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Re: Seeking info on stacked helices



Hi all,
Yes I know - I should write after the other text -

but I would very much like to know if anyone have
actually built the 4 helix construction from the
ARRL Antenna Book on 2.4 GHz with a good documented
result.

I have made measurements and adjusted a 23 cm array
with 4 helix antennas as described in the Antenna Book -
but attempts on 2.4 GHz turned out very badly.

73 de OZ1MY/Ib


----- Original Message -----
From: "Edward R. Cole" <al7eb@ptialaska.net>
To: <amsat-bb@AMSAT.Org>
Sent: Thursday, July 12, 2001 4:06 AM
Subject: Re: [amsat-bb] Seeking info on stacked helices


> >From: "Bill Magnusson" <williamb@netc.net.au>
> >>I would like to talk to those who have stacked helices for 2.4GHz.  I
have
> >>one 20T helix and I want to improve things. How difficult is it?
> >>How is it done?  Is there much to be gained, besides 3DB?
> >
> >Hi Allen,
> >
> >There was a  good article in one of the ARRL publications ... the Antenna
> Handbook, I
> >think. It described a method of stacking 4 helix antennas against a
common
> screen
> >reflector and used tapered lines running in to a central "N" connector to
> achieve the feed
> >and matching section. Very simple looking and easy to duplicate. I don't
> have the article
> >here but I'm sure someone will give you a detailed reference. On 2.4 GHz
> you could hold it
> >one hand ... a definite possibility for S-band. I built one several years
> ago for 70cm and
> >it worked well on ao-10.
> >
> >Bill ... vk3jt
> >Milawa
> >Australia
>
> Bill and Allen,
>
> That design is right from John Kraus' textbook "Antennas".  Dr Kraus
> decribes his development of the helix antenna in chapter-13 of his book
> "Big Ear".  In chapter-14 there is a picture of his 96 helix array.
>
> Four will give more of a measurable improvement over one helix {6 dB
> theoretical...~5 dB actual due to losses}.  But John Stephensen is correct
> that a dish will give you a cleaner pattern and is much simpler to build
> for more gain.  {When I upgraded from an 18-inch diameter dish to a
33-inch
> dish I improved my gain about 6 dB}
>
> The tapered lines work as micro-strip transmission lines.  They taper away
> from the common reflector plate to connect at a central connector.
> Probably use 1/4 inch wide brass strips spaced about 1/8 inch at the helix
> and 3/16 inch at the connector.  That should transform your 140/4 ohm
> impedance to 50 ohms.  If you can make the helixes movable you could vary
> the spacing to obtain a best match.
>
> But even with four 20-turn helical antennas your gain will be low for good
> receiving of AO-40.  I would guess a single 18 inch dish would equal them
> [~19 dBi gain].
>
> Ed
>
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>

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