> While I have not done it, I believe it may be possible to design a
> network of stubs and transformers which 'switches' automatically as
> one moves from the low to the high end of the band. I do not think the
> stub tuning will always be applicable to tuned antenna arrays, but it
> should be universally applicable to single element verticals and to
> dipoles. (I could be wrong).
The ARRL Antenna Handbook describes stub systems that work,
but they correctly point out that all stub systems add loss and it
takes a complicated system to significantly extend bandwidth
without using a switched reactance.
Why so much work anyway? First of all, a Marconi is already
around twice the bandwidth of a dipole the same thickness
because the resonant part of the antenna is half the length and the
system has "infinite bandwidth" in the half made up by a large
conventional groundplane.
Secondly, just make the antenna thick....especially at the open
ends where the electric field boundary region is. Anything you do to
reduce the voltage gradient or field density at the open ends will
increase bandwidth.
What I have always done is just made bowtie elements. A wire
cage or skeleton using a few small diameter wires is electrically
just as good as a solid conductor, and very easy to build.
73, Tom W8JI
W8JI@contesting.com
List Sponsored by AN Wireless: AN Wireless handles Rohn tower systems,
Trylon Titan towers, coax, hardline and more. Also check out our self
supporting towers up to 100 feet for under $1500!! http://www.anwireless.com
-----
FAQ on WWW: http://www.contesting.com/FAQ/towertalk
Submissions: towertalk@contesting.com
Administrative requests: towertalk-REQUEST@contesting.com
Problems: owner-towertalk@contesting.com
|