On 6 Feb 2005 05:42:42 -0800, wrote:


Here is the theoretical H-plane plot of our Yagi:

http://www.drslick.org/Temp1/yagiplot.jpg

And a photo:

http://www.drslick.org/Temp1/yagi929.jpg

After looking at the picture and the plot I fired up yo
and the only way I could get that low a gain was to
seriously mess up the antenna. The end effect was
a 2 element yagi witha spurious useless element.

This is further confirmed by the picture. It appears
the rightmost element is the fed element (very strange for a three
element design) and the proportions suggest a reflector close to the
driven and longer. The third element (the leftmost) would be spurious
as it's behind the reflector and far away.

Please explain that yagi, it's strange.

Allison

wrote:
On 6 Feb 2005 05:42:42 -0800, wrote:


Here is the theoretical H-plane plot of our Yagi:

http://www.drslick.org/Temp1/yagiplot.jpg

And a photo:

http://www.drslick.org/Temp1/yagi929.jpg

After looking at the picture and the plot I fired up yo
and the only way I could get that low a gain was to
seriously mess up the antenna. The end effect was
a 2 element yagi witha spurious useless element.

This is further confirmed by the picture. It appears
the rightmost element is the fed element (very strange for a three
element design) and the proportions suggest a reflector close to the
driven and longer. The third element (the leftmost) would be
spurious
as it's behind the reflector and far away.

Please explain that yagi, it's strange.


It was an unusual use of the YO
program, in that we used two reflectors
and NO directors, to get the shape we
wanted. We actually couldn't use the
optimizer, because it would actually
try to narrow the beam too much.
Remember that you must keep the
pattern about 180 degrees, and the F/B
ratio should be no more than about 11 dB.

If you could come up with something with
a higher overall dBi, i'd like to know,
but i doubt it.


Slick

On 6 Feb 2005 18:10:11 -0800, wrote:


snip


It was an unusual use of the YO
program, in that we used two reflectors
and NO directors, to get the shape we
wanted. We actually couldn't use the
optimizer, because it would actually
try to narrow the beam too much.
Remember that you must keep the
pattern about 180 degrees, and the F/B
ratio should be no more than about 11 dB.


Slick

Slick,
Could you explain the use of two reflectors? I've heard that if you
are building a two element yagi it's best to use a radiator and
reflector but haven't really learned anything about using more than
one reflector. Have seen antennas that use 3 reflectors, but they
were mounted perpendicular to the plane of the elements and there were
several director elements - if memory serves me it was Cushcraft that
did that. Haven't seen them added behind the first reflector and am
curious as to what characteristic of the antenna's performance it is
meant to enhance.

Thanks,
Howard
Howard

Howard wrote:
On 6 Feb 2005 18:10:11 -0800, wrote:


snip


It was an unusual use of the YO
program, in that we used two reflectors
and NO directors, to get the shape we
wanted. We actually couldn't use the
optimizer, because it would actually
try to narrow the beam too much.
Remember that you must keep the
pattern about 180 degrees, and the F/B
ratio should be no more than about 11 dB.


Slick

Slick,
Could you explain the use of two reflectors? I've heard that if you
are building a two element yagi it's best to use a radiator and
reflector but haven't really learned anything about using more than
one reflector. Have seen antennas that use 3 reflectors, but they
were mounted perpendicular to the plane of the elements and there
were
several director elements - if memory serves me it was Cushcraft that
did that. Haven't seen them added behind the first reflector and am
curious as to what characteristic of the antenna's performance it is
meant to enhance.


For this particular design, it was
required in that we needed something with a
180 degree pattern, and not to much F/B
ratio. I can't tell you much more other
than we had to manually tweak the variables
to get a decent result...we couldn't use the
program's optimizer, it would have made the
forward lobe too small.

So what ends up happening in the program,
is that you end up using two directors, but
in the H-plane the lobe goes to the rear (see
link). So in essence, you flip the whole
deal around, and your two directors are
actually reflectors. Interesting, eh?



Slick

On 6 Feb 2005 18:10:11 -0800, wrote:

Remember that you must keep the
pattern about 180 degrees, and the F/B
ratio should be no more than about 11 dB.

If you could come up with something with
a higher overall dBi, i'd like to know,
but i doubt it.

Want a list...

MOXON ( two)
Batwing
Asymetric array of dipoles
Phased array of vertical monopoles
Dipole against a plane relector
2 element Jpole yagi


Allison

wrote:
On 6 Feb 2005 18:10:11 -0800, wrote:

Remember that you must keep the
pattern about 180 degrees, and the F/B
ratio should be no more than about 11 dB.

If you could come up with something with
a higher overall dBi, i'd like to know,
but i doubt it.

Want a list...

MOXON ( two)
Batwing
Asymetric array of dipoles
Phased array of vertical monopoles
Dipole against a plane relector
2 element Jpole yagi



Remember that you must keep the
pattern about 180 degrees, and the F/B
ratio should be no more than about 11 dB.

I really doubt if you will
supply a link...


Slick

On 6 Feb 2005 21:19:41 -0800, wrote:

Asymetric array of dipoles
Phased array of vertical monopoles

Remember that you must keep the
pattern about 180 degrees, and the F/B
ratio should be no more than about 11 dB.

I really doubt if you will
supply a link...

www.andrews.com many of those commercial designs could be duplicated
and there are a few repeater builder sites that do exactly that.

Allison

wrote:
On 6 Feb 2005 21:19:41 -0800, wrote:

Asymetric array of dipoles
Phased array of vertical monopoles

Remember that you must keep the
pattern about 180 degrees, and the F/B
ratio should be no more than about 11 dB.

I really doubt if you will
supply a link...

www.andrews.com many of those commercial designs could be duplicated
and there are a few repeater builder sites that do exactly that.


???? That's a long distance
telephone service site...


Slick

On 7 Feb 2005 14:06:03 -0800, wrote:

???? That's a long distance
telephone service site...

http://www.andrew.com/products/antennas/

I added an "s" by error. Sheesh.

I figured you'd know their products as they are well known in
broadcast and VHF/UHF ham circles. However that was only one example.
There is also CellOne who also do antenna products and other useful
items. Of course there are only a few hundred (or more) companies
making antennas many of which are suited for a cartiod pattern work.

Allison

You can get just about any "theoretical" result if your theory is
adequately flawed. That's obviously the case here.

Roy Lewallen, W7EL