wrote:

What lack of decoupling? It's got the
coax inductive choke on the input, 4 turns
of 4" diameter.

I don't recall seeing that in the picture. But even still, I
wonder if it's as good as a full 1/4 wave decoupling cone, or
radials...Much better than nothing though...


Take another look...




Yea, but if you are going to post a CAPS thread
claiming a j pole beats a yagi by 1 db, most are
going to assume the yagi isn't crippled up...
It's sort of Frackish.....:/

How broad or narrow is the front lobe
of your yagi? How many degrees? Much
smaller than 180 no doubt.

No doubt...

I'm not trying to rain on your parade, and surely
applaud you for building these, I just don't quite
get the purpose of such a comparison...Everyone
already knows what the gains of the antennas are..
Well, except for the de-tuned yagi... I mean,
is it really a surprise a collinear might beat
a yagi with about half the normal gain of the
NBS 3 el?
I'll bow out...I really have no problem with the
antenna, etc...I just wanted to stir it, being you
have this frackish thread title... MK


Oh, ok, so you thought i was making some
sort of grand statement that a Super J will
beat a Yagi regardless of the design. That's
not what i'm saying at all.

With THIS PARTICULAR 180 degree yagi,
the Super J beats it in all directions.
Really i should have just made the thread
title, "Observations on the Super J-pole
and Wide angle Yagis in the VHF broadcast
band".

If someone can come up with a 3 element
yagi (we wanted to keep the size down), with
a 180 degree front lobe, and about 11 dB F/B
ratio, that has a better than 4.5 dBi in the
front lobe, i'd like to see it. Use EZNEC
or whatever simulator you have, and make
an H-plane plot... i'd like to see that.

The reason we wanted 11dB F/B ratio,
is that for this particular usage, it
was NOT on the edge of town, and so we
still wanted to have enough ERP to the
back side.


Slick

wrote:
You are lucky to see the gain you have, considering the lack
of decoupling...Or at least in that pix....Also, thats a
pretty lame yagi, so like you say, not really a fair test...


What lack of decoupling? It's got the
coax inductive choke on the input, 4 turns
of 4" diameter.

If you would read my posts more carefully,
you would be aware that the reason for the low
dBi is that the lobe is 180 degrees, and F/B
ratio limited to around 11dB.


My 3 el vertical yagi would eat that j pole for lunch, being
it has about 9.4 dbi gain...Or about 7.3 dbd....


So what, the Super J-pole in omnidirectional,
so that's not saying much for a Yagi. We could have
easily designed it with more gain, but the frontal
lobe would have been way narrower.

How broad or narrow is the front lobe
of your yagi? How many degrees? Much
smaller than 180 no doubt.



Slick

Dr. Slick wrote;
"Well, our super J-pole is bearing our yagi in ALL directions, even in
the forward lobe."

It`s possible.

This thread pits a "Super J-Pole" with 6 dBd gain against a "Yagi-Uda"
with 2.85 to 17.85 dBd gain (5 to 20 dBi), depending on construction.
So, it could be true for some 2-element Yagi or it could untrue for a
Yagi with 3 or more elements. A 3-element Yagi may give about 5 or 6 dBd
gain.

The "ARRL Antenna Book" gives the details. In my 19th edition, the Super
J-Pole is asid to give 6 dB gain over a 1/4-wave whip on page 16-27.

The whip with a perfect reflection (a ground-plane antenna) is said on
page 13-10 to be equivalent to a 1/2-wave dipole in free-space: "---the
image of a vertical antenna is in phase with the vertical radiator". The
whip with the perfect reflection is thus identical to a 1/2-wave in
free-space in performance. Gain of the ground-plane is 0 dBd or +2.15
dBi.

Best regards, Richard Harrison, KB5WZI

Richard Harrison wrote:
Dr. Slick wrote;
"Well, our super J-pole is bearing our yagi in ALL directions, even
in
the forward lobe."

It`s possible.


it's true. But this doesn't mean that
it's going to beat ALL Yagis, which
is what some people have thought this
thread was all about. Just THIS 180
degree Yagi, with 11 dB F/B ratio.



This thread pits a "Super J-Pole" with 6 dBd gain against a
"Yagi-Uda"
with 2.85 to 17.85 dBd gain (5 to 20 dBi), depending on construction.


6 dBd would be about 8.15 dBi, which is not
the case here.

The Super J-pole is 5.5 dBi or 3.35 dBd.

This particular Yagi is about 4.5 dBi
in the front lobe, which was a compromise
to get the 180 degree pattern (and 11dB F/B).





The "ARRL Antenna Book" gives the details. In my 19th edition, the
Super
J-Pole is asid to give 6 dB gain over a 1/4-wave whip on page 16-27.


Really? If we say the 1/4 wave is 2.15 dBi, then
the Super J is 3.35dBd, omni.

So i'm not sure where they got these numbers,
or if we are talking about the same thing.


Slick