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Author Topic: home brew 17 meter beam.or 40 meter  (Read 8379 times)
VE7REN
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Posts: 473




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« on: November 14, 2010, 07:18:06 AM »

been surfing the net and cant find any great info or details on how to build a 17 or 40 meter beam. ideally, i want a 17 meter. i have plenty of aluminum from some crashed 12 meter antennas. boom material etc,etc. does anyone have any suggestions??

my tower would sure like to have one on it
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N2CJ
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« Reply #1 on: November 14, 2010, 07:32:57 AM »

The physical dimensions of a 40M beam are probably much too large for the project you have in mind. 17M is quite doable. Just google "yagi design" and you will come of with lots of sites that discuss this. Also, you might consider a 17M Moxon antenna, even though this will not require the aluminum tubing you are planning on using.
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WB6BYU
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« Reply #2 on: November 14, 2010, 08:55:21 AM »

There are a number of designs available, and any yagi design for 20m to 10m can be rescaled to 17m with
good results (as long as you adjust for the difference in element diameters, etc.)  The mechanical aspects
of mounting the elements are no different than for the other bands, either.  So if you find a 20m or 15m
design that meets your needs for gain, F/B, and number of elements, it is an easy matter to build it for 17m.
(Remember to scale the element diameter along with the lengths.)

Here are some resources that you may find interesting and/or useful:

http://www.cebik.com/content/fdim/fdim11.pdf
http://www.cebik.com/content/a10/yagi/3lyg.html
http://www.cebik.com/content/a10/vhf/scales.html
http://www.cebik.com/content/a10/yagi/eq-yag-1.html
http://www.cebik.com/content/a10/yagi/5l20.html
http://www.ifwtech.co.uk/g3sek/diy-yagi/index.htm (scroll down to "Element and Boom Corrections")
http://www.mydarc.de/dk7zb/3-Ele-Kurzwelle/17m-28Ohm.htm
http://www.mydarc.de/dk7zb/3-Ele-Kurzwelle/4-17m-28ohm.htm
http://www.mydarc.de/dk7zb/2-Ele-Kurzwelle/2-Ele-17m-Dir28.htm
http://www.g0ksc.co.uk/
http://www.arrl.org/files/file/protected/Group/Members/Technology/tis/info/pdf/0008057.pdf

Meanwhile, W2PV developed an interesting 4-element yagi with rather narrow bandwidth and irregular
element spacing that is ideally suited for the narrower WARC bands called the "PV4".  My 1988 ARRL
Antenna Book has design information and a 12m example summarized from a 1986 article in QST.


So if you decide how many elements you want on what length of boom (based on designs for other
bands) it can be converted to 17m fairly easily.
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N7DM
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Posts: 671




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« Reply #3 on: November 14, 2010, 10:51:08 AM »

If you have the room, and if it would 'fit'.... I suggest a 17 meter Quad. Quads are **enormously** easier to 'tune' than a Yagi.... {By tune, I mean for radiation pattern, F/B.... not mere SWR}

I am currently using the D.E. of a recent 17m Quad Build. No need for the parasite here; nothing is ever alive on the backside of MY array.....

dm
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G3TXQ
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Posts: 1523




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« Reply #4 on: November 14, 2010, 11:31:29 AM »

Take a look at the Hexbeam. It is relatively easy to home-brew and a 40m version is certainly possible.

30m/40m version:  http://n6aq.com/?p=379
Other bands: http://www.leoshoemaker.com/hexbeambyk4kio/general.html

73,
Steve G3TXQ
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VE7REN
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Posts: 473




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« Reply #5 on: November 15, 2010, 05:46:43 AM »

thanks for the input. ive looked at the hex beam,although i find the "look" a bit disgusting. i found a few other alternatives for a 17 meter beam.
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WA3SKN
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Posts: 5496




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« Reply #6 on: November 15, 2010, 08:53:11 AM »

OK, you have some spare aluminum and want to homebrew a beam.  Let's keep this simple and use ballpark figures.
Use the "468/wavelength" to get the length of your driven element.
Add about 5 percent to that length to make the reflector.  Mount it .2 wavelength away from the driven element.
Subtract about 5 percent and use this length to make your director.  Mount it on the other side of the driven element, about .1 wavelength away.
The impedance at the center of the driven element will be less than 50 ohms.  Most hams use a "gamma match" to connect the coax, this will keep the driven element at "DC" potential.  This design will have to be done experimentally.
Pick boom material and hardware to stand up to the rigors of the weather, etc.  You don't want it to fall down!
Good luck with the project.
73s.

-Mike.

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W5DXP
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« Reply #7 on: November 15, 2010, 08:56:39 AM »

http://www.qsl.net/qrp/ant/xbeam.htm
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73, Cecil, www.w5dxp.com
The purpose of an antenna tuner is to increase the current through the radiation resistance at the antenna to the maximum available magnitude resulting in a radiated power of I2(RRAD) from the antenna.
G0GQK
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Posts: 634




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« Reply #8 on: November 15, 2010, 02:57:03 PM »

Perhaps you should draw to scale the 40 metre antenna you envisage and having measured it on the ground realise just how big it will be !
Your solution could be a 2 element yagi for 17 metres and a quarter wave vertical for 40 metres.

Mel G0GQK
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N4MPM
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Posts: 72




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« Reply #9 on: November 17, 2010, 12:07:13 PM »

I constructed a 17 meter two element beam that has a 5ft. 6 in. boom.  Gamma match in a driven element-director configuration.  Good results, and have used for over 10 years with no problems.
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