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Author Topic: Fan Dipole  (Read 1358 times)
W1RML
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Posts: 13




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« on: April 26, 2012, 10:39:28 AM »

I want to construct a simple 20 and 10 meter fan dipole which will be fed by RG8X coax. I have purchased a 1:1 Unadilla balun.  The balun has two eye bolts through which each side of the dipole antenna is connected and lead wires which directly connect to each side of the dipole.  My question is, when building a fan dipole, can I simply insert the ends of the wire for both the 20 and 10 meter dipoles through the same eye bolts and connect them all using the same lead wire?  This will not be the neatest package, nor I imagine will it be easy to solder with my relatively low power iron, but will it work?  Any other suggestions as to how to do this?  Thanks in advance for your insights!

Rich, W1RML         
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W9GB
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Posts: 2623




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« Reply #1 on: April 26, 2012, 11:32:02 AM »

Fan dipoles, photos of build
http://www.hamuniverse.com/ae5jumultibanddipole.html

http://www.hamuniverse.com/multidipole.html

http://forums.qrz.com/showthread.php?159953-My-Homebrew-Fan-Dipole-(pics)

eHam.net article on Fan dipoles
http://www.eham.net/articles/12399
« Last Edit: April 26, 2012, 11:33:40 AM by W9GB » Logged
WB6BYU
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Posts: 13243




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« Reply #2 on: April 26, 2012, 02:57:37 PM »

The eyebolts are to take the mechanical stress.  My preferred approach is to tie the
wires to the eyebolts with enough lead length left to connect the wire ends electrically
to the wire / lug / bolts / or whatever other connection is available, even if it is
connected to the eyebolt.

Good practice is to first make the wire mechanically secure, then make the electrical
connection, usually as a separate joint.  That way you don't have to try to solder
to the eyebolt itself.  For example, I usually use insulated wire, and would tie the
wire around the eyebolt and secure it with the insulation in place, leaving perhaps
a 6" tail on the end that then makes electrical connection to the wire coming
out of the balun.
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N4JTE
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« Reply #3 on: April 26, 2012, 04:38:47 PM »

YES
bob
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W1RML
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Posts: 13




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« Reply #4 on: April 27, 2012, 08:10:05 AM »

Thanks for the responses.  The gist of my question though is whether electrically connecting the ends of the 20 and 10 meter dipoles together will throw off the resonance of the antenna for the chosen frequencies.  If we assume that each side of a 20 meter dipole cut to be resonant at 14.225 should be about 16.5 feet and each side of a 10 meter dipole should be about 8.5 feet, by running them together through the eyebolt and soldering them together with the lead wire of the balun, am I creating a "single wire" of 25 feet which would no longer be resonant at the desired frequency?  I am new to antenna building, so if the question does not make sense, please let me know.         
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K1WJ
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Posts: 455




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« Reply #5 on: April 27, 2012, 08:26:46 AM »

Soldering them together is fine - the current will go to the correct wire based on frequency.

On 20m at the radio - once transmit - current will go to the 16.5ft wires.

On 10m - it will go to the 8.5ft wires.

Good to use a insulated separator - to keep wires away from each other - close to feedpoint - where soldered.

Wires will be inverted to some degree - top wires more flattop - than set below.

With inverted wire length for freq. should be about 5% shorter - than formula = 468/freg.

Try to get apex at 33ft minimum for 20m.

Made a few fan dipoles - always come out good.

73 K1WJ David
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W4VR
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« Reply #6 on: April 27, 2012, 09:06:25 AM »

Just make sure you leave enough separation between the wires to minimize interraction.  I use about 40 degrees on my fan dipole.
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WB6BYU
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« Reply #7 on: April 27, 2012, 10:59:05 AM »

Quote from: KB1VAU
...If we assume that each side of a 20 meter dipole cut to be resonant at 14.225 should be about 16.5 feet and each side of a 10 meter dipole should be about 8.5 feet, by running them together through the eyebolt and soldering them together with the lead wire of the balun, am I creating a "single wire" of 25 feet which would no longer be resonant at the desired frequency? ...       


No, they act like two separate wires as long as they are only joined at the feedpoint.
Well, actually there will be a little interaction between them, so the resonant frequencies
might not match exactly (you almost always have to do a bit of pruning in the real world
anyway, even with a single dipole wire) but close enough.

I have often put up 4 wires in parallel on each side of the feedpoint for 80, 40 (+ 15), 20 and 10m.
It does indeed work.
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