Practical experience with a Cantenna

I am curious. I am considering setting up a temporary antenna for a friend
of mine, however I don't want to invest the time in building a Cantenna if
it most likely won't work for me.

I need to be able to get internet access to someone that is 1 mile away.
The only thing that is disrupting the LOS is about 2000 feet of some pretty
thick trees (which I read to be the worst thing for this application).

Has anyone used a Cantenna through some pretty thick woods? If so, what was
your result?

Thanks!

"Jon Arbuckle" <NOSPAM@Nospam.com> hath wroth:

>I am curious. I am considering setting up a temporary antenna for a friend
>of mine, however I don't want to invest the time in building a Cantenna if
>it most likely won't work for me.
>
>I need to be able to get internet access to someone that is 1 mile away.
>The only thing that is disrupting the LOS is about 2000 feet of some pretty
>thick trees (which I read to be the worst thing for this application).
>
>Has anyone used a Cantenna through some pretty thick woods? If so, what was
>your result?

I live in a very thick over grown oak, redwood and douglas fir forest
and have considerable experience trying to shoot through the trees. I
suggest you give up now. The water in the trees are like a brick
wall. The trunks, are impervious to RF. At one mile, the Fresnel
Zone is about 19ft radius at midpoint. That means you'll need to have
a 38 ft wide hole at midpoint in order for the path to be reliable. It
also means that your antennas at both ends will need to be at least
19ft off the ground.

I've also gone through the trouble of mapping the local access points
and some clients in the area. Using this map, I've played with
various antennas on my rooftop trying to see what works best for
"drilling" through the trees. I've also tried to setup a WISP
(wireless ISP) in a nearby town also full of trees.

What happens is that if you can visually see the other end of the
link, it will work, but may not stay working. For example, we have a
neighborhood WLAN/LAN with about 6 houses on the wireless system. All
are line of sight, and most have at least one tree in the way. I
can't go through the trunks at all. The leaves allow some
penetration, but when it rains, those go dead. The only long shot
that's stable is a 400ft shot with clear line of sight.

I also have a series of point to point links scattered around the
forest using panel and dish antennas. They're also affected by the
weather but have sufficient fade margin to prevent total loss of
signal. The biggest source of unreliability over the years has been
squirrels chewing on the cable and lightning hits.

Even if you get 24dBi dish antennas at each end of the link, you're
going to have problems going through the trees. A can antenna is
about 8-10dBi gain, which is insufficient for a 1 mile link even
without the trees.

--
Jeff Liebermann jeffl@comix.santa-cruz.ca.us
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

Jeff Liebermann wrote:
> "Jon Arbuckle" <NOSPAM@Nospam.com> hath wroth:
>
> >I am curious. I am considering setting up a temporary antenna for a friend
> >of mine, however I don't want to invest the time in building a Cantenna if
> >it most likely won't work for me.
> >
> >I need to be able to get internet access to someone that is 1 mile away.
> >The only thing that is disrupting the LOS is about 2000 feet of some pretty
> >thick trees (which I read to be the worst thing for this application).
> >
> >Has anyone used a Cantenna through some pretty thick woods? If so, what was
> >your result?
>
> I live in a very thick over grown oak, redwood and douglas fir forest
> and have considerable experience trying to shoot through the trees. I
> suggest you give up now. The water in the trees are like a brick
> wall.

<snip>


>
> --
> Jeff Liebermann jeffl@comix.santa-cruz.ca.us
> 150 Felker St #D http://www.LearnByDestroying.com
> Santa Cruz CA 95060 http://802.11junk.com
> Skype: JeffLiebermann AE6KS 831-336-2558

Isn't there some magic relationship between H2O and 2400Mhz? Like water
absorbs the 2.4G RF most efficiently, and thus microwave ovens use this
frequency.

Wifi isn't all that far away in frequency.

miso@sushi.com wrote:
> Isn't there some magic relationship between H2O and 2400Mhz? Like water
> absorbs the 2.4G RF most efficiently, and thus microwave ovens use this
> frequency.
>
> Wifi isn't all that far away in frequency.

Actually that's urban myth. Microwave ovens use 2.4 GHz because its in the
unlicensed ISM band.

[snipped from http://www.answers.com/topic/microwave-1]

Microwave heating is sometimes incorrectly explained as a rotational
resonance of water molecules, but this is incorrect: such resonance only
occurs at much higher frequencies, in the tens of gigahertz. Moreover,
large industrial/commercial microwave ovens operating in the 900 MHz range
also heat water and food perfectly well.

Also,
http://en.wikipedia.org/wiki/Microwave
http://www.zyra.org.uk/microw.htm

decaturtxcowboy wrote:
> miso@sushi.com wrote:
> > Isn't there some magic relationship between H2O and 2400Mhz? Like water
> > absorbs the 2.4G RF most efficiently, and thus microwave ovens use this
> > frequency.
> >
> > Wifi isn't all that far away in frequency.
>
> Actually that's urban myth. Microwave ovens use 2.4 GHz because its in the
> unlicensed ISM band.
>
> [snipped from http://www.answers.com/topic/microwave-1]
>
> Microwave heating is sometimes incorrectly explained as a rotational
> resonance of water molecules, but this is incorrect: such resonance only
> occurs at much higher frequencies, in the tens of gigahertz. Moreover,
> large industrial/commercial microwave ovens operating in the 900 MHz range
> also heat water and food perfectly well.
>
> Also,
> http://en.wikipedia.org/wiki/Microwave
> http://www.zyra.org.uk/microw.htm

Well, that certainly clears up a lot of bull I've been told over the
years. Now if we can just get to the bottom of the Richard Gere gerbil
caper....

