[TowerTalk] [Bulk] (no subject)

Grant Saviers grants2 at pacbell.net
Thu Aug 7 00:24:59 EDT 2014


If the roof is metal than ground to it and no radials are needed. If it 
is composite or concrete then a few feet should be ok and no radial or 
the antenna should be grounded to anything. (except an RF choke to 
building ground for static).  I encourage you to check out the extensive 
work on elevated radials by Rudy Severns N6LF  see antennasbyn6lf.com.  
You can probably find some compromise lengths to cover more than one 
band, otherwise use a tuned set of 4 for each band of interest, although 
2 (like a dipole) yield a symmetrical pattern in azimuth within 1 db.  
Insulated wire makes little difference, except it might last longer in 
corrosive atmospheres.

EZNEC would also be a good investment.  Drooping radials 30 degrees can 
change the pattern a bit and get the Z closer to 50 ohms, otherwise a 
50::25 ohm balun might be needed.

I'm not a fan of the 43' vertical (I had one as a GOTA when I moved).   
The pattern is too elevated on higher bands.  A good trap vertical or a 
HyTower (terrific) might be a better choice. Even better would be a 3 
band fan dipole, given the height of the roof. If you have the space, an 
80/40/20 would also work ok on 15 (40/20 would also).  Or put two up 
orthogonal to each other, two separate feed lines and good chokes at the 
feedpoint since stuff in/on the roof/building will almost certainly 
unbalance the antenna.

Again, with EZNEC (or 4nec2) you will learn a lot about what works and 
what doesn't.

Grant  KZ1W


On 8/5/2014 10:54 AM, Tony Rogozinski wrote:
>
>
>
> I want to put up a Zero-Five 43 foot vertical on the roof of the apartment
> building where I live here in Colombia.  I'm on the top floor - only 6
> floors - and will obviously use elevated radials.  The question is:
>
> Would it be better to mount the antenna say 3 or 4 feet above the highest
> part of the building ie the stairwell to the roof or use a pipe and raise
> it to perhaps 20 feet above that level?
>
> Raising it of course would put the antenna and radials much higher above the
> building structure and all the rebar/other metal in the structure and in
> my mind would be the best alternative.........but????
>
> It has also been suggested to use insulated wire for the radials - why?
>
> Thanks for any comments.
>
>
>                 Tony  W4OI/HK1AR
>              Licenses Previously Held:
>      N7BG, K5LMJ, W7HZF,  WA6BOU, W6JPC, K4KES
>       F7BK, VQ9AR, VP5AR, 9G5AR, TY5AR, CN2BG
>         HK0/HK1AR, 5V7BG, TU/N7BG, OJ0/N7BG
>         5B4/N7BG, ZC4/N7BG, ZF2AR, HB9/N7BG
>                     and others
>       Founding Member of VooDude Contest Group
>           Member of Florida Contest Group
>        Member Central Arizona DX Association
>            Referee WRTC 2000, 2002, 2006
>           I've been to 103 DXCC Countries
>
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