# Re: 2.4 Ghz Helix--stacking distance

• Subject: Re: [amsat-bb] 2.4 Ghz Helix--stacking distance
• From: "Pieter Ibelings" <elpieter@xxxxxxxxxxx>
• Date: Thu, 24 May 2001 00:12:42 -0400

```Jerry,

If you look at the article "A Mode-L Helical Antenna Array for OSCAR-13" in
the 1993 page 23-35 and older handbooks, they have 4 helical antennas
stacked. They use long helix antennas with 28.5 turns. They calculate the
gain of each antenna to be 19.2 dBic and from that number arrive at a 2.59
lambda spacing. It is understandable how lowering the number of turns will
force the antennas to move in closer.

If you know the gain of an individual helix. Can this gain be used to
calculate the effective apperture and this in turn be used to calculate the
propper spacing?

Pieter

----- Original Message -----
From: <K5OE@aol.com>
To: <w4mvb@juno.com>
Cc: <elpieter@hotmail.com>; <amsat-bb@amsat.org>
Sent: Wednesday, May 23, 2001 23:45
Subject: Re: [amsat-bb] 2.4 Ghz Helix--stacking distance

> Jess, Pieter,
>
> > I've run the numbers I found in the the UHF/Microwave Experimemter's
> >  Manual and they seem to incicate that the optimum stacking distance for
> >  two 20 turn helicies is about a foot.  Can someone tell me if that is
> >  close to the correct value?  It seems a little close to me considering
> >  the boom length is about 2 feet.
>
> Exactly what do they say?  That would be 2.5 wavelengths, double the
> "typical" stacking distance for a Yagi--typically 1.25 lambda.  If capture
> area and beamwidth are the contributing elements, then a 16 dB antenna of
any
> type has a "similar" pattern (of course the sidelobes are worse in a
helix).
> The ARRL Handbook and a QST article from 1963 both specify 1.5 WL for
> stacking 2x2--or about 7.5".  The famous AF9Y 2x2 array has spacing that
> scales to 10.5" at 2401 MHz.  My limited Xerox copies of Kraus' work do
not
> address this issue.  I hope somebody that has more authoritative
references
> chimes in and offers some input, as I already have one based on 1.5 WL in
the
> works (garage).
>
> >  Yea, I know, I should buy a dish but I'm hardheaded!
> DItto!  And I have both a 2' and a 3' dish... but I want this to work :-)
> 73,
> Jerry, K5OE
>
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