Just curious, what is the result of computer modeling for the ideal
shape of Yagi elements? I couldn't just be simple tubes.

On Wed, 31 Mar 2004 11:40:23 +0800, Dan Jacobson
wrote:
Just curious, what is the result of computer modeling for the ideal
shape of Yagi elements? I couldn't just be simple tubes.

Hi Dan,

Been a long time since I've heard anyone described as totally tubular,
much less simple tubes....

Anyway, RF current is pretty much confined to the outermost layer of
metal for any conductor ( skin effect). On the basis of weight and
cost reduction, there is no merit in using solid rods when you move on
out of the common wire dimensions. In other words, the missing metal
hardly contributed to lower resistance for RF.

73's
Richard Clark, KB7QHC

"Richard Clark" wrote in message
...
On Wed, 31 Mar 2004 11:40:23 +0800, Dan Jacobson
wrote:
Just curious, what is the result of computer modeling for the ideal
shape of Yagi elements? I couldn't just be simple tubes.

Hi Dan,

Been a long time since I've heard anyone described as totally tubular,
much less simple tubes....

Anyway, RF current is pretty much confined to the outermost layer of
metal for any conductor ( skin effect). On the basis of weight and
cost reduction, there is no merit in using solid rods when you move on
out of the common wire dimensions. In other words, the missing metal
hardly contributed to lower resistance for RF.

73's
Richard Clark, KB7QHC

How about a taper that puts the biggest diameter where the current is
greatest.

Tam/WB2TT

Quite a few years ago, there were a couple of articles -- in Ham Radio
magazine, I believe --, which addressed that topic. As I recall, the
author used an optimization program that allowed the shape to vary. He
ended up with elements bent kind of like a gull wing, and considerably
longer than a half wavelength -- more like a wavelength if I recall
correctly. The gain was substantially more than for a Yagi, but I don't
remember how good the F/B ratio was. I believe he did construct and
measure some actual antennas.

I'm sorry I don't recall the name of either the author or the articles.
Hopefully, though, this posting will spur someone with a better memory
(and that includes just about everyone) to recall and report enough
information for you to find the articles.

The articles were very interesting, but it looked to me like the
construction problems would outweigh the benefits. Apparently I'm not
the only one to reach that conclusion, because in the intervening years
I've never seen an actual antenna resembling that design.

Roy Lewallen, W7EL

Dan Jacobson wrote:

Just curious, what is the result of computer modeling for the ideal
shape of Yagi elements? I couldn't just be simple tubes.

In article ,
Roy Lewallen wrote:

Quite a few years ago, there were a couple of articles -- in Ham Radio
magazine, I believe --, which addressed that topic. As I recall, the
author used an optimization program that allowed the shape to vary. He
ended up with elements bent kind of like a gull wing, and considerably
longer than a half wavelength -- more like a wavelength if I recall
correctly. The gain was substantially more than for a Yagi, but I don't
remember how good the F/B ratio was. I believe he did construct and
measure some actual antennas.

I think you're referring to the Landstorfer-Sacher Yagi design?

http://www.cebik.com/eb.html has some information on these. It's
something akin to an EDZ (extended double zepp) beam. A 2-meter
3-element L-S Yagi shows gain in the 9.7 dB range, with F/B ratios of
16-23.

Interesting design. Not the easiest thing in the world to construct,
I suspect.

--
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!

That name sounds familiar, so it's probably the one. Unfortunately, the
picture boxes at that web page appear blank using either IE6 or Mozilla
1.6, so I can't tell for sure. Must need some kind of plug-in to view them.

Roy Lewallen, W7EL

Dave Platt wrote:

In article ,
Roy Lewallen wrote:


Quite a few years ago, there were a couple of articles -- in Ham Radio
magazine, I believe --, which addressed that topic. As I recall, the
author used an optimization program that allowed the shape to vary. He
ended up with elements bent kind of like a gull wing, and considerably
longer than a half wavelength -- more like a wavelength if I recall
correctly. The gain was substantially more than for a Yagi, but I don't
remember how good the F/B ratio was. I believe he did construct and
measure some actual antennas.


I think you're referring to the Landstorfer-Sacher Yagi design?

http://www.cebik.com/eb.html has some information on these. It's
something akin to an EDZ (extended double zepp) beam. A 2-meter
3-element L-S Yagi shows gain in the 9.7 dB range, with F/B ratios of
16-23.

Interesting design. Not the easiest thing in the world to construct,
I suspect.

thats likely the one. i have their book 'optimisation of wire antennas'
that derives a design that sounds like that one.

