of increasing gain.
In my case the program changes to a non director mode without any prodding,
other programs
may well need some prodding. Changes to elevation for maximum gain will
change automatically
and one can expect to easily devise an array with a 10 degree angle where a
gain of 16 dbi is attained
as well as a broader lobe than can not be accomplished with a Yagi design.
If you find that you cannot repeat the above results in a short space of
time then it surely reflects
a misuse of programs on my part.
Please note that propagation has no part in forming the shape of the main
lobe to the
best of my understanding but you would know better than most as to what the
program parameters actually are
I look forward to your response or any other program users response that
shows my findings
are a waste of time so I can direct my experimentation in a more fruitfull
direction.
Best regards
Art
I model an antenna array such that it emulates in a way a "stacked"
array where as low as a 9/10 degree TOA. The 3 db gain window is broader
in width and narrower
in height than say the normal array. It is this "TOA" that determines
what window we have and
where it hits the ionesphere which thus determines its point of arrival
on the earths surface
snip
Is this the error of my ways where any change I make to an antennas
pattern
is rendered of no use because I must first find a way to manipulate
propagation
where all the action is really at?
. . .
Close. Sometimes two or more propagation modes are possible, such as
snip
any case, it doesn't matter how much I'm radiating at 1, 5, 7, or 15
degrees, or what my antenna's maximum angle is. All that counts is how
much I'm radiating at 3 or 12 degrees.
Snip
I also want to make it clear that I appreciate your post which I see as
an attempt to clarify matters
that are presently being discussed ie.It is propagation and not the
antenna that determines the
TOA. Or "antenna pattern is determined by propagation" so that we
don't get hung up
on the term TOA
snip
I suggest downloading the excellent, free, and easy to use propagation
software by Shel Shallon, W6EL, http://www.qsl.net/w6elprop/. In a few
minutes, you'll be able to see what angles are supported at a given time
and frequency for a given path.
Best regards
Art
Roy Lewallen, W7EL