[amsat-bb] Re: 70cm Parasitic Lindy
aa2tx at comcast.net
Mon Aug 20 18:08:16 PDT 2007
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,
>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
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.
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