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-   -   accounting for outer diameter (http://forum.tvfool.com/showthread.php?t=13060)

 thom 9-Feb-2013 5:39 PM

accounting for outer diameter

Hi All,

So I understand that the outer diameter of a dipole affects its bandwidth (more diameter, more bandwidth), but it also affects the resonant length of the dipole. Is there an equation for calculating the reduction in length for increased outer diameter, or is it not that significant?

Thanks,
Thom

 GroundUrMast 9-Feb-2013 6:51 PM

It's fairly easy to find 'rule of thumb' formulas. Typical of these is this from ARRL: http://www.arrl.org/files/file/Techn...df/9106023.pdf. It simply comes down to 468 / f (MHz) = dipole length in feet.

To get much more precision, one needs to use such formula as a starting point. As the ARRL article above suggests, you need some means of measuring the actual frequency of resonance once you get close. You'll find that other elements and components near the antenna element will also affect the resonant frequency, not just it's length and diameter.

Now days, it's become common to model an antenna design in software. The number crunching is far faster, and with good software, you get to account for element interactions. 4NEC2 is available for free download, and there's a fair size group of users to draw ideas and experience from. http://home.ict.nl/~arivoors/, http://www.digitalhome.ca/forum/forumdisplay.php?f=186

 thom 9-Feb-2013 8:34 PM

4nec2

Thank you for the prompt response and links. I hadn't realized 4NEC2 was actually free. Looks like it's has enough capability to keep me busy for a long while, but will no doubt save many trips up on the roof.

Thanks,
Thom

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