wrote:
I am trying to establish a wireless network for Internet Access, Video
Conferencing and Intranet Applications, I though to use either a
2.4GHz Sector or Omni Directional Antenna would do the job but I can
find any product that goes as far the distance I am trying to cover (a
radius of 20Km). My idea is to use a powerful radio with the Antenna
monted on a tall mast at the location of the internet feed (via VSAT),
this location is idea for LOS at the other locations.

It's probably illegal. In the U.S., EIRP limits are 1w for portable/mobile
units and 4w for fixed (point to point links). For example, the infamous
Pringles can antenna is at the border of illegal for point to point links,
and is definately illegal for mobile or portable use.

I don't know what the EIRP limits are if you are out of the U,S. here
in Israel it's 100mw, effectivly making gain antennas without a long
(high loss) feed line illegal.

About the only way to do it with such a wide radius is a MESH network and
gain antennas with 10db (10x) gain. Using a transmitter power of 100mW
(which is the standard), you will be just at the limit. The extra gain
of the antenna will also help increase the range of the remote units.

A cheap MESH network can be but together using Linksys WRTG54-L routers
(note the "L" suffix) and third part firmware such as TOMATO
(www.polarcloud.com).

You will need to do some inteligent design of the network, you want to
MESH with the least number of hops to your Internet connection.

20 KM, is an awfully long range for a MESH network anyway. If you
have a reliable range of 150 feet (50m) per node, and place them 300m
apart, a strip 20km long by 100m wide would need 50-60 nodes depending
upon terrain, buildings, etc. With a possible 25 hops between a remote
device and the Internet, latency would be too high (it would take too
long) for VoIP or videoconferencing. Web surfing, email, file transfer,
data telemetry, would probably be ok.

WiMax would be better, if it delivers on promised performance, you
would be able to place your nodes as far as 4 miles apart (2m range).

Meanwhile if you can combine a MESH and fiber optic network, you would
get much better results, but at a much higher cost. You no longer would
be able to use cheap routers and there is the cost of the fiber.

Geoff.

--
Geoffrey S. Mendelson, Jerusalem, Israel N3OWJ/4X1GM
IL Voice: (07)-7424-1667 U.S. Voice: 1-215-821-1838
Visit my 'blog at http://geoffstechno.livejournal.com/