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*Subject*: Re: [amsat-bb] 2.4 Ghz Helix--stacking distance*From*: "Edward R. Cole" <al7eb@xxxxxxxxxxxxx>*Date*: Thu, 24 May 2001 06:40:51 -0800

John, etal: Except for the first expression that solves the gain question, they are the same formula that I suggested. I am also deriving from Kraus and he equates Directivity with Gain. I would think a four helix array should also use a circular aperture, but then I'm not building one of these. So there you have it folks. Good designing and building! Ed >Reply-To: "John Stephensen, KD6OZH" <kd6ozh@AMSAT.Org> >I've been using the information published by John Kraus (second edition of >"Antennas") to calculate spacing. > > helix directivity = 12 * circumference^2 * turns * turns spacing > > effective aperture = (directivity * wavelength^2) / (4 * pi) > > helix spacing = 2 * sqrt(effective aperture / pi) > >The antenna dimensions are in wavelengths. For three helices, I assumed that >the effective aperture is circular and mounted them one aperture diameter >apart. These equations reduce to: > > aperture diameter = diameter * sqrt(12 * turns * turns spacing) > >The diameter is in the same units as the spacing and the turns spacing is in >wavelengths. > >For a square array you could assume that the effective aperture of each >helix is square and get a smaller spacing: > > spacing = diameter * sqrt(3 * pi * turns * turns spacing) > >The calculated spacing works reasonably well. I haven't been able to detect >any sidelobes when listening to the AO-40 beacon. > >73, > >John >KD6OZH > > >---- >Via the amsat-bb mailing list at AMSAT.ORG courtesy of AMSAT-NA. >To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org > ---- Via the amsat-bb mailing list at AMSAT.ORG courtesy of AMSAT-NA. To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org

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