<miso@sushi.com> wrote in message
news:1168292887.831533.196190@42g2000cwt.googlegro ups.com...
>
> decaturtxcowboy wrote:
> > miso@sushi.com wrote:
> > > Isn't there some magic relationship between H2O and 2400Mhz? Like
water
> > > absorbs the 2.4G RF most efficiently, and thus microwave ovens use
this
> > > frequency.
> > >
> > > Wifi isn't all that far away in frequency.
> >
> > Actually that's urban myth. Microwave ovens use 2.4 GHz because its in
the
> > unlicensed ISM band.
> >
> > [snipped from http://www.answers.com/topic/microwave-1]
> >
> > Microwave heating is sometimes incorrectly explained as a rotational
> > resonance of water molecules, but this is incorrect: such resonance only
> > occurs at much higher frequencies, in the tens of gigahertz. Moreover,
> > large industrial/commercial microwave ovens operating in the 900 MHz
range
> > also heat water and food perfectly well.
> >
> > Also,
> > http://en.wikipedia.org/wiki/Microwave
> > http://www.zyra.org.uk/microw.htm
>
> Well, that certainly clears up a lot of bull I've been told over the
> years. Now if we can just get to the bottom of the Richard Gere gerbil
> caper....

Microwave ovens were using 2.4Ghz way before people jumped on the 2.4Ghz for
unlicensed radio use. In fact microwave ovens were already listed as being
potential interferers to 2.4Ghz radios.
http://www.zyra.org.uk/microw.htm
Food has a high percentage of water, and water is famously H2O. The molecule
of water has the O (Oxygen) in the middle, and the two H's (Hydrogen) stuck
on it like Mickey Mouse ears at a particular angle (105o). The H's are
positive and the O is negative, so the molecule has a + and - end. It has
"polarity".
Polarised molecules try to line themselves up with the electrical field,
like compass needles trying to point at North.
But because the electrical field is changing 2,450 million times a second
the molecules don't quite have time to line up one way before they have to
try to line up the other way!
So, anything with water in it has all these molecules being moved this way
and that by the electrical field, and heated up.

http://www.ccohs.ca/oshanswers/phys_...ave_ovens.html

The microwave radiation produces heat inside the food in the oven. Heat is
produced when the water molecules in the food vibrate (at a rate of
2,450,000,000 times per second) when the food absorbs the microwave
radiation. The movement of the molecules produce friction which causes heat.
This heat cooks or warms up the food.




>

"decaturtxcowboy" <nope_none_@nowayspam.com> wrote in message
news:O8toh.11976$ZT3.10342@newssvr19.news.prodigy. com...
> miso@sushi.com wrote:
> > Isn't there some magic relationship between H2O and 2400Mhz? Like water
> > absorbs the 2.4G RF most efficiently, and thus microwave ovens use this
> > frequency.
> >
> > Wifi isn't all that far away in frequency.
>
> Actually that's urban myth. Microwave ovens use 2.4 GHz because its in the
> unlicensed ISM band.

Microwave ovens were using 2.4Ghz way before people jumped on the 2.4Ghz for
unlicensed radio use. In fact microwave ovens were already listed as being
potential interferers to 2.4Ghz radios.
http://www.zyra.org.uk/microw.htm
Food has a high percentage of water, and water is famously H2O. The molecule
of water has the O (Oxygen) in the middle, and the two H's (Hydrogen) stuck
on it like Mickey Mouse ears at a particular angle (105o). The H's are
positive and the O is negative, so the molecule has a + and - end. It has
"polarity".
Polarised molecules try to line themselves up with the electrical field,
like compass needles trying to point at North.
But because the electrical field is changing 2,450 million times a second
the molecules don't quite have time to line up one way before they have to
try to line up the other way!
So, anything with water in it has all these molecules being moved this way
and that by the electrical field, and heated up.

http://www.ccohs.ca/oshanswers/phys_...ave_ovens.html

The microwave radiation produces heat inside the food in the oven. Heat is
produced when the water molecules in the food vibrate (at a rate of
2,450,000,000 times per second) when the food absorbs the microwave
radiation. The movement of the molecules produce friction which causes heat.
This heat cooks or warms up the food.

miso@sushi.com wrote:
> Well, that certainly clears up a lot of bull I've been told over the
> years. Now if we can just get to the bottom of the Richard Gere gerbil
> caper....

[snipped from http://en.wikipedia.org/wiki/Gerbilling]

Medical literature, which covers examples of items retrieved from patients'
rectums in extreme detail, has never recorded a case of an animal being
removed from a patient, nor of damage inflicted on a patient's insides due
to rectal insertion of an animal.