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Author Topic: Wire beam for 20m band  (Read 3302 times)
9A5BDP
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Posts: 117




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« on: February 10, 2013, 02:22:32 PM »

Hi there..
I am looking for a information how to properly build wire beam with gain for 20m band. Do any of you have some ideas?

My ideas regarding this antenna are mixed one:

- hb9cv with extra directors
- telerana lpda
- w8jk with directors (if this is possible)
- clasic multielement yagi

What of these will be better to use?
I will put antenna in fixed azimuth position.

73!
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WA2TPU
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Posts: 224




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« Reply #1 on: February 10, 2013, 03:24:49 PM »

To 9A5BDP......
    Hello. I'm WA2TPU- a fairly serious Qrper who loves to build antennas. You might want to submit to this forum what your area in the or meters is going to be. In other words....how big of an open space might you have plus the height above ground where you're going to install this wire antenna.
For me here....I build and use vertically polarized wire log periodics strung on ropes between my trees. I also make and use fixed directions Delta loop antennas- again, strung on ropes between my trees. Over the many years of building wire antennas I've also made mono-bander vertical arrays, Vee Beams and even a Rhombic and Sterba Curtain. My favorite wire antenna is the log periodic which can be made into a mono-band Log Yagi combination. This Log Yagi(to me) combines the best of both of what the Log and Yagi has to offer. The Log Yagi combo uses a 3 or 4 element Log periodic cell for the driver of this combo....In doing this the SWR stays relatively flat throughout the whole 20 meter band, Behind this 20 meter Log cell you put a Yagi type reflector at .12 Wavelength spacing.....out in front of the Log cell driver you can install a number of 20 meter Yagi directors at various wavelengths given what the space is to you have to use. With the Yagi type directors and the Yagi type reflector you get fairly decent front to back...plus with those Yagi directors the forward gain adds up quite nicely.
I gave you this 20 meter mono-bander Log Yagi combo as a decent example what can be done with wire , rope and trees. There are many more FINE wire antennas with some good gain that can be built by you too.
And I'm rambling.
Good luck with your antenna building projects. I tip my hat to you for wanting to build instead of wanting to buy.
Best regards and many 72/73.
Don sr. --WA2TPU -- A TRUE 5 WATT QRP GREEN STATION.
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NH7O
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Posts: 126


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« Reply #2 on: February 10, 2013, 05:15:28 PM »

The answer will depend to some extent on how the antenna is supported.

On tower with spreaders? Trees and ropes? Do you want to make it reversible by use of relays?
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WB6BYU
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Posts: 13567




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« Reply #3 on: February 10, 2013, 08:32:59 PM »

How high are your supports?  What distance do you want to cover?
How narrow of a beamwidth is acceptable?

How much distance to you have available in both length and width pointing in
the desired direction?


There are many different options:

A Sterba Curtain would go broadside to the desired direction.  It is bidirectional
unless you add a reflector curtain behind it.  You can build them for any width,
though the beamwidth is rather narrow at 3 wavelengths wide.

A Rhombic is fairly simple and gives some gain even without precise measurements,
but the gain is not as high as you can get from other methods for the same land
area or wire length.  With 2.5 wavelengths of wire on each leg the antenna itself
would be about 4 wavelengths long and 3 wavelengths wide.

The simplest approach that I've found is to run a single rope in the desired
direction and hang wire inverted vee elements over it to make a wire yagi.
This can be any length up to the maximum available with proper design.
With the OWA designs you can get good bandwidth and direct 50 ohm feed. 
This is much simpler than any of the other designs you listed.  (You can use
the same construction method to make a long LPDA array, which requires
phasing wires to connect the elements.)

The other approach is a quad or delta loop, also hanging from a single rope
pointing in the desired direction.  If you are limited to low heights then I'd
use two ropes at the top and string the flat part of the delta between them
with the point down, though it usually is more convenient to put the point up
and hang it from a single rope.  Again you can make such antennas of any
desired length.  A  yagi will probably have a slight gain advantage over a quad
of the same boom length once you get past about 4 elements, but the quad
may be easier to install in some situations.

If you want more gain, make the quad elements in the form of a Bisquare
instead of a full wave loop, assuming you have enough height above ground
available so the bottom isn't too close to the ground.

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9A5BDP
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Posts: 117




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« Reply #4 on: February 11, 2013, 01:06:48 AM »

Hi there..
My possible antenna ground have following dimensions 65ft x 140ft. On first third of length I have some power lines on 33ft above ground so this is maximum high on that part, on other sides high is no problem. On middle of estate one tree is planted with usefull branches up to 33ft.
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W5DXP
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« Reply #5 on: February 11, 2013, 05:47:33 AM »

Here's an interesting fixed 20m wire beam that I have always wanted to try. The driven element is 88 ft. long, i.e. an EDZ on 20m. 12 feet away from the driven element are two collinear reflectors, each 34 feet long. The antenna is 40 ft. off the ground. It is fed with a tuned feeder of 10.6 ft. of 450 ohm ladder-line with a 238pF shunt capacitor (at the choke end) to a 1:1 choke and coax (SWR=1:1) the rest of the way to the shack. It has 14 dBi gain with a take-off-angle of 23 degrees.

http://www.w5dxp.com/20EDZBEM.JPG

Or feed it with 10'+N(31.2') of VF=0.9 Ladder-Line (without the shunt capacitor) and use it for 40m-10m operation.

« Last Edit: February 11, 2013, 06:09:45 AM by W5DXP » Logged
9A5BDP
Member

Posts: 117




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« Reply #6 on: February 11, 2013, 10:40:59 AM »

This antenna looks interesant but I need some sort of proved design, also my future antenna must have beam direction in point of smaller side of estate. Total length of radiator wire must be below of 65ft dimension. In this case is antenna beaming for north America.
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N4JTE
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Posts: 1159




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« Reply #7 on: February 11, 2013, 04:22:09 PM »

I use a 20 meter phased pair of dipoles with good gain and front to back, reversable.
Both are equal length at 34 ft and seperated by 16 ft, 1/4 wl, with correct phase lines, a great beam antenna with wide beamwidth and bandwidth.
Mine is at 40 ft supported by trees and competes very nicely with tower beams.
40 version on my qrz page.
Bob
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WB6BYU
Member

Posts: 13567




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« Reply #8 on: February 12, 2013, 08:06:35 AM »

Added height may make more difference than total antenna gain.

I have an 8-element yagi model based on a DK7YB design that is 45m long
and about 10m wide, that might be a good starting point.  We may need
to cut it down to 5 or 6 elements to make it more practical in your space.
The easiest way to install it would be a inverted vee elements over a
support rope stretched between two supports.

I also have a design for a 5-element delta loop beam that is 18.5m long,
but if you are restricted to 10m height, then the yagi is a better choice
because it will have a lower angle of radiation.

To get an idea of the impact of height I compared the yagi at 10m and
at 15m above ground:  at an elevation angle of 10 degrees, the 8-element
yagi at 10m gave the same performance as a 5-element yagi 21m long
at 15m off the ground.  So at 15m high it requires less than half the
antenna length to get the same radiated power.
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