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darrellwood13
Antenna-Theory.com Newbie

Joined: 25 Aug 2014
Posts: 1
Location: Huntsville, AL

 Posted: Fri Sep 05, 2014 1:14 pm    Post subject: antenna element radius vs length In trying to construct a simple broadband Yagi-Uda 2 meter 3 element antenna designed at 146.52MHz I keep finding short notes on element diameter vs length, but nothing which would help me associate the two. Research indicates element diameter and length are inversely related. If so, how, or where may I find a chart, or really simple equation (calc was 40 years ago and I remember almost none of it), to help me adjust element length to properly match diameter at the aforementioned frequency? I am trying to figure out if I should use 3/4" or 1" copper or aluminum elements, as opposed to the more common 1/2". My marine band and 2 meter j-poles beach deliver, respectively, 1.2 to 1 and 1.1 to 1 SWR, so I am well pleased and having a blast learning all this stuff. Thank you for slogging through the long description. Darrell Wood The intelligence of a caveman, The enthusiasm of a child, And the funding of a Hobo.
bigSteve
Antenna Wizard

Joined: 14 Mar 2009
Posts: 265

 Posted: Sat Sep 06, 2014 7:45 pm    Post subject: Basically fat dipoles are better for your driven element in yagi antennas. There's not a huge variance though as you get the dipole fatter - basically resonance goes from 0.49 lambda (infinitely thin dipole) to like 0.45 lambda for pretty fat dipoles. So just use something pretty fat and make it like 0.46 lambda and call it good. (i.e. 46% of a wavelength at your center frequency) For the other elements in your yagi, again it isn't a huge deal. The thickness is not the critical parameter. Just get the lengths and spacing right from some table and call it good. If your VSWR is under 1.5, you won't be able to tell the difference (i.e. 1.1 vs. 1.3 doesn't matter). Hope that helps
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