Omnidirectional Beam?
 

Is there such a thing as a 2 mtr omnidirectional
vertical beam antenna?

Marvin Rosen wrote:
Is there such a thing as a 2 mtr omnidirectional
vertical beam antenna?

2m antennas that focus radiation in the horizontal are not
usually called beams. They are called phased arrays and some
are very high gain and omnidirectional.
--
73, Cecil http://www.qsl.net/w5dxp



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Marvin,
Depends on what you mean by 'beam'. If you mean a yagi or
quad
type directional antenna, no. If you mean an omnidirectional
antenna
with gain, yes. But if it's an omnidirectional antenna with
gain,
it isn't a 'beam', in the common sense or use of the word, is
it...
'Doc

"Marvin Rosen" wrote in message
...
Is there such a thing as a 2 mtr omnidirectional
vertical beam antenna?



You want an omnidirectional directional antenna?! Nope, there isn't any such
thing.

An omnidirectional antenna radiates equally in ALL directions. If you think
of all the power flowing into an antenna being radiated out, equally
illuminating every unit area of an imaginary sphere around the antenna, then
that's an isotropic radiator. Since ALL the input power is radiated, you
never get any more efficient than that.

If you distort the radiation pattern, so that power isn't equal for every
unit area of that sphere, you now have a directional antenna. You get an
apparent gain in a certain direction because you have "stolen" some power
from other directions. No free lunch, etc.

If you get sloppy with your definition of omnidirectional, you might try to
call something like a quarter-wave vertical rod above a ground plane is an
omnidirectional antenna. Assuming perfect construction, this antenna
radiates equally well in all azimuths. But it sure doesn't radiate equally
well at all elevations. Either way, this isn't a "beam" antenna.

And once you array a group of dipoles or loops to form a classic beam
antenna, you don't have omni-directional radiation vertically or
horizontally.


--
Ed
WB6WSN

Yes, Ed .. but for a beginner, sometimes a picture is worth a lot ..

Ed Price wrote:

"Marvin Rosen" wrote in message
...


Is there such a thing as a 2 mtr omnidirectional
vertical beam antenna?



You want an omnidirectional directional antenna?! Nope, there isn't any such
thing.



Maybe if he visualized a round balloon on a table it might help.
Imagine then taking your hand and pressing it on the top. That squishes
down the top toward the bottom, sorta flattening the balloon. All of
the sides bulge out.

In a way, that is what we are talking about. Everything extra we get in
some direction comes at the expense of some other direction! But if
the earth is the table, looking at it that way, you can reach a lot more
people if you stop reaching for the stars...


W5WQN - I keep forgeeting to add that to my posts in this group, sorry.

--


-- Sleep well; OS2's still awake! ;)

Mike Luther

Uh...no? "Omnidirectional" and "beam" are mutually exclusive terms. It's
either one or the other...You can have a bi-directional beam, but if it's
omnidirectional, it's either not a beam at all, or a really, really poor
one...

- KI6PR

"Marvin Rosen" wrote
Is there such a thing as a 2 mtr omnidirectional
vertical beam antenna?

Ed,
How about a vertical array antenna? It's as omnidirectional
as an antenna can get in a 'real world' situation, and it does
have gain over a single element antenna. Describing it with
the commonly accepted definition of a 'beam' isn't
correct/valid,
(I agree with you there), but it fills the requirements of the
original post (omnidirectional + gain).
'Doc

I figured he meant any omnidirectional gain over a vertical 1/2 wave antenna or
some other reference.

When the "gain" of something is discussed it must always imply a ratio of the
signal strength with respect to some reference.

Common references are a so-called dipole and an isotropic antenna.

For both references you can have omnidirectional gain. My Cushcraft 2-m Ringo
Ranger is omnidirection and has gain.

73 de Jack, K9CUN

"'Doc" wrote in message ...


Ed,
How about a vertical array antenna? It's as omnidirectional
as an antenna can get in a 'real world' situation, and it does
have gain over a single element antenna. Describing it with
the commonly accepted definition of a 'beam' isn't
correct/valid,
(I agree with you there), but it fills the requirements of the
original post (omnidirectional + gain).
'Doc

What do you mean by a "vertical array"? What are the basic radiating
elements, loops or dipoles? And then, how many replications and in what
physical location is this "array"?

Could you be confusing "omnidirectional" with "omniazimuth"? Another poster
visualized this antenna pattern as a squashed (mmmmmmmm) doughnut. Equal
radiation to all points on the horizon, all the way around the compass. But
that pattern isn't omnidirectional. For instance, what about straight
overhead? Is the field as strong there as at the horizon?

Ed
wb6wsn

"Ed Price" wrote in message
news:pxtNb.5617$A74.242@fed1read02...
...Could you be confusing "omnidirectional" with "omniazimuth"?
... radiation to all points on the horizon, all the way around the
compass.
But that pattern isn't omnidirectional. For instance, what about straight
overhead? Is the field as strong there as at the horizon?
______________

The convention in FM/TV broadcasting is to consider only the radiation
directed toward, and for a few degrees below the horizontal plane when
characterising the shape of a radiation pattern as directional or not. This
is the radiation sector that best serves the purposes of the broadcast
station: to provide the strongest signal to the most receivers. Radiation
toward other elevation angles is largely wasted.

Broadcasters use arrays of antenna elements aligned on a vertical axis to
produce maximum gain in, and near the horizontal plane. Typically each of
these elements is omnidirectional in the azimuth plane, arrayed at about 1
lambda vertical intervals, and driven with equal power and phase.

A slide show and tech papers on these topics are available following the
"Papers" button at http://rfry.org.

R. Fry