Horizontal J-pole?
 

http://www.tfn.net/~gfloyd7/antenna

I'm interested in a wire gain antenna for 6m SSB, and the design above
looks like a pretty quick project. Is it possible to use a j-pole like
this above efficiently as a horizontal antenna? Couldn't it be
center-fed with, say, 2 collinear half-wave sections seperated by 1/4
phasing stubs? In doing so, I was thinking of feeding the center with
300 ohm balanced line.

Thanks for any thoughts.

-Chuck
W1CEW
www.chuckwyatt.com

A jpole is a end-fed halfwave - and because of that, lends itself well to
vertical applications.
It could just as well be oriented horizontally,
but
for a half-wave horizontal antenna,
a run-of-the-mill center fed dipole may be in order.
feed it directly with coax from the transmitter.
or not
(long runs may deserve twin lead or ladder line)

"Chuck W." wrote in message
ups.com...
http://www.tfn.net/~gfloyd7/antenna

I'm interested in a wire gain antenna for 6m SSB, and the design above
looks like a pretty quick project. Is it possible to use a j-pole like
this above efficiently as a horizontal antenna? Couldn't it be
center-fed with, say, 2 collinear half-wave sections seperated by 1/4
phasing stubs? In doing so, I was thinking of feeding the center with
300 ohm balanced line.

Thanks for any thoughts.

-Chuck
W1CEW
www.chuckwyatt.com

Won't the vertical collinear still win over the dipole because of gain,
on the order of 3-6 dbd?

Now somewhere I've seen a center-fed horizontal antenna. something like
a double Zepp, but in addition to feeding the two halfwaves on each
side, there is additional halfwave sections added to each end via 1/4
wave phasing harnesses, or maybe I'm just imagining something from an
old antenna handbook.


-Chuck

Chuck W. wrote:


Now somewhere I've seen a center-fed horizontal antenna. something like
a double Zepp, but in addition to feeding the two halfwaves on each
side, there is additional halfwave sections added to each end via 1/4
wave phasing harnesses, or maybe I'm just imagining something from an
old antenna handbook.


-Chuck



You have described a horizontal colinear antenna. It has gain broadside
to the wire but don't expect good results off of the main lobes.
Of course if you have a preferred direction, or work two locations 180
degrees apart it works nicely.

Chuck, Flame disclaimer - This is not a comprehensive tutorial on all types
of antennas or matching or all causes of loss and gain. I have simplified
things for the purpose of providing a simple to understand explanation of
this antenna which can also be used as a basis for further knowledge.
Adding all possible theoretical and practical consideration up front only
serves to confuse. With this knowledge (model in your brain) you should be
able to understand things well enough to understand this antenna and other,
related types (of which, almost all are).

To the point
Short answer:
Yes, you can feed it at the end, or for that matter, in the center of a 1/2
wave section with balanced line and a tuner/matching device.

....or at the center stub...or, wherever, with suitable matching...

(and long answer):
The "J-Pole" as most now call it, or as I prefer to call it, simply the
"J-Antenna", is been around for along time and nothing more than an end fed
half wave. I have instruction for a 20M J in my 1945 handbook. It is the
same antenna as the standard half wave "dipole", just fed on the end rather
than the center. The end is a high impedance feed point and therefore
requires something to get to/from the 50 ohm rig. The pseudo 1/4 wave
"stub" where the feedline connects is that impedance matching device. I
call it "pseudo" because I believe an exact analysis yields that it is not
precisely 1/4 wave for a perfect match, but close also counts in antennas as
well as horse shoes. End feeding probably skews the pattern a little, but a
half wave is pretty much a half wave regardless of how you feed it. You can
run it horizontally of vertically. The pattern moves accordingly, taking
the doughnut shape from the "wheel" orientation to the
"inner-tube-floating-down-the-river" orientation, respectively.
The link you give shows "two half waves in phase" also end fed. This is
called "collinear" since they share ("co") the same line ("linear"). Like
the name "coax" meaning the two conductors share ("co") the same axis
("axial").
The "...in phase" part of this is because of that 1/4 wave stub in the
center of the two 1/2 wave sections. It gets the two 1/2 wave sections in
phase by providing 180 degrees of phase shift at the ends where it connects
to the 1/2 wave sections and the stub is not supposed to be part of the
radiating system. This makes the "left" ends of each 1/2 wave the same
polarity (same story with the right ends). You can keep stacking these up
just by adding the stub and 1/2 wave section. By the way, this is a common
antenna configuration (half waves in phase) that you see mounted vertically
on the three sides of all the triangular cell towers.
Adding half waves, most certainly lowers the feed impedance, so
adjustments in the matching device/method are needed as you add them.
If you choose to feed the first one in the center, it starts as the
standard 1/2 wave dipole". If you choose the "J" matching method, it
becomes the "J-whateverYouLike" antenna. As you add 1/2 wave sections, the
pattern will become narrower along the broadside. Starting from the
"dipole" you can add them to both ends, preferably symmetrically. As the
radiation from each of these 1/2 wave sections gets out into space, they add
up in the broadside direction and cancel in others. This squirts more of
your power there and less in other directions, giving gain in that direction
(and loss in the others) -- You squish the inner tube flatter. Each time
you double the length of the whole thing (the physical length of the 1/2
wave radiating sections), you realize approximately 3 dB gain in the
broadside direction. This 3dB diminishes for each subsequent doubling, but
is an ok approximation.
Feeding antennas with open wire, or balanced line is preferred when using
an antenna on several bands, or (which is the same basic reason) where the
feed impedance is far from 50 ohms, or expected to be. This is to keep
losses low since it is expected that there will be a high VSWR on the feed
line and the matching will be done away from the antenna, most commonly, at
the transmitter.

73, Steve, K9DCI whew
haven't been reading in a while...

"Chuck W." wrote in message
ups.com...
http://www.tfn.net/~gfloyd7/antenna

I'm interested in a wire gain antenna for 6m SSB, and the design above
looks like a pretty quick project. Is it possible to use a j-pole like
this above efficiently as a horizontal antenna? Couldn't it be
center-fed with, say, 2 collinear half-wave sections seperated by 1/4
phasing stubs? In doing so, I was thinking of feeding the center with
300 ohm balanced line.

Thanks for any thoughts.

-Chuck
W1CEW
www.chuckwyatt.com

OOH!
If you want a 'gain' antenna - the easiest to do is a 5/8-wave for a
vertical, and you just add enough of a coil at the bottom to get your match
to 50 ohms. its hard to beat as far as verticals go..
and for a good gain horizontal antenna:
a double zepp - a dipole with both sides 5/8-wave - a total of 10/8 wave
( one and a quarter wave )
- but its fun to experiment with co-phased antennas -
I say - get a MFJ 259 and have fun playing.
I like quads and quagis.
but for vhf and uhf: the best improvement is height. - get that antenna up
high.


"Chuck W." wrote in message
ups.com...
Won't the vertical collinear still win over the dipole because of gain,
on the order of 3-6 dbd?

Now somewhere I've seen a center-fed horizontal antenna. something like
a double Zepp, but in addition to feeding the two halfwaves on each
side, there is additional halfwave sections added to each end via 1/4
wave phasing harnesses, or maybe I'm just imagining something from an
old antenna handbook.


-Chuck