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BUILD A STURBA CURTAIN ANTENNA FOR ALL BANDS!
The
Broadside Curtain Aray
Presented by N0KHQ
(See "About feedline length" at
bottom of article)
"I live on a very small residential lot
65' wide x 100' deep. I have a tree in the front yard and a tree in the
back yard. The sterba is hung directly over the top of my house."
The
bottom element of the array is up at 35'.
The design frequency for
maximum gain was 28.5mhz.
THIS DESIGN IS FOR ALL BAND USE.... 160 THRU
10 using a Tuner!.
The standard formulas
below were used
468/freqmhz = 1/2 wavelength
section
234/freqmhz = 1/4 wavelength section.
My antenna elmer is W1VDE, Roger, He was part of the team that
built the dishes at Arecibo, Puerto Rico years ago.
I am attaching the
other half of my antenna system ( John is refering to
the Tunable Radial System in pic below for your review and
comments.) This system adds approx. 3db to 6db of additional gain to the
Sterba.
If you need further information please do not hesitate to
call.
Hams that have installed the curtain have liked it so much they
have put up more than one."
73
John / N0KHQ / St. Louis
Always
on 17M
"Antennas: You can build 'um better than you can buy
'um."
RADIAL SYSTEM
INFO
The Sterba
Curtain, as designed is non resonant.There are a couple of bands where the
swr will drop to 3:1.
The installation of the tunable buried radial
system will help on 160m, 80/75m and 40m.
If I were you I would put out
radials for those bands only.
4 for 160m
4 for 80/75m
4 for
40m
Remember, the radials should be cut at .15 of a wave not .25.
There is a 10% shortening factor when radials are either on the ground or
buried just below the grass level. By installing the radial system you
will add 3db to 6db of gain to the gain on the curtain now. (ref. ON4UN -
Low Band DXing)
I bought a HedgeHog from Lowes to dig the trenches
$50 and used, what I call chain link fence wire ties, the aluminum wire
ties are already bent in the shape of a "U" and hold the wire down very
nicely.
You wont need to run an amplifier with the antenna for good
performance.
THE
TECHNICAL STUFF GET OUT THAT CALCULATOR!
SEE EZNEC MODELS HERE
BEWARE!
LOTS OF
GRAPHICS!
This taken from recent email
from John, N0KHQ
Hi Don,
Okay, here we go. Here's an example for 17
meters.
The Sterba is approx. 50' long x 16' high.
Example Gain on 17m:
17m squared / 12.56 (4pi) =
23 sq. meters of aperture
50' / 3.28 (1 meter) = 15.24 meters
16' / 3.28 (1 meter) = 4.878 meters
15.24m x 4. 878m = 74.34
sq.meters
74.34 / 23.00 = 3.24 log x 10 = 5.09 db + 1.64 (gain
over dipole) = 6.73 db gain on 17m.
If you are running 150w x 6.73
= 1009.5 watts of effective radiated power output on 17m.
On 10m (
the design frequency) the gain is 10db +/-
The above formula can be
used for calculating aprox gain on other bands
I need to clear up
something that I may not have explained very well. This design allows a
ham to use this array on all bands 10m through 160m, on 160m the swr
bandwidth is pretty narrow.. There is no need to build arrays for
different bands.
I have not tested other Sterba's designed for other
bands as to their performance from 10m through 160m.
ABOUT FEEDLINE
LENGTH
The reason the 450 ohm feed
line is 130' is because it is about 1/4 wave length on 160m which is a
high current point. So, what ever is tied to the end of the feed
line.........is going to get out!.
For the feed line length (130') I
have tried different lengths but 130' seems to be the minimum optimum
length to get on 160 m.
Example:
I used
935/1.931=484.2' / 4 = 121.0' . This is a 1/4 wavelength at 1.931mhz, in
the example. Some have said that 450 ohm ladder wire is actually 400 ohm.
Some have said the velocity factor is not .95. Man, who really
knows?
This antenna serves me well. Since I only have room for one.
A good thing to remember is the phrase "Volumetric Efficiency".
I have sent this design to a number of hams, the design has made
it all the way to Europe. If you would like to contact a friend of mine
that waS running this array his call sign is KB4CCM, Bill now SK. He
liked it so well he put up two and gave away his other antennas!
(Bill, KB4CCM {SK} WRITES THIS ABOUT THE DESIGN.........
TAKEN FROM AN EMAIL)
" As John has told you, I have taken
down all of my other wire antennas (dipole, extended double Zepp and Half
square) due to the performance and versatility of the all band Sterbas. By
the way, you may be interested in an article I wrote which is published in
the ARRL Antenna Compendium # 7 now on sale. It is
entitled 'The ODD QUAD' and details instructions on how to
build a strong and cheap (using locally available materials) two element
Quad that can be installed and rotated without a man made vertical
structure. This Quad, along with the Sterbas, may be the only antennas I
will ever need or use for the rest of my ham career."
BACK TO THE PROJECT
The buried radial system that is
used with the Sterba adds approx. 3db to 6db of gain. Once you add this
gain to the gain of the curtain, the total gain of the antenna system is
9db to 12db of gain on 17m.
A good reference book that is
available that will help hams to understand the importance of a good
buried radial system is "Low Band DXing" by ON4UN cost $30.
Hams
running the low bands are experts on antenna systems.
I call it my
antenna bible. Hope all this helps........my head hurts!!!!!!! 73
John
/ N0KHQ / St. Louis Always on 17M
"Antennas: You can build 'um
better than you can buy 'um." N0KHQ
Editor's
note:
Many thanks to John, N0KHQ for sharing this information
for all Hams to enjoy!
and to Bill, KB4CCM. If you have questions about
this project please contact John, N0KHQ via email at:
John, N0KHQ
Email
me here!
NEW!
See John's 17 Meter Coaxial Moxon.
40 % reduction in size over standard
Moxon!
Click
here
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