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A SUPER - GAIN ANTENNA PROJECT FOR 40 METERS Submitted by K5AXN, JERRY BARRY, San Antonio,
Tx Taken from original
plans published 1969 in 73 Magazine by Ed Dusina,
W4NVK, Melbourne, Fl
Editors note: Some of
the text description below was taken directly from the original article
and has been edited down to save space. The entire article can be found in
an old 73 magazine dated October, 1969. The rest of the article is by
K5AXN! Many thanks to both and all those who helped with some of the
research and continued testing of this
design.
++++++++++++++++++++++++++++
This project gives
enough information to build a 40 meter Super- Gain antenna designed to
help hams compete somewhat better with the foreign broadcast stations
which practically take over the band in the evening and night time. It is
based on the theory of super gain NVIS arrays, which reject QRM from low
angles.
The final design....still under testing by many hams....is
extremely simple, uncritical and offers large gain and QRM
rejection. The propagation studies and design work was done at Dusina
Enterprises in Melbourne, Florida. The antenna is described as having
approximately 9 db forward gain and an average of 15db rejection against
low angle QRM. The antenna is useful up to about 200 miles radial distance
from the transmitter in the daytime and up to around 1,000 miles at
night.
DESCRIPTION The antenna
consists of a single dipole antenna placed very close to the ground and
above a reflecting "screen" so as to limit the radiation to 90 degrees +
or - 35 degrees approximately. It is nothing more than a simple folded
dipole made from 300 ohm TV type twin lead cut to the length of 63 feet 2
inches plus or minus 1 inch and is fed in the center with RG58 coax or
some other 50 ohm coaxial cable.
It is suspended tightly between 3
supports (non-conductive) exactly 7 feet + or - 3 inches. If metallic
supports are used, it is suggested that nylon cord, about 3 - 4 feet
on each side between ends and supports to reduce the effect of capacitance
on the ends of the antenna. On the ground directly below and parallel
to the antenna, lay three reflecting wires of a non-critical length
65 to 80 feet long. One of these is laid directly below the
dipole. The other two are spaced 6 feet from the center or dipole
portion of the arrangement and again parallel to the dipole. The
reflecting wires can be laid on top of the ground for slightly better
efficiency and secured at ground level using nails bent into a U shape or
any other method you desire. Feed with about 100 feet RG58, 50 ohm
coax.
Using the exact directions above should yield about 1.05 srw
at 7.250mhz and increasing towards band edges. Some tuning may be required
as with most any antenna projects for your favorite
frequency.
Quote.W4NVK, "Due to the extreme simplicity of this
antenna and to its significant improvement in communications of this
particular band, plus its small size, I believe that if amateurs erect
such an antenna and test it for themselves, they will be quick to see the
value of it and by this means more use can be obtained from the 40 meter
band in the daytime, since it not only greatly increases the signal
strength of the stations communicating, but significantly reduces the QRM
leaving the state and rejects any QRM coming in from outside the
state."
THE USE OF THE REFLECTING SCREEN IS
VERY IMPORTANT FOR THREE REASONS!
1. ANTENNA IMPEDANCE WILL
BE 50 OHMS only when elements are cut as described with reflecting
elements installed. 2. LESS THAN 50 PERCENT EFFICIENCY without
reflectors. 3. VERY UNPREDICTABLE PATTERNS, GAIN, REJECTION AND OTHER
FACTORS due to variations of ground conductivity at each amateur's
location. The performance of
this antenna depends entirely on the
reflectors!
++++++++++++++++++++ NOW LET'S BUILD A 40 METER SUPER - GAIN
ANTENNA BY K5AXN "I used Pvc at the ends and center of the
antenna to keep it exactly 7 feet 0 inches. Our tests show 10db gain.
W8SYD, had a 10db gain over a G5RV at 50 feet up, (a 160 meter
G5RV).
The stations I work are about 200 to 300 miles out. It
is really COOL! I can copy and talk to stations I do
not even hear on my G5RV or the 14AVQ vertical antenna. This
antenna really knocks out the foreign broadcasts when the skip is long. It
was in the Oct, 1969 73 magazine. My friend, Don, K5ACX, told me about
it.
DO NOT CHANGE SPACING.....MUST BE 7 FEET + or - 3 INCHES.
DO NOT TRY TO ADD A
DIRECTOR!
YOU WILL LOSE
RANGE.....10db IS A LOT ON 40 METERS!
I have a metal roof 12 feet
away and power lines parallel about 30 feet away so you may need more
length than I did. Check SWR and tune for your frequency. You can scale
this antenna for 160 meters or 75/80 meters but NVIS will not work above
40 meters.
Editors note from
N4UJW "I talked to Jerry, K5AXN while he was using his NVIS
antenna with reflectors on 40 meters. I was using only about 10 watts ssb
(8 to 10) into a temporary inverted vee only up about 16 feet to the apex.
(I guess you could call my "antenna" a field day special and nothing to be
proud of!). Jerry was 5 9 plus about 10db into my Alinco DX 70 from
San Antonio, Tx to my QTH about 50 miles Southeast of Dallas, Tx. Great
signal! I do not recall his power output for certain, but I believe he
said about 100 watts. I did not get a signal report from him, but it was
obvious that he heard me at least Q5! He tried several different type
antennas during the QSO and the NVIS WAS THE
BEST!"
The
drawing below represents Jerry's installation. (He used a
standard dipole instead of the folded dipole in his final
installation). He used 1 inch PVC
for the supports and tied off at each end with rope to a tree and a
fence with coax laying on the ground. He used a plastic wire tie in the
center to attach the coax to the support. In his hand drawn picture sent
to me via snail mail, he shows the coax going straight down the center
support and laying on the ground. Using 29 feet 5 inches on each half
of the standard wire dipole, he is tuned for
7.266mhz. Here is the layout, of the antenna he uses below re-drawn
from his letter.

As always,
many thanks to Jerry, K5AXN, for sharing this project with the Ham
community....N4UJW Sorry! Jerry doe's not have email! Build this
project and contact him on the air! He can
probally hear you!
HI!

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