"Roy Lewallen" wrote in message
...
That name sounds familiar, so it's probably the one. Unfortunately, the
picture boxes at that web page appear blank using either IE6 or Mozilla
1.6, so I can't tell for sure. Must need some kind of plug-in to view
them.

Roy Lewallen, W7EL

Dave Platt wrote:

In article ,
Roy Lewallen wrote:


Quite a few years ago, there were a couple of articles -- in Ham Radio
magazine, I believe --, which addressed that topic. As I recall, the
author used an optimization program that allowed the shape to vary. He
ended up with elements bent kind of like a gull wing, and considerably
longer than a half wavelength -- more like a wavelength if I recall
correctly. The gain was substantially more than for a Yagi, but I don't
remember how good the F/B ratio was. I believe he did construct and
measure some actual antennas.


I think you're referring to the Landstorfer-Sacher Yagi design?

http://www.cebik.com/eb.html has some information on these. It's
something akin to an EDZ (extended double zepp) beam. A 2-meter
3-element L-S Yagi shows gain in the 9.7 dB range, with F/B ratios of
16-23.

Interesting design. Not the easiest thing in the world to construct,
I suspect.

http://www.cebik.com/eb.html has some information on these. It's
something akin to an EDZ (extended double zepp) beam. A 2-meter
3-element L-S Yagi shows gain in the 9.7 dB range, with F/B ratios of
16-23.

That name sounds familiar, so it's probably the one. Unfortunately, the
picture boxes at that web page appear blank using either IE6 or Mozilla
1.6, so I can't tell for sure. Must need some kind of plug-in to view them.

Weird! They show up fine on my Linux workstation using Mozilla 1.5
and on my laptop using Mozilla Firefox 0.8. I saved on of the images
to disk, and it proved to be a very ordinary GIF file, with only two
colors. They ought to be visible in any standard browser.



--
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!

I contacted LB about the problem, and he said he'd received reports
similar to mine. He's contacted the web host but hasn't heard back yet.
So it's being addressed.

My browsers are both standard as far as I can determine. My firewall is
set to a pretty touchy level, though, so that might be the cause. But I
haven't had trouble with pictures at other sites.

Roy Lewallen, W7EL

Dave Platt wrote:

http://www.cebik.com/eb.html has some information on these. It's
something akin to an EDZ (extended double zepp) beam. A 2-meter
3-element L-S Yagi shows gain in the 9.7 dB range, with F/B ratios of
16-23.


That name sounds familiar, so it's probably the one. Unfortunately, the
picture boxes at that web page appear blank using either IE6 or Mozilla
1.6, so I can't tell for sure. Must need some kind of plug-in to view them.


Weird! They show up fine on my Linux workstation using Mozilla 1.5
and on my laptop using Mozilla Firefox 0.8. I saved on of the images
to disk, and it proved to be a very ordinary GIF file, with only two
colors. They ought to be visible in any standard browser.

Dan Jacobson wrote:
"Just curious, what is the result of computer modeling for the ideal
shape of Yagi elements?"

Advantage of a Yagi is gain in a small space due to close element
spacing. This also results in lower radiation resistance as the size
goes down with increased coupling and gain. To get a more convenient
Yagi drivepoint impedance (5 ohms is not usually convenient), a folded
dipole is often used as the driven element. That can multiply the
impedance by 4. See "Multi-Element V-H-F Beam Antennas" section of
Editors and Engineers "The Radio Handbook", William I. Orr, W6SAI,
Editor 15th Edition.

The tapered elements, large at the boom and small at the tip as shown in
the "ARRL Antenna Book", are mechanically sound but the taper is the
reverse of that needed for wide bandwidth.

Cones which grow in size from feedpoint to open ends have an advantage
of more uniform characteristic impedance.

Kraus says on page 229 of his 1950 edition:
"Whereas the characteristic impedance of a biconical antenna is uniform,
the impedance of antennas of shapes other than conical is nonuniform."

Terman says on page 921 of his 1955 edition:
"A particularly effective manner of utilizing the thick antenna
principle to obtain a wideband is to employ a cone antenna. Excitation
at the apex starts a spherical wave, as illustrated in Fig. 23-56, which
spreads out along the cone and in adjacent space without reflection
until reaching the end of the cone."

I don`t know what a computer program indicates as an ideal shape for a
Yagi`s driven element. The conical element shape may be a candidate for
computer optimization. Kraus and Terman have suggestions about the apex
angle and length of the cone.

Best regards, Richard Harrison, KB5WZI