Hey Peter, besides driving yourself nuts! BUY the ARRL Hand Book. You will
learn a lot from it.

Dennis Kaylor wrote in message . com...
i dont know why you cant seem to find what your looking for other than
your not wording the search right

Finding them is not the problem. Finding two that come even close to
giving the same dimensions is the problem (apart from ones that are
obvioulsy direct copies of a design on another site.)

I have already been to all the sites you listed and numerous others.
In fact the first one you listed is the same as the first one I
listed. The second one is no good because you have to be a member to
access any details. The third one is a quagi not a yagi and the 4th
one is one of those funny bow-tie types.

Most of the references you found most likely are giving you correct and
accurate numbers. The "ART" of antenna design is just that an art. When
you workup an antenna the variables are element length and element
spacing. The art is in adjusting these variables to achieve the results
you are looking for. I will not attempt to describe the iterations you
must go through to get it right, that's what the various texts are for.
Get the ARRL or RSGB books, either or both. The ARRL Antenna Book is one
of the best.

Good luck
Dave Nagel WD9BDZ

Peter wrote:
Dennis Kaylor wrote in message . com...

i dont know why you cant seem to find what your looking for other than
your not wording the search right


Finding them is not the problem. Finding two that come even close to
giving the same dimensions is the problem (apart from ones that are
obvioulsy direct copies of a design on another site.)

I have already been to all the sites you listed and numerous others.
In fact the first one you listed is the same as the first one I
listed. The second one is no good because you have to be a member to
access any details. The third one is a quagi not a yagi and the 4th
one is one of those funny bow-tie types.

.com...
i dont know why you cant seem to find what your looking for other than
your not wording the search right

Finding them is not the problem. Finding two that come even close to
giving the same dimensions is the problem (apart from ones that are
obvioulsy direct copies of a design on another site.)

Why should this be a problem?

Yagi-Uda antennas are complex beasts, due to the interactions between
the various elements. There is no single "best" design for all
uses... different designs are optimized for different parameters. If
you try to push the optimization quite hard in favor of one design
factor (e.g. maximum forward gain, or maximum front/back ratio) you're
likely to pay a price in terms of sub-optimal behavior in other
parameters (e.g. very narrow SWR bandwidth).

Many older Yagi-Uda designs were done by cut/try/measure methods.
More recent designs often take advantage of modern computer modelling
and optimization techniques, and can vary significantly from the older
designs. I would imagine that most (almost all?) of the published
designs meet their design goals pretty well, despite the differences
in the details of their construction.

Want a simple, direct-coaxial-attachment Yagi with a 50-ohm feedpoint
impedance? You can have one. Want a Yagi with a narrower element
spacing and lower feedpoint impedance which is conveniently matched
using a double-parallel-quarter-wave section of RG59? You can have
that, too. Want a ultra-short-beam Yagi to fit on a small roof and
not stick out into the neighbor's trees? You can have that, too.
These three different Yagi antennas will look rather different from
one another, since they're optimized for different goals.

So, you ought to first decide what you want, in an antenna... what the
importance of the various design parameters are. Then, choose a
decent design tool and go at it! Even better, try two or three
different design tools, and see how the resulting antennas model out.

Finally, build the darned thing, get on the air, and don't sweat that
last dB or so of gain or F/B ratio. "The best, is often the enemy of
the good" - if you focus too hard on having the Ultimate (Yagi, or
car, or whatever) you're likely to miss the pleasure of having a good
one to use, much sooner.

--
Dave Platt AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

peter
i dont understand your problem
all you have to do is pick one of the samples i send you and create the
antennas from the design make 3 or 4 of them and make them all alike
from one set of plans and you will be fine i would suggest building
something like the 432mhz one cause its closer to the freq you need
good luck
the next issue you will have is where to get the stuff to make the antenna

Peter wrote:
"I discovered that they (433 MHz yagi antennas) are around $179 here in
sydney and I need 3 of them so that ruled out buying them."

If Peter needs omnidirectional coverage, perhaps a vertical collinear
array is a good choice. These are found in many places, including the
ARRL Antenna Book, 19th edition, on pages 8-36 and 8-37. These produce a
moderate gain.

The Super-J Antenna on page 16-25 is another omnidirectional array with
a slight gain. Its advantage is its flexible matching arrangement.

Best regards, Richard Harrison, KB5WZI

Ok so there are lots of different designs that supposedly have
different strong points. Suppose I just want to go for maximum dB. How
do I achieve that? Does anyone have a site that explains what
parameters to use to achieve that?

