I want build a 8jk antenna, but i don't find a good project on
internet.
Can anyone help me?

wildboy wrote:
I want build a 8jk antenna, but i don't find a good project on
internet.
Can anyone help me?
The ARRL Antenna Book has details in CH. 8 on multi element driven
arrays. I don't know if there is a project available on the internet.
I have never built a W8JK array, although they should not be that
difficult.
Why do you want to build an 8jk, and for what band? Does it fit your
particular application, or do you just want to experiment? Just
curious.
Gary N4AST

"wildboy" wrote in news:1136934974.430378.213490
@g14g2000cwa.googlegroups.com:

I want build a 8jk antenna, but i don't find a good project on
internet.
Can anyone help me?

http://www.hard-core-dx.com/nordicdx...wire/w8jk.html



--
Dave Oldridge+
ICQ 1800667
VA7CZ

i want build this antenna because seams to be the best choise for a
multiband array with gain and no loss(less than other) for field day
use.

If i buld it for 20mt it should work also on 15-10mt without traps.And
in this way i can use fisshing pole to build it.


http://www.hard-core-dx.com/nordicdx...wire/w8jk.html
The project find on this page seams to be perfect, i do not understand
the lenght are for half element or the full element

Thanks

sorry but the first question was mine. i don't know why was posted like
"wildboy" and not "ik7ytt".
so post made by "wildboy" and "ik7ytt" are made by same person.

On 10 Jan 2006 17:38:41 -0800, "ik7ytt" wrote:

i want build this antenna because seams to be the best choise for a
multiband array with gain and no loss(less than other) for field day
use.

If i buld it for 20mt it should work also on 15-10mt without traps.And
in this way i can use fisshing pole to build it.


http://www.hard-core-dx.com/nordicdx...wire/w8jk.html
The project find on this page seams to be perfect, i do not understand
the lenght are for half element or the full element

The diagram is not clear, is it.

The basic End-fire W8JK uses two half wavelength dipoles spaced an
eight of a wavelength. It has a half twist of the openwire line
between the dipoles, and it is fed at the centre of that line.

So, for 20m, each of the two dipoles will be about 10m long (end to
end), and they will be spaced about 2.5m apart.

(The diagram might lead you to think that each half of the dipole is
around 10m, but that not correct.)

Owen
--

Thanks for explain the diagram.
But now i have another doubt.
i have found on cebik home page an example of w8jk antenna.

You can seee at http://www.cebik.com/fdim/fdim9.pdf on page 6 and 7

in this project the full element is 44'(13.2m) but spacing is 22'
(6.6m)
So in this case the element is longher than 1/2wl ( i'm also reading
that the optimum is that the full element is from 1wl to 1.25wl, so
from 20m to 25m) and spacing is between 1/8 wl to 1/2wl.

What is the best choise?
If element is to short i may have very low impedence

On 10 Jan 2006 18:32:30 -0800, "ik7ytt" wrote:

Thanks for explain the diagram.
But now i have another doubt.
i have found on cebik home page an example of w8jk antenna.

You can seee at http://www.cebik.com/fdim/fdim9.pdf on page 6 and 7

in this project the full element is 44'(13.2m) but spacing is 22'
(6.6m)

Doesn't he say it is cut for the lowest frequency, and that is 30m or
10MHz) in Table 3?

So in this case the element is longher than 1/2wl ( i'm also reading
that the optimum is that the full element is from 1wl to 1.25wl, so
from 20m to 25m) and spacing is between 1/8 wl to 1/2wl.

What is the best choise?
If element is to short i may have very low impedence
--

Hi, all concerned:

The W8JK antenna can keep its same general broadside pattern when the
lengths and spacing vary widely. So, you can build one to fit the space
available, and you need to pay attention only to keeping the 4 lengths of
element-wire close to the same length, and to crossing the phasing line over
between element feedpoints**. It will work well over a 3-to-1 frequency
range.

Element maximum-currents and voltages can be quite high, so use the largest
practicable wire size, and good insulators.

Exact lengths or "resonance" do not seem to affect patterns. It is probably
easier to use open-wire feedline. To make the antenna easier to tune, you
can vary the feedline length between the transmitter and the antenna. Make
your feedline "tune the antenna".

Modeling it with EZNEC shows that, at lower frequencies, it can have more
radiation at lower angles than some other simple antennas at the same height
above ground, and that shifting the feedpoint away from the center of the
phasing line produces a uni-directional pattern.

I hope this helps.

73,
Dave, N3HE

** uncrossed will make it a double-lazy-H ;o)

"wildboy" wrote in message
oups.com...
I want build a 8jk antenna, but i don't find a good project on
internet.
Can anyone help me?

David J Windisch wrote:
. . .
Modeling it with EZNEC shows that, at lower frequencies, it can have more
radiation at lower angles than some other simple antennas at the same height
above ground, and that shifting the feedpoint away from the center of the
phasing line produces a uni-directional pattern.
. . .

I don't think you'll see both those effects (lower radiation angle and
unidirectional pattern) at the same time.

You'll find that the elevation pattern of small to moderate sized Yagis,
log periodic antennas, and most other horizontal arrays is essentially
the same as that of a dipole, at least at the lower elevation angles.
The reason is that most horizontal arrays have a broad free space
pattern in the vertical plane -- not that much different than a dipole,
in the forward array direction. The W8JK is unusual in that respect. Its
free space vertical pattern is noticeably narrower than most other
moderately sized horizontal arrays, so it has a narrower elevation
pattern when mounted over ground, too. The net result is a greater
concentration of radiation at lower angles.

Unfortunately, the cost of this narrower vertical pattern is a
bidirectional horizontal pattern, resulting in half the applied power
being wasted unless you happen to be talking to two oppositely-located
people at once. So for a given power input, the gain is 3 dB less than a
unidirectional antenna with the same lobe width, or the same as a
unidirectional antenna with a considerably wider lobe. The only way to
fairly compare the gains is by modeling and looking at the field
strength of the antennas at the azimuth and elevation angle of interest.
(Loss must be realistically included in the models, too.) It's entirely
possible that the advantage of concentration of radiation at lower
angles is more than offset by the lower gain due to its bidirectionality
and/or loss (see the next paragraph). Of course, you can change the feed
as Dave suggests to get a unidirectional pattern. But then your free
space elevation pattern becomes a broad cardioid, and you end up with a
dipole-like elevation pattern over ground.

Among the advantages of the W8JK are simplicity and the fact that the
pattern changes very little over very wide bandwidths. On the down side
are the bidirectionality and, particularly when spacing is close, a low
feedpoint resistance and rapid change in feedpoint impedance with
frequency. The feedpoint resistance can be low enough that wire loss
becomes a concern, and if not, matching network and perhaps even
feedline loss can become significant. You're almost certain to be
running a very high SWR on the feedline, so very low loss line is a must.

Roy Lewallen, W7EL