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Length of High Gain Antenna visible for LOS

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Anonymous
August 24, 2004 3:23:33 AM

Archived from groups: alt.internet.wireless (More info?)

Here is a new one that I have not seen answered. On a 3rd party, high-gain
omni antenna, such as one +11 dBi available from fab-Corp.com that I am
currently using, is the antenna constructed of connected 1/2 wavelength
segments?

And whether this is correct (or maybe even if it is not) how much of the
antenna must be line of sight to the receiving directional antenna? Is it
the more the better or after a certain length is the signal as strong as
with the full length?

I am connecting condos to an antenna that is partially obscured by a roof -
from some but not all of the condos, about 100-150 feet away.

Thanks.

--
Bob Alston

bobalston9 AT aol DOT com


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Anonymous
August 24, 2004 1:28:45 PM

Archived from groups: alt.internet.wireless (More info?)

On Mon, 23 Aug 2004 23:23:33 -0500, "Bob Alston"
<bobalston9NOSPAM@aol.com> wrote:

>Here is a new one that I have not seen answered. On a 3rd party, high-gain
>omni antenna, such as one +11 dBi available from fab-Corp.com that I am
>currently using, is the antenna constructed of connected 1/2 wavelength
>segments?

No. No sane manufacturer builds vertical colinear antennas that way.
The coax segments are very lossy, the cut lengths are critical, the
number of parts involved make it expensive to build (lots of labour
content), and the antenna ends up twice as long as necessary for the
gain delivered.

Here is a much better design that doesn't have all the problems:
http://www.guerrilla.net/reference/antennas/2ghz_collin...
http://www.tux.org/~bball/antenna/

Commercial antennas may also be fabricated from a circuit board as in:
http://www.LearnByDestroying.com/pics/tecom/slides/teco...

>And whether this is correct (or maybe even if it is not) how much of the
>antenna must be line of sight to the receiving directional antenna?

All of it and then some. If you have only a partial optical line of
sight, I'm sure you do NOT have sufficient clearance. You need
optical plus fresnel zone clearance to get a decent signal. Any
object in the fresnel zone, will cause edge diffraction of the signal
and plenty of loss. However, if you're desperate, the bottom half
wave of a vertical colinear radiates about half the signal, so it's
the bottom part of the antenna that needs the most clearance.

>Is it
>the more the better or after a certain length is the signal as strong as
>with the full length?

The "problem" with a vertical colinear antenna is that the bulk of the
radiation comes from the first half wave section. Half of what's left
gets radiated from the next half wave. Half of what's left after that
comes from the next half wave. Whatever's left is finally radiated
from the top quarter wave section which is usually not very much.

>I am connecting condos to an antenna that is partially obscured by a roof -
>from some but not all of the condos, about 100-150 feet away.

You're about to have a different problem. 11dbi vertical antennas
have very narrow vertical radiation patterns. A -3dB beamwidth of 7.0
degrees is typical.
http://www.pacwireless.com/products/Pawod24.pdf
So, at 150 ft, half your power illuminates a vertical distance of:
vert = 2 * 150ft * tan(3.5deg) = 18ft
At 10ft per floor, that's about 2 floors of the building. It's worse
as you get closer at 100ft. There's also no guarantee that the main
lobe is exactly horizontal. I strongly suggest you look into
directional antennas, with less gain and a wider beam width.


--
Jeff Liebermann jeffl@comix.santa-cruz.ca.us
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 AE6KS 831-336-2558
August 24, 2004 2:10:32 PM

Archived from groups: alt.internet.wireless (More info?)

Bob Alston wrote:

> Here is a new one that I have not seen answered. On a 3rd party,
> high-gain omni antenna, such as one +11 dBi available from fab-Corp.com
> that I am currently using, is the antenna constructed of connected 1/2
> wavelength segments?
>
> And whether this is correct (or maybe even if it is not) how much of the
> antenna must be line of sight to the receiving directional antenna? Is
> it the more the better or after a certain length is the signal as strong
> as with the full length?
>
> I am connecting condos to an antenna that is partially obscured by a roof
> - from some but not all of the condos, about 100-150 feet away.
>
> Thanks.
>
An end-fed antenna is usually an odd number of quarter wavelengths; the
"basic" quarter-wave having the least gain. Additional half-wave sections
added onto the antenna cause the radiation pattern to flatten out - more
signal in the plane perpendicular to the antenna, higher gain.

Antennas always work best when all of the radiator contributes to the
received wave.

Roby
Related resources
Anonymous
August 24, 2004 2:33:38 PM

Archived from groups: alt.internet.wireless (More info?)

On Tue, 24 Aug 2004 09:28:45 -0700, Jeff Liebermann
<jeffl@comix.santa-cruz.ca.us> wrote:

>Here is a much better design that doesn't have all the problems:
>http://www.guerrilla.net/reference/antennas/2ghz_collin...
>http://www.tux.org/~bball/antenna/

Arialix sells a kit:
http://www.aerialix.com/kits/arlx-om2400-all/arlx-om240...


--
Jeff Liebermann jeffl@comix.santa-cruz.ca.us
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 AE6KS 831-336-2558
Anonymous
August 24, 2004 5:01:20 PM

Archived from groups: alt.internet.wireless (More info?)

"Jeff Liebermann" <jeffl@comix.santa-cruz.ca.us> wrote in message
news:47pmi05m2am53qpupfv9s6rpen4o766gkm@4ax.com...
> On Mon, 23 Aug 2004 23:23:33 -0500, "Bob Alston"
> <bobalston9NOSPAM@aol.com> wrote:
>
> >Here is a new one that I have not seen answered. On a 3rd party,
high-gain
> >omni antenna, such as one +11 dBi available from fab-Corp.com that I am
> >currently using, is the antenna constructed of connected 1/2 wavelength
> >segments?
>
> No. No sane manufacturer builds vertical colinear antennas that way.
> The coax segments are very lossy, the cut lengths are critical, the
> number of parts involved make it expensive to build (lots of labour
> content), and the antenna ends up twice as long as necessary for the
> gain delivered.
>
> Here is a much better design that doesn't have all the problems:
> http://www.guerrilla.net/reference/antennas/2ghz_collin...
> http://www.tux.org/~bball/antenna/
>
> Commercial antennas may also be fabricated from a circuit board as in:
> http://www.LearnByDestroying.com/pics/tecom/slides/teco...
>
> >And whether this is correct (or maybe even if it is not) how much of the
> >antenna must be line of sight to the receiving directional antenna?
>
> All of it and then some. If you have only a partial optical line of
> sight, I'm sure you do NOT have sufficient clearance. You need
> optical plus fresnel zone clearance to get a decent signal. Any
> object in the fresnel zone, will cause edge diffraction of the signal
> and plenty of loss. However, if you're desperate, the bottom half
> wave of a vertical colinear radiates about half the signal, so it's
> the bottom part of the antenna that needs the most clearance.
>
> >Is it
> >the more the better or after a certain length is the signal as strong as
> >with the full length?
>
> The "problem" with a vertical colinear antenna is that the bulk of the
> radiation comes from the first half wave section. Half of what's left
> gets radiated from the next half wave. Half of what's left after that
> comes from the next half wave. Whatever's left is finally radiated
> from the top quarter wave section which is usually not very much.
>
> >I am connecting condos to an antenna that is partially obscured by a
roof -
> >from some but not all of the condos, about 100-150 feet away.
>
> You're about to have a different problem. 11dbi vertical antennas
> have very narrow vertical radiation patterns. A -3dB beamwidth of 7.0
> degrees is typical.
> http://www.pacwireless.com/products/Pawod24.pdf
> So, at 150 ft, half your power illuminates a vertical distance of:
> vert = 2 * 150ft * tan(3.5deg) = 18ft
> At 10ft per floor, that's about 2 floors of the building. It's worse
> as you get closer at 100ft. There's also no guarantee that the main
> lobe is exactly horizontal. I strongly suggest you look into
> directional antennas, with less gain and a wider beam width.
>
>
> --
> Jeff Liebermann jeffl@comix.santa-cruz.ca.us
> 150 Felker St #D http://www.LearnByDestroying.com
> Santa Cruz CA 95060 AE6KS 831-336-2558

Thanks for the reply and information. I am still learning - the more I
learn the more I realize I don't understand.

This link is to my web site and has more info on the wireless setup. IT
also has a picture from my condo porch, showing my tin cantenna, and a view
of the marina clubhouse where the WAP is located. At the time of this
picture, the antenna was mounted in a temporary manner at the top of the 2nd
story on the opposite side from me. Worked quite well for the boats, with
only those in extreme left and right of the picture having any reception
problems; those were due to having larger boats obscuring their LOS to the
antenna by their fly bridges. Also worked OK for me with my tin cantenna.
Occasionally I would lose signal. Seemed to be caused by rain and other
unknown forces.

http://members.cox.net/tulsaalstons/my_tin_cantenna.htm

Trying to decide what to do to improve access by the condos. My latest
thought is to raise the antenna even higher so there is clear LOS to all the
condo units. All condo units are on 2nd or 3rd stories (garages below) so
that minimizes the vertical angle. For that I think I need some kind of
extension mast and a longer pigtale. I am currently using the 39-inch
antenna mount from www.fab-corp.com (select Accessories - scroll down to
"universal antenna mount - super long"). It is a nice heavy metal (steel ?)
mount!

--
Bob Alston

bobalston9 AT aol DOT com


---
Outgoing mail is certified Virus Free.
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Anonymous
August 24, 2004 5:09:58 PM

Archived from groups: alt.internet.wireless (More info?)

"Jeff Liebermann" <jeffl@comix.santa-cruz.ca.us> wrote in message
news:47pmi05m2am53qpupfv9s6rpen4o766gkm@4ax.com...
> On Mon, 23 Aug 2004 23:23:33 -0500, "Bob Alston"
> <bobalston9NOSPAM@aol.com> wrote:
>
> >Here is a new one that I have not seen answered. On a 3rd party,
high-gain
> >omni antenna, such as one +11 dBi available from fab-Corp.com that I am
> >currently using, is the antenna constructed of connected 1/2 wavelength
> >segments?
>
> No. No sane manufacturer builds vertical colinear antennas that way.
> The coax segments are very lossy, the cut lengths are critical, the
> number of parts involved make it expensive to build (lots of labour
> content), and the antenna ends up twice as long as necessary for the
> gain delivered.
>
> Here is a much better design that doesn't have all the problems:
> http://www.guerrilla.net/reference/antennas/2ghz_collin...
> http://www.tux.org/~bball/antenna/
>
> Commercial antennas may also be fabricated from a circuit board as in:
> http://www.LearnByDestroying.com/pics/tecom/slides/teco...
>
> >And whether this is correct (or maybe even if it is not) how much of the
> >antenna must be line of sight to the receiving directional antenna?
>
> All of it and then some. If you have only a partial optical line of
> sight, I'm sure you do NOT have sufficient clearance. You need
> optical plus fresnel zone clearance to get a decent signal. Any
> object in the fresnel zone, will cause edge diffraction of the signal
> and plenty of loss. However, if you're desperate, the bottom half
> wave of a vertical colinear radiates about half the signal, so it's
> the bottom part of the antenna that needs the most clearance.
>
> >Is it
> >the more the better or after a certain length is the signal as strong as
> >with the full length?
>
> The "problem" with a vertical colinear antenna is that the bulk of the
> radiation comes from the first half wave section. Half of what's left
> gets radiated from the next half wave. Half of what's left after that
> comes from the next half wave. Whatever's left is finally radiated
> from the top quarter wave section which is usually not very much.
>
> >I am connecting condos to an antenna that is partially obscured by a
roof -
> >from some but not all of the condos, about 100-150 feet away.
>
> You're about to have a different problem. 11dbi vertical antennas
> have very narrow vertical radiation patterns. A -3dB beamwidth of 7.0
> degrees is typical.
> http://www.pacwireless.com/products/Pawod24.pdf
> So, at 150 ft, half your power illuminates a vertical distance of:
> vert = 2 * 150ft * tan(3.5deg) = 18ft
> At 10ft per floor, that's about 2 floors of the building. It's worse
> as you get closer at 100ft. There's also no guarantee that the main
> lobe is exactly horizontal. I strongly suggest you look into
> directional antennas, with less gain and a wider beam width.
>
>
> --
> Jeff Liebermann jeffl@comix.santa-cruz.ca.us
> 150 Felker St #D http://www.LearnByDestroying.com
> Santa Cruz CA 95060 AE6KS 831-336-2558

Incidentally, the antenna I used as the assumption on how the omnis are
built is from the 1st link in the "Design" section on this link you provided
> http://www.tux.org/~bball/antenna/

For easy access by anyone interested, this is the link to the design to
which I was referencing:
http://www.guerrilla.net/reference/antennas/2ghz_collin...


--
Bob Alston

bobalston9 AT aol DOT com


---
Outgoing mail is certified Virus Free.
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