Re: [amsat-bb] helix design question

[Charles Suckling <charlie@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx>]

Bob

Please take a look also at http://www.g3wdg.free-online.co.uk/dual.htm

I used this feed on 1.5m and  3m dishes with great success on AO40 for L/S 
operation. It worked with no noticeable degradation of either helix by the 
other (compared performance of each on its own withour the other present).

The only thing you need to take care of is the coupling between them which 
would likely desense  S-Band RX while tx on L-Band.  I used a low loss 
notch filter with 100dB rejection of L-Band on the front of the S 
downconverter and this took care of this completely.

73

Charlie


At 09:34 17/04/2006, you wrote:
>----- Original Message -----
>From: "Robert V Johnson" <>
>To: <>
>Sent: Monday, April 17, 2006 9:30 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
>
>Hi Bob W7LRD
>
>Look at the following site to see a picture of  a dual mode L/S helix feed
>
>http://www.ultimatecharger.com/Dish_Feed.html
>
>73" de
>
>i8CVS Domenico
>----
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