In article %4WRg.9158$Wi1.6469@trnddc06,
Jerry Martes wrote:

Hi,

I created a "omni-directional" vertical antenna that NEC-2 reports to
have a free-space gain 4 dBi. The shape of the antenna looks like:


------+
A |
| B
|
+-----+
C * (* = feed point)
+-----+
|
|
|
------+

The lengths can be adjusted to give the antenna a 50 ohm feedpoint
impedence. The overall length of wire forming the antenna (4A+2B+C)
is on the order of 1.5\lambda and the height (2B) is something like
\lambda. I built this antenna for 2-meters and it seems to perform
quite well. The .nec files and parameters are available from my
antenna pages at http://www.jedsoft.org/fun/antennas/omni.html.

I am sure that I am not the first to create this simple antenna,
nevertheless a google search has turned up nothing similar. Have you
seen such an antenna before and if so, what is it called? I suspect
that it belongs to some class of antennas (antennae?). I would
like to give the proper credit and name for it on my web page.

I really got interested in the configuration you show for the antenna.
But, when I looked more closely to the Elevation Plane Pattern that looks so
narrow (high gain), I realized that the antenna is very much the same
pattern as a basic full wave center fed wire.
The graduations on the plot graph was misleading to me.
Perhaps there is something special about this antenna that I am missing.

I believe that this antenna can probably be placed in the general
class of center-fed collinears. Other antennas in this class include
the center-fed fullwave, the classic Franklin antenna, and the EDZ
(extended double Zepp). The "Super-J" is a somewhat-similar design,
but is end-fed rather than center-fed.

The center-fed collinears of this sort tend to have a high (and/or
rather reactive) feedpoint impedance. They're usually fed through a
section of transmission line - often shorted at the end and fed via a
tap partway up the section... the "universal stub".

Based on the dimensions you posted, it looks to me as if this antenna
is pretty close to being an EDZ, but with the ends of the radiators
bent back sideways. I'd guess that by bending the ends sideways, and
fiddling with their lengths (and that of the matching section) you've
been able to match the 50-ohm feedline impedance without needing a
shorted/tapped matching section.

The elevation pattern of the antenna shows a hint of the high-angle
secondary lobes which characterize an EDZ.

So, I'd conclude that you've developed a variant on the EDZ (or
something partway between an EDZ and a center-fed fullwave) which
yields slightly lower gain than an EDZ but has a simpler matching
section.

The one thing I'd watch out for, with this design, is the folded-back
ends of the radiating arms. This design puts these high-voltage,
high-impedance points right at the mast, and this might make this
antenna more subject to mast/antenna coupling and de-tuning than a
traditional EDZ or full-wave center-fed.

The old ARRL VHF handbook has quite a bit of information on these
sorts of collinears, and has a nice writeup on the "universal stub"
matching technique (not very well known these days, but quite useful).

--
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!