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Author Topic: Dipole antenna...bazooka?  (Read 1424 times)
KB8BAB
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Posts: 101




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« on: October 31, 2012, 06:38:08 PM »

I want to build a dipole for 80M....lots of ideas out there.... straight wire...folded...fan (for multiband)...

While searching I ran across an interesting dipole. It's made entirely out of coax and supposedly is nicely broad-banded and efficient.
Anyone has any experience with this type of antenna good/bad I'd like to hear it.

73
Bart
(now KB8BAB)

Did find this article...very interesting...
http://vk1od.net/antenna/DoubleBazooka/index.htm
« Last Edit: October 31, 2012, 07:09:27 PM by KB3HGR » Logged
WX7G
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Posts: 6038




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« Reply #1 on: October 31, 2012, 06:47:17 PM »

I built one for 80 meters and it worked well. Apparently the broadband comes from losses more than the coaxial stubs.

If you want to cover all of 80 meters a cage dipole will do it. But I prefer to use an external tuner to "broadband" a common dipole fed with coax or ladder line.
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WB2WIK
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Posts: 20595




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« Reply #2 on: October 31, 2012, 06:56:29 PM »

Double bazooka dipoles are slightly more broadbanded, but not terribly efficient.  Their loss is what makes them more broadbanded.

A large "cage" dipole is a better option, as it doesn't sacrifice efficiency for extra bandwidth -- although they're bigger and a lot heavier than a conventional dipole.
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LA3AKA
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Posts: 30




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« Reply #3 on: November 01, 2012, 02:08:16 AM »

Hi Bart

If you are looking for a good broadband 80 meter antenna, take a look at Rudy Severn's (N6LF) design here:


http://rudys.typepad.com/ant/files/antenna_broadband_dipole.pdf


73 de LA3AKA  Smiley
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W5DXP
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Posts: 3580


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« Reply #4 on: November 01, 2012, 04:34:28 AM »

Here's one way to broad-band a dipole.

http://www.w5dxp.com/notuner.com
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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.
KB8BAB
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Posts: 101




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« Reply #5 on: November 01, 2012, 05:39:14 AM »

Thanks...some great suggestions and more info to read!

73
Bart
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W8JI
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« Reply #6 on: November 01, 2012, 01:06:49 PM »

I actually measured one.

A "bazooka" has about the same bandwidth with the coax connected as a stub as it does with the coax connected just as a regular fat wire (center not used). It also has about the about the same field strength.

The bandwidth comes a little bit from outside conductor and dielectric loss (braided conductor with vinyl jacket), a little bit from being thick, and a little bit from stub loss.

If you just use a thick conductor, bandwidth gets better.

If you fan the conductors apart and use two conductors on each side, it can cover the whole band with coax feed with reasonable SWR and no extra loss.
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