[amsat-bb] Re: 70cm Parasitic Lindy

[Anthony Monteiro <aa2tx@xxxxxxxxxxx>]

At 09:43 AM 8/20/2007, SV1BSX wrote:
>  Hi Tony,
>
>Thanks for publishing of your "Para-Lindy", definitely
>your arrangement solved all
>difficulties and puzzles from the previous complicated
>designs. Its  quite simple now and easy to make it,
>for anybody.
>My compliments for your clever design.
>
>  Just a question:
>
>  Why not the coaxial-feeder inside of down-part
>dipole's tube (as sleeve) but outside of this?
>
>  Thanks again for publishing.
>
>73 de Mak, SV1BSX

Hi Mak,

Thanks for your interest!

When I was working on this last year, I had a lot of
trouble getting consistent performance using a sleeve
BALUN (i.e. with the coax running down the center) so
I came up with the ferrites as an alternative. Just running the
coax down the center is not sufficient to decouple
the feed from the antenna. Whats more, I want the antenna
to be very easy to build using standard plumbing
parts and not require any machined parts or require
any high-precision work to get good results. This means it needs
to have a wide bandwidth.

But, I have continued working on this antenna and hope to have
a new version to present at the 2007 AMSAT-NA Space Symposium
that will in fact use a sleeve BALUN instead of the ferrites.

The trick is to use a very thin coax cable along with the plumbing
parts that dielectrically load the sleeve so that the resulting BALUN
presents a high decoupling impedance across a wide bandwidth. This
eliminates the need for tuning or high-precision work.

I am still finalizing the design but with a little luck I will
have it for the October Symposium.

73,
Tony AA2TX

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