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Vertical Help
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by m5ric on January 3, 2002
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Hello
I Would like to know what a good height is for mounting a multiband vertical(HF6V etc) for best results.
Lots of people have verticals ground mounted that work fine with good results, if I were to mount a vertical above the ground and not on a roof what would be a suggested minimum height be, or is it a case of the higher the better?
Also if I were to mount it at 20ft above the ground what would the best way to get the radials spread out. Run them from the antenna down to the ground with no slack?
If I were to use the vertical at 20ft with radials, should I just run them to the ground and hold them down(so what ever the height make radials to go from antenna base to ground) or 4 1/4 Wave length radials for each band and if needed use nylon(or something else) to make the difference if they don't reach the ground?
Not used a vertical antenna before(as you will guess) so need some input. Comments or information please.
Thanks
Richard
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RE: Vertical Help
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by k3ky on January 4, 2002
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There is not a single answer to this question because
there are too many variables. The problem is
compounded for a multiband vertical, as an 'optimum'
height for one band may well be anything but optimum
on another band. Ground mounting is always a good
option for verticals. Elevating one slightly may give
slightly greater gain and may slightly reduce the
vertical angle of radiation, but "more is better" is
definitely not the case here. If the antenna is 'too
high' it will suffer from vertical lobe splitting,
and it may happen that the angle of arrival of a
desired signal may fall right into a vertical pattern
null, reducing signal strength. Verticals are fairly
unpredicatable as to performance compared to a
reference horizontal dipole one half wavelength
high. Multiband versions should be viewed as the
compromise antennas that they are. Although they
can do the job in limited space, on the high bands
(20m and up) a reference horizontal dipole will
often beat the pants off of a vertical. Overall, much
depends on the quality of the local earth surrounding
the antenna, over which the owner usually has no
control. With poor ground quality (dry, rocky, etc.),
verticals often do poorly compared to the dipole.
This will be true regardless of the quality or
quantity of any ground radials used. Over sea water,
they are hard to beat. My suggestion: keep it on
or near the ground. 73, David K3KY
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RE: Vertical Help
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by WB2WIK on January 7, 2002
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Actually, a base-fed quarter-wave vertical, even multiband trapped designs like the Hustler BTV series, are highly efficient, equivalent to a center-fed, half-wave vertical dipole, when sufficiently elevated to provide space for sloping 1/4-wave radials drooping ~30 degrees below horizon. This means the vertical _must_ be elevated to accomplish this task.
My 6BTV installed at ~24' above ground at its base, is such an example. I have it installed on an 8' tall roof tower atop the peak of my single-story (15' high) home, with four 1/4-wave radials per band spreading out all over the roof. The slope angle of the radials varies a bit, but in general is about 30 degrees. Because there are 24 radials directly attached to the base of the antenna and spread out as spokes of a wheel might be in all directions, I'm not that concerned about resonances in the metal structure below the antenna (mast and roof tower); however, without such radials, those items would raise a great concern because they would try to act as a radial of compromised length and thus compromise antenna efficiency.
This is the single largest problem I've seen with mast-mounted vertical antennas raised above earth: If the radial system is absent or poor, the mast will be a radial, and can often detune the entire structure. I've come to the rescue of many local hams who couldn't get their vertical antennas to resonate anywhere in the bands, and usually the problem is the mounting mast resonance.
Besides the 6BTV at 24' I have a Tennadyne T-6 LPDA (14-30 MHz) at 55' on a tower, about 50 feet away from the vertical. Switching between the two on bands like 20 meters, 15 meters and 10 meters is often surprising; e.g., the vertical can often outperform the beam, depending upon the path. I would have suspected a problem with the beam, if it weren't for several active ham neighbors having fine antennas (K6SMF, using monoband long yagis at 50-75' on five towers, 1/2 mile away; WB6VIC using an F-12 C3 about 1/4-mile away, et al) whose signals also can sometimes not compete with my vertical, based on direct requested reports from DX stations.
A properly installed vertical can be a wonderful thing. Unfortunately, an improperly installed one can be a shiny aluminum dummy load...
73 de Steve, WB2WIK/6
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