Design measurements for a multielement vertical NMT-CDMA450 antenna
 

The multisection Franklin antenna for UHF has been widely published on
the web. The first design is by N9ZIA:

http://www.qsl.net/n9zia/wireless/col432/index.html

This antenna used ground plane radials for decoupling

A modification by N1HFX uses a sleeve and ferrite toroids for
decoupling:

www.rason.org/Projects/collant/collant.htm

There is also a design proposed by WA6SVT with a few variations in
which a tubular sleeve is used and the coax elements covered with
cupper tubes:

http://www.repeater-builder.com/ante...struction.html

I would like to build a pair of vertical multielement antennas for
mobile use (when standing still) use to be used in cdma450 cell fringe
zones. 7-9 dB gain should be enough to reach base stations of the
outskirts of cells.

I suppose that a combination of the principles outlined in the
articles by N1HFX and the ones cited around the WA6SVT design should
work. Any feedback would be appreciated.

Q: How come coils are not used to space half-wave elements from each
other? In several wifi designs, single loop coils are used. In some,
coils consist of several turns:

http://mobileaccess.de/wlan/download...0-all-inst.pdf

So, what size should a phasing coil be for 455 MHz?

Regards
Jonas/SM0WJY

Design measurements for a multielement vertical NMT-CDMA450 antenna
 

wrote in message
...
The multisection Franklin antenna for UHF has been widely published on
the web. The first design is by N9ZIA:

http://www.qsl.net/n9zia/wireless/col432/index.html

This antenna used ground plane radials for decoupling

A modification by N1HFX uses a sleeve and ferrite toroids for
decoupling:

www.rason.org/Projects/collant/collant.htm

There is also a design proposed by WA6SVT with a few variations in
which a tubular sleeve is used and the coax elements covered with
cupper tubes:

http://www.repeater-builder.com/ante...struction.html

I would like to build a pair of vertical multielement antennas for
mobile use (when standing still) use to be used in cdma450 cell fringe
zones. 7-9 dB gain should be enough to reach base stations of the
outskirts of cells.

I suppose that a combination of the principles outlined in the
articles by N1HFX and the ones cited around the WA6SVT design should
work. Any feedback would be appreciated.

Q: How come coils are not used to space half-wave elements from each
other? In several wifi designs, single loop coils are used. In some,
coils consist of several turns:

http://mobileaccess.de/wlan/download...0-all-inst.pdf

So, what size should a phasing coil be for 455 MHz?

Regards
Jonas/SM0WJY


Hi Jonas

It isnt made clear that this colinear array of 1/ wave diplies is quite
sensitive to ferquency change and intolerant to construction errors. If
you ask questions like "what size should the phasing coils be", you find
some difficulty in getting a long array to work. I'd advise you to try one
of the designs that doesnt use "phasing coils" and just try whatever is easy
for you to build.
I have (in the 1960s) designed and manufactured antennas using this end
fed concept. The radiation pattern is effected by frequency change. The
beam max will squint up with higher ferquencies and downward with lower
frequencies.

Jerry KD6JDJ

Design measurements for a multielement vertical NMT-CDMA450 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

Design measurements for a multielement vertical NMT-CDMA450 antenna
 

"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

Design measurements for a multielement vertical NMT-CDMA450 antenna
 

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

Design measurements for a multielement vertical NMT-CDMA450antenna
 

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 ?