Looking for 'Tree' solution

I have two builds 800-1000 ft apart separated by trees, rural area,
hills. Trees inbetween are tall enough that building a 'tower' really
won't solve lack of line of sight.


How can I communicate between two linksys WRT54GSs in this situation?



---