And can anyone explain this. When I ran the DL6WU Antenna Design
Program and fed in my parameters (433.92MHz, 5mm thick elements,
plastic boom) it gave me a set of lengths and spacings and a supposed
dB of 12.1. But it had the DE and D1 3.4mm apart from centre to centre
meaning that with 5mm rod they were actually touching! I separated
them a bit and fed those lengths into Yagi Analysis 3.4 and it gave me
a dB of 4.9.

(Peter) wrote in message om...
Ok so there are lots of different designs that supposedly have
different strong points. Suppose I just want to go for maximum dB. How
do I achieve that? Does anyone have a site that explains what
parameters to use to achieve that?

You would want to build an "NBS" yagi if you want max gain and so-so
f/b.
There are many examples of these in the ARRL antenna handbook. They
have examples and specs for all vhf/uhf bands, also for differing
numbers of elements. All those examples for 432 use 3/16 inch element
dia. Element diameter is very critical to building a UHF beam. So that
means trying to design one on the puter is a waste of time, unless you
start out using the exact dia tubing you plan to use. This makes
scaling antennas from other bands with fatter tubing a pain. You will
likely end up with an oddball element dia if you scale a normal dia.
So its best to hunt down a good plan, and stick to it. Exactly.

And can anyone explain this. When I ran the DL6WU Antenna Design
Program and fed in my parameters (433.92MHz, 5mm thick elements,
plastic boom) it gave me a set of lengths and spacings and a supposed
dB of 12.1. But it had the DE and D1 3.4mm apart from centre to centre
meaning that with 5mm rod they were actually touching! I separated
them a bit and fed those lengths into Yagi Analysis 3.4 and it gave me
a dB of 4.9.

Dunno... Like I told Art Unwin a while back, I don't have much use for
antenna design programs and "optimizers" etc...Seems to me the vast
majority of the output is junk. I always get better results if I do it
all manually, and let common sense rule. But for UHF, I'd just find a
plan and use it. The examples in the ARRL antenna handbook are exactly
what you want. I don't know of any sources on the web. You can use
eznec demo and scale the "NBS yagi" it has, but then again you are
back to worrying about the element diameter scaling and whether any
real tubing will match what it spits out. The example is for 6m, and
using 1/2 inch tubing. No telling what that would scale to for 432
mhz. MK

"Mark Keith" wrote in message
om...
(Peter) wrote in message
om...
.. All those examples for 432 use 3/16 inch element
dia. Element diameter is very critical to building a UHF beam
.................................

Note that 3/16 is 4.76 mm, which is very close to his 5 mm. I would guess
any correction would be very minimal.

Tam/WB2TT

Peter wrote:
Ok so there are lots of different designs that supposedly have
different strong points. Suppose I just want to go for maximum dB. How
do I achieve that? Does anyone have a site that explains what
parameters to use to achieve that?

I hope not. If a long yagi is optimized for gain and nothing else, it is
usually quite poor in other respects: large sidelobes; narrowed,
sharp-pointed main lobe (hard to aim accurately); poor front/back ratio;
inconvenient feed impedance; poor gain and SWR bandwidths; and poor
tolerance to constructional dimensions, detuning by raindrops, frost
etc.

The same has been found many times over, whether you do it by
traditional cut-and-try or by computer - the computer only gets you to
the same dead-end faster.

Modern optimized yagis achieve almost the same gain, but don't have
those vices to anything like the same degree. They are much easier to
build, match and aim, so in practice you'll almost certainly achieve
*more* gain.


And can anyone explain this. When I ran the DL6WU Antenna Design
Program

There are dozens out there, but it's very clear you mean the one on my
site.

and fed in my parameters (433.92MHz, 5mm thick elements,
plastic boom) it gave me a set of lengths and spacings and a supposed
dB of 12.1. But it had the DE and D1 3.4mm apart from centre to centre
meaning that with 5mm rod they were actually touching!

You're so right - sorry, there was a bug.

That program had been reliably getting all the important things right
for about 20 years, but recently I blindly accepted someone else's
"correction" for a small error... which triggered an even larger error.

As of this message, the revised program is back on the site:
http://www.ifwtech.co.uk/g3sek/diy-yagi/

The bug only ever affected the shortest yagi that the program would
design... which was the one Peter wanted. Thanks for spotting it, Peter.


--
73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB)
Editor, 'The VHF/UHF DX Book'
http://www.ifwtech.co.uk/g3sek