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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 |
#2
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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 |
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Design measurements for a multielement vertical NMT-CDMA450 antenna
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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 |
#6
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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 ? |
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