"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

On Tue, 14 Oct 2008 03:04:04 GMT, "Jerry"
wrote:

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.

Hi Jerry,

Fun, maybe, but one can expend the same effort more productively and
still have as much fun.

73's
Richard Clark, KB7QHC

Thanks all for the input.

I agree, making that multielement antenna without any means for
measurements is taking a risk that it will be quite inferior to a pro
antenna and thus a waste of time. I found coaxial multielement
antennas at procomm.dk. Length is between 70 cm to 535 cm.

So I back down to a hopefully more humble project. That would be
taking a commercial mobile antenna wip of a 1/4 WL plus !/2 WL
(Smarteq.com). It has a phasing coil inbetween. There is a side mount
with a coaxial FME connector which could be used for a coaxial antenna
with a quarterwave sleeve. The protruding wing (stopper) of the side
mount would be taken off. It is then posible to slide a 1/4 WL Cu tube
over the antenna mount. By fastening the tube to mount ground, one
would obtain the sleeve needed for a coaxial exended antenna. Gain of
the whip in a ground palne confguration is 3 dB.

Should a sleeve +protruding part of mount be eaxtly a quarter
wavelength long at a velocity factor of 1 - or 0.95 ?