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Re: S Band Helix



Another good material is Delrin, which is lower loss than fiberglas and
higher loss than PTFE but is machinable and fairly strong. Plastics supply
houses carry this in many shapes and it is available in small quantities
from Small Parts, Inc. I used this in a three helix array for AO-40 with 3
Delrin rods supporting each helix and an acrylic end plate to maintain rod
spacing.

73,

John
KD6OZH

----- Original Message -----
From: "John B. Stephensen" <kd6ozh@verizon.net>
To: "Robert V Johnson" <w7lrd@juno.com>; <amsat-bb@amsat.org>
Sent: Thursday, June 16, 2005 17:06 UTC
Subject: Re: [amsat-bb] S Band Helix


> Using a form for a helix has two effects. It shifts the resonant frequency
> down and it increases losses. The shift can be compensated for by
decreasing
> the helix diameter. The loss increases with frequency but some materials
are
> better than others. I've used fiberglass pipe as a form at 2.4 GHz and it
> had lower losses than PVC and greater mechanical strength. For a short
> helix, PTFE (Teflon) tube might work and would have very low loss. Losses
> can also be reduced by reducing the area of the material inside the helix
by
> using thin wall pipe.
>
> Another approach is to use 3 small rods with a non-conductive support at
the
> open end. This can reduce frequency shift and losses and still support the
> helix.
>
> 73,
>
> John
> KD6OZH
>
> ----- Original Message -----
> From: "Robert V Johnson" <w7lrd@juno.com>
> To: <amsat-bb@amsat.org>
> Sent: Thursday, June 16, 2005 02:06 UTC
> Subject: [amsat-bb] S Band Helix
>
>
> > Hello
> > I'm doing some "stuff" with 2.4 ghz helix'.  I have seen some designs
> > that use a plastic type pipe  (pvc) for a form.  I bought a 1.2 ghz
> > helix on ebay that is a commercial unit and is enclosed in a large pvc
> > type pipe.  Do these forms have a significant impact on the performance
> > of these antennas?  I have read conflicting information about this.  I
> > want to establish a general consensus of what is "right".
> >
> > 73 Bob W7LRD
> > Seattle
> > ----
> > Sent via amsat-bb@amsat.org. Opinions expressed are those of the author.
> > Not an AMSAT member? Join now to support the amateur satellite program!
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> ----
> Sent via amsat-bb@amsat.org. Opinions expressed are those of the author.
> Not an AMSAT member? Join now to support the amateur satellite program!
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----
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