"Richard Clark" wrote in message
...
On Mon, 13 Oct 2008 15:37:18 -0700 (PDT),
wrote:
The multisection Franklin antenna for UHF has been widely published on
Hi Jonas,
The links you provide offer nothing new on the subject. They are
appealing and thorough, but I notice none of them give any verified
data as to the operation characteristics (unless they are buried as
generalities within the text).
One very telling problem is that the popular method of using coaxial
sections swapping phase ignore that there are TWO measures of velocity
factor, and only ONE is being used to construct the antenna. The
interior section will NOT have the same wavelength dimension as its
exterior.
Another telling problem is that with the last link, there is ever so
much goop being added, and coils being wrapped that this MUST shift
frequencies and shifts by an unknown amount. As none of these links
offers measured characteristics, it is equal to building model train
sections for appearance's sake.
The original Franklin antenna used wire sections. You could easier
just bend one continuous wire into the appropriate shape and be done
with it. No issues of varying velocity factor, no phasing coils, no
problems of goop or wrapping tape, and you could use the same radome.
Open a commercial unit and you will find that is how the Pro's do it.
73's
Richard Clark, KB7QHC
Hi Richard
The the antenna I designed for "ACI" was a coaxial construction I left
the "skirt stubs" without dielectric so the radiators were close to 1/2
wave long since the Vp of the coax line inside was also air dielectric.
The only good thing about the array antenna project was that the customer
was happy. Also, I did learn alot while developing the array. The one
thing I remember is that there is alot of beam squint with frequency
variation when the number of elements is high. I dont expect the array of
the 8 or 10 alternating coaxes to be controlable in either VSWR nor beam
squint. But, it might be fun to try building one and try it.
Jerry