On the yard around my house I have two possible spots where to erect a
multiband vertical, an HF6V.
On the first spot it is possible to lay down a symmetrical net of
radials as long as the antenna is tall, but the antenna will be close
to buildings on tree sides, at a distance about two to four times the
antenna height. Buildings in Italy are built by rinforced concrete
with a lot of steel inside, so I expect there will be some effect to
the antenna efficiency and radiation pattern.
On the second spot, the antenna can be more clear of buildings, but
the radials pattern is not symmetrical because il is limited to a
strip of land wide half the antenna height.
So now is my question: if a tradeoff must be made, what is more
important, to have an antenna on the clear or to have the best ground
radials system ?
A second question: is it possible to estimate the effect of ground
symmetry and of buildings presence on the antenna radiation pattern
using antenna simulation software like eznec ?

Thanks to all
Giovanni
IZ0SQZ

So now is my question: if a tradeoff must be made, what is more
important, to have an antenna on the clear or to have the best ground
radials system ?

better to have the radiating part of the antenna clear. The ground
radials, as long as they are numerous, are less critical


A second question: is it possible to estimate the effect of ground
symmetry and of buildings presence on the antenna radiation pattern
using antenna simulation software like eznec ?


Yes.. to a certain degree

What you can do is put in wires where the building is (like a wireframe
drawing), and then see if there's very much current in those wires, when
the antenna is excited. Small current = little effect.

You can get fancier and try and model the building as a grid of wires
which are very resistive, but I'd start with the simple wireframe and
see what it gives you.

What you're really getting isn't a precise model, but more of a
qualitative assessment of whether there is a problem.

On Mon, 19 Jul 2010 11:58:02 -0700 (PDT), Gsat
wrote:

So now is my question: if a tradeoff must be made, what is more
important, to have an antenna on the clear or to have the best ground
radials system ?

Hi Giovanni,

The best solution is both - in the clear with a lot of radials. The
next best is to raise your antenna, if you can. After that, and
assuming the antenna is ground mounted; then use as many radials as
you can (12 or more); as long as you can make them (usually as long as
the antenna is tall is enough); filling as much area as you can.

Multiband verticals are usually designed to be up at least 3 meters.
Multiband verticals are usually poor performers on their lowest band.

A second question: is it possible to estimate the effect of ground
symmetry and of buildings presence on the antenna radiation pattern
using antenna simulation software like eznec ?

Yes. Do it one band at a time to keep it simple. You will be able to
see the effect, but it won't really amount to much UNLESS you are
comparing very few radials (2,3 or 4) to 12 or more; or to 120. The
change from 2 to 12 will be more significant than changing from 12 to
120.

You will also see the change in shape of the antenna pattern's
azimuth. It may seem significant, but in reality, it will be
overshadowed by other effects like the proximity of buildings.

Modeling the effect of buildings takes a lot of time and experience.
Antenna modelers are an extension of your design capability, not a
substitute.

73's
Richard Clark, KB7QHC

On Jul 19, 1:58*pm, Gsat wrote:
On the yard around my house I have two possible spots where to erect a
multiband vertical, an HF6V.
On the first spot it is possible to lay down a symmetrical net of
radials as long as the antenna is tall, but the antenna will be close
to buildings on tree sides, at a distance about two to four times the
antenna height. Buildings in Italy are built by rinforced concrete
with a lot of steel inside, so I expect there will be some effect to
the antenna efficiency and radiation pattern.
On the second spot, the antenna can be more clear of buildings, but
the radials pattern is not symmetrical because il is limited to a
strip of land wide half the antenna height.
So now is my question: if a tradeoff must be made, what is more
important, to have an antenna on the clear or to have the best ground
radials system ?
A second question: is it possible to estimate the effect of ground
symmetry and of buildings presence on the antenna radiation pattern
using antenna simulation software like eznec ?

Thanks to all
Giovanni
IZ0SQZ

I think I'd rather have the one in the clear. What you can do is
use shorter radials in the directions with less room along
with the longer ones in the better directions. Most of the
ground loss with a monopole is at the immediate base of
the radiator. So the shorter radials should help more than
one might think. But I think it would be worth it to get away
from the wire laden buildings.
Actually, I would prefer to elevate the antenna on a mast,
but I don't know if that is an option.
Elevating gives a much better line of sight, but also greatly
reduces the number of radials needed to reduce ground loss.
If the vertical is high enough in wavelength, one radial is all
you really need for an efficient antenna. Two is the minimum
number needed to have a good omnidirectional pattern if you
run them out ground plane style 180 degrees apart.
One with a single radial acts more like a dipole than a vertical.
If the radial can drop down, you have a half wave vertical with
an omnidirectional pattern, but most will be using metal masts
to support the elevated vertical, and will have to fan it out
ground plane style. And that will skew the pattern a tad, but
not hugely so.
Of course, if you elevated a HF6V, you would need at least
one tuned radial for each band to use it on all bands.

On Mon, 19 Jul 2010 11:58:02 -0700 (PDT), Gsat
wrote:

On the yard around my house I have two possible spots where to erect a
multiband vertical, an HF6V.
On the first spot it is possible to lay down a symmetrical net of
radials as long as the antenna is tall, but the antenna will be close
to buildings on tree sides, at a distance about two to four times the
antenna height. Buildings in Italy are built by rinforced concrete
with a lot of steel inside, so I expect there will be some effect to
the antenna efficiency and radiation pattern.
On the second spot, the antenna can be more clear of buildings, but
the radials pattern is not symmetrical because il is limited to a
strip of land wide half the antenna height.
So now is my question: if a tradeoff must be made, what is more
important, to have an antenna on the clear or to have the best ground
radials system ?
A second question: is it possible to estimate the effect of ground
symmetry and of buildings presence on the antenna radiation pattern
using antenna simulation software like eznec ?

Thanks to all
Giovanni
IZ0SQZ

As usual, I cannot recall the source, but I read somewhere that the
symmetry and general layout of the radial field (buried radials) has
little effect on the radiation pattern. I do recall that I considered
the source credible.

I think there is a release of the NEC engine that supports ground
models but I don't know if that will answer this question.
Unfortunately it is priced beyond this hobbyist's budget.

There may be more than two choices. Don't overlook placing the antenna
between these two extremes.

John Ferrell W8CCW

On 19 jul, 20:58, Gsat wrote:
On the yard around my house I have two possible spots where to erect a
multiband vertical, an HF6V.
On the first spot it is possible to lay down a symmetrical net of
radials as long as the antenna is tall, but the antenna will be close
to buildings on tree sides, at a distance about two to four times the
antenna height. Buildings in Italy are built by rinforced concrete
with a lot of steel inside, so I expect there will be some effect to
the antenna efficiency and radiation pattern.
On the second spot, the antenna can be more clear of buildings, but
the radials pattern is not symmetrical because il is limited to a
strip of land wide half the antenna height.
So now is my question: if a tradeoff must be made, what is more
important, to have an antenna on the clear or to have the best ground
radials system ?
A second question: is it possible to estimate the effect of ground
symmetry and of buildings presence on the antenna radiation pattern
using antenna simulation software like eznec ?

Thanks to all
Giovanni
IZ0SQZ

Hello Giovanni,

My first impression is for 80m go for the good ground site and for the
upper bands go for the clear area. From a man made noise perspective,
I would go for the clear area, but of course this one you can check
via S/N ratio of received stations. The clear area may result in less
interference from your signal in user equipment.

Regarding the buildings, are they very large in horizontal size and
height or do I have to think of just three isolated buildings without
any other buildings behind it (seen from the antenna)? If there were
many buildings, I would go for the clear area in both cases.

Regarding radiation pattern, I would not worry about this. If you can
put the antenna such that you have most of the long radials in two
opposite direction only, the effect on radiation pattern is
negligible.

For the DX case, you will rely on the vertical component only as the
horizontal component will vanish more rapidly under decreasing
elevation angle. Your radiation pattern (elevation pattern under
varying azimuth) depends heavily on ground properties several
wavelengths away from the antenna and you have no influence on that.

Best regards,

Wim
PA3DJS
www.tetech.nl
without abc, PM will reach me very likely.

Thanks to all for the good advice. You all agree that the priority is
to have the antenna on the clear.
To summarize , I would exclude the option to elevate the antenna
because I do not like to walk on roofs or climb towers any more, a
ground level antenna is much more safe.
About the ground radials, my understanding is that the RF current
flowing in to the antenna from one terminal of the feed line, must
return to the second terminal of the feed line that is grounded at the
antenna base, and it will do so flowing through the soil in the
vicinity of the antenna. If I provide a more conductive path on the
soil by laying radials, the electrons will find it, regardless of the
simmetry of the system and avoid to dissipate energy heating up the
ground.
On the other hand, a building near the antenna is not connected to the
second terminal of my feed line and so the RF current captured by the
building metallic structures can only be dissipated and playing funny
games with the electronics gadgets inside the building.
Now that I decided to put up a new antenna, let's just hope the solar
cycle 24 will behave.


Thanks to all
Giovanni
IZ0SQZ