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For Dipoles, take the length and cut in in half for each half of the dipole, you SHOULD add a little extra length, and snip it off a little at a time rechecking the SWR on the antenna between snips to get it down to exactly 1:1 at your freq, remember, the if you do this at, say, 5 feet off the ground there will be some change as you raise the antenna to its final height.