RadioBanter - View Single Post - Design measurements for a multielement vertical NMT-CDMA450 antenna

Richard Clark · October 14th 08, 12:50 AM posted to rec.radio.amateur.antenna

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