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Re: Re: helix design question



well...kinda.
The *impedance* bandwidth can be an octave or more but the pattern bandwidth isn't that wide.  So you could get quite different edge tapers on L and S.  Actually that probably works in the amateur's favor since L is TX and S is TX/RX; and the higher-frequency end would be higher-gain/higher-taper/therefore lower sidelobes and better noise performance on the RX side of S.
Also, shorter helices--like the ones typically used to feed a dish--don't typically have the octave-bandwidth impedance properties of the multi-wavelength ("long") ones.
> 
> From: "kc6uqh" <kc6uqh@cox.net>
> Date: 2006/04/18 Tue AM 02:00:54 EDT
> To: <amsat-bb@amsat.org>,  "Robert V Johnson" <w7lrd@juno.com>
> Subject: Re: [amsat-bb] helix design question
> 
> Just a thought,
> If max gain is not a consideration and it rarely is when using it as a feed 
> for a dish most helix in the axial mode exbibit an octave of bandwith making 
> concentric helixes unnecessary for L/S mode operation.
> 
> Art,
> KC6UQH
> ----- Original Message ----- 
> From: "Robert V Johnson" <w7lrd@juno.com>
> To: <amsat-bb@amsat.org>
> Sent: Monday, April 17, 2006 12:30 AM
> Subject: [amsat-bb] helix design question
> 
> 
> > Hello
> > Bob is playing with antennas again (still).  Does anyone have any
> > experience with a dual L/S helix.  Where the S is nestled inside the L.
> > Could this be used for mode L/S or are the antennas too close.  Also what
> > would the maximum diameter of a metal center support  as a function of
> > wavelength with non metalic radial supports be?   Kraus' book is not too
> > clear with this point, his information is over kill on everything else!
> >
> > 73 Bob W7LRD
> > Seattle
> > ----
 

Scott Townley NX7U
Gilbert, AZ  DM43di
----
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