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_collinear_omni_lowpwr/
> 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/tecom02.html
>
> >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
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