SUPER J-POLE BEATS YAGI BY 1 dB
 

Hi,

Well, our Super J-pole:
http://users.marktwain.net/aschmitz/...jpolecalc.html


Is beating our Yagi in ALL directions,
even in the forward lobe!


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



So if you assume the theoretical
2.5 dBi of a regular J-pole, then the Super
J-pole has about 3 dB over that, so about
5.5 dBi all around.

So we have about 4.52 dB in the
forward lobe of our Yagi, so even there,
we beat it by about 1 dB with the Super
J-pole. That's like 238 watts versus
300 watts.
It's even worse in the back
lobe, where it's a -12 dB difference.
That's like 19 watts versus 300 watts!

It's only a theoretical
yagi optimization plot, and i don't think
it sounded like 19 versus 300 watts in the
back, but it's a BIG difference, even in the
areas that were already strong....almost
full quieting.

And yeah, we didn't really optimize
the yagi for a strong, narrow lobe...it was
designed for a 180 degree pattern, so the
gain ain't great, but you still have some
control over directivity. It's still
not really a fair comparison.

At any rate, if you need an
omnidirectional, i highly recommend the
Super J-pole!

Here's another site if you are
interested:

http://www.geocities.com/n2uhc/jpole.html


Questions and comments appreciated!

Dr. Slick

wrote

Well, our Super J-pole:
Is beating our Yagi in ALL directions,
even in the forward lobe!
____________________

Please explain how this design is directional. It should be essentially
omnidirectional in the horizontal plane, unless it is side-mounted on a
vertical metallic support, or has some other form of v-pol parasitic
radiator near it.

And in that case, it's not your j-pole alone that is "beating" a yagi, but
the combination of your j-pole and its mounting environment.

RF

Visit http://rfry.org for FM transmission system papers.

Dr. Slick,
It's fun to play with numbers, isn't it? you can
make them say almost anything you want if you "assume"
just one or two small points...
'Doc

Hi,

Well, our Super J-pole:
http://users.marktwain.net/aschmitz/...jpolecalc.html


Is beating our Yagi in ALL directions,
even in the forward lobe!
much snippage

Must be one horridly poor yagi. Most 3 eleemnt designs are better
than 8dBi and with a little effort an be 1 db better than that.

Most Stacked Jpoles do not perform as well as predicted on paper with
the upper added dipole contributing .5 to 1 db less than guessed at.

Allison

Allison wrote:
much snippage


Must be one horridly poor yagi. Most 3 eleemnt designs are better
than 8dBi and with a little effort an be 1 db better than that.

Most Stacked Jpoles do not perform as well as predicted on paper with
the upper added dipole contributing .5 to 1 db less than guessed at.

Allison

Not to mention, also, that that yagi is tuned to 92.9 MHz (in the FM
BROADCAST BAND)! --Jim NN7K

On Sun, 06 Feb 2005 17:56:25 GMT, Jim - NN7K
wrote:

Not to mention, also, that that yagi is tuned to 92.9 MHz (in the FM
BROADCAST BAND)! --Jim NN7K

Yes, that will really help. ;-p

I'd add the picture I looked at appeared to have a metal mast mounting
a vertical oriented beam and my experience at VHF and up is that hurts
performance.

All the years of building and testing says, extroadinary claims are
simply that. It's interesting to check the CSVHF range tests of
antennas on real antennas seperate from their sometimes fanciful
claims.

Allison
KB1GMX

wrote:
On Sun, 06 Feb 2005 17:56:25 GMT, Jim - NN7K
wrote:

Not to mention, also, that that yagi is tuned to 92.9 MHz (in the FM
BROADCAST BAND)! --Jim NN7K


yes, indeed it is!!



Yes, that will really help. ;-p

I'd add the picture I looked at appeared to have a metal mast
mounting
a vertical oriented beam and my experience at VHF and up is that
hurts
performance.


We modeled the mast in the position it's in,
and changing the length doesn't affect the pattern
significantly.


All the years of building and testing says, extroadinary claims are
simply that. It's interesting to check the CSVHF range tests of
antennas on real antennas seperate from their sometimes fanciful
claims.


I presented the theoretical calculations,
not actual measurements, sure.

Anyone with a VHF anechoic chamber?


Slick

wrote:
Hi,

Well, our Super J-pole:

http://users.marktwain.net/aschmitz/...jpolecalc.html


Is beating our Yagi in ALL directions,
even in the forward lobe!
much snippage

Must be one horridly poor yagi. Most 3 eleemnt designs are better
than 8dBi and with a little effort an be 1 db better than that.


8 dBi WITH a 180 degree pattern?
And WITH A F/B ratio that doesn't exceed 11 dB
or so?

I don't think so.

Do you have a design you can show us?



Most Stacked Jpoles do not perform as well as predicted on paper with
the upper added dipole contributing .5 to 1 db less than guessed at.


Allison


How did you come to this conclusion? What
sort of field strength equipment did you use?

Again, i would be the first to say
that reality doesn't fit the math model,
sometimes not at all. But is this case,
you can really hear the difference.



Slick
Slick

On 6 Feb 2005 14:10:37 -0800, wrote:

How did you come to this conclusion? What
sort of field strength equipment did you use?

Simple testing with a stable RF power source and a sensitive field
strength meter in a very large yard. It's not hard to determine a 1Db
difference and a 3db one is easy.

The other is a colinear design the second element cannot contribute
3db unless the first didn''t radiate any energy. Thats rarely the
case. To get the gain you claim try a 8 or more segment colinear and
note that would be about 18-20ft tall for a 2m antenna.

Again, i would be the first to say
that reality doesn't fit the math model,
sometimes not at all. But is this case,
you can really hear the difference.

Usually the math model is reality if its a real model. Often it's not.
manyy of the simple shorthand models are far for accurate or complete.
Also in some locations there are third order factors not considered.
For a real model (NEC based) the stacked Jpole is 2.3-2.4dbi better
than a plain J and ends up at about 7.4Dbi. [In real terms that's
only about 2.4 DB better than a vertical dipole which a basic Jpole
is.] That gain (7.4 DBI) is easy to beat with a 3 element beams on 2m
(typical is 8dbi) though a simpler half square is 9.4dbi. Having
built many antennas and examples of the three mentioned I find the
models are accurate. However, if you cannot measure and test the
antenna effectively you cannot evaluate if it's working as predicted
or if its working at all. At VHF execution is everything and subbing
1/4 inch tube for a modeled 1/2 inch one will give error, sometimes
significant. I'd add that at VHF the feed section is critical and if
not done well the rest of the antenna is a waste of metal. The
Jpole in this case is easier to evaluate because if the SWR is poor
it's definately not working well and a lot of things have to be
correct or the SWR will be poor.

For example, it may work better because its nearly 60inches taller and
at a given location that could be the majik. Never ignore height as a
significant factor at VHF.

If you care to read www.cebik.com/jp1.html all four sections. It's
an indepth treatize and explanation of J-poles and varients. Based
on my experience he's hit the nail accurately.

Oh, and I use two Jpoles (arrow OSJ146/440 and a Copper cactus
for 2m/440) and both match the model for performance in the real
world. Obviously I'm neither pro Jpole designs nor am I against them.
They work well to the designs limit if built carefully. I like them
for the ease of assembly of a rugged design that's reproduceable.


Allison

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