Re: [amsat-bb] 2.4 Ghz Helix--stacking distance

["Edward R. Cole" <al7eb@xxxxxxxxxxxxx>]

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
>
>
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