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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