Re: [amsat-bb] JavaScript Axial-Mode Helix Calculator

["Frederick M. Spinner" <fspinner@xxxxxxxxxxx>]

I'll have to try to find either a table, or some formulas for beamwidths... 
maybe next weekend?  I agree.  The ARRL book program
has a table of 1,2 and 3 dB bandwidths, but I didn't think it was
terribly useful, so I didn't take the extra hour or so to add it.

The "reflector" wavelength is simply one wavelength (29.97E+08 / freq = 1 wl 
in meters).  As far as I can tell a circle is fine-- as long
as the area of the reflector is greater than a 1 w/l circle its a
"classic Kraus helix reflector".  The 2400 MHz helix feed and
16 turn job in "Mode S: The Book" from G3RUH uses a square 125mm X 125 mm 
reflector.  I think the calculator says 124.9mm for the reflector,
so its close.  The original helix.bas program mentioned nothing about
reflectors, I though it was useful, as the calculation was done, and
already stuffed into a variable.

Enjoy..

Fred W0FMS


>From: "Jim White" <jim@coloradosatellite.com>
>To: "Frederick M. Spinner" <fspinner@hotmail.com>
>Subject: Re: [amsat-bb] JavaScript Axial-Mode Helix Calculator
>Date: Sun, 10 Dec 2000 07:00:20 -0700
>
>Fred,
>Very nice.  It would also be useful for calculating dish feeds if you
>included beam width and allowed turns down to 1.5.
>Is the info below "1 Wavelength Reflector" the diameter of a round
>reflector or something else?
>I assume the gain is dBi?
>
>Jim
>jim@coloradosatellite.com
>
>At 04:38 AM 12/10/2000 +0000, you wrote:
>>I figure I'd get off my duff, and do something useful for the
>>AO-40 community.
>>
>>A long time ago, I used to use the helix.bas program from the ARRL
>>UHF/Microwave Experimenter's Manual (vol. 1-- 1990) written by Bob Atkins,
>>KA1GT.
>>
>>Anyway, I've lost it, and because there is a relative lack of plans
>>on the internet for 1269 MHz helicies... I decided rather than typing
>>in the BASIC program again (ugh), I'd make it a JavaScript program-- and
>>hence be able to share the joy worldwide.  (Yes, it calculates in cm *and*
>>Inches for us metrically [and apparently vote counting] challenged 
>>Americans!)
>>
>>I think I have the bugs out of it.  Let me know if anyone finds
>>it useful:
>>
>>http://members.home.net/fspinner/W0FMS/Helix
>>
>>(Note: case does matter)
>>
>>Later I'll post my homebrew satellite antennas like K5OE.. but I imagine
>>it'll take quite some time before I finish and test the beasts...
>>
>>Fred W0FMS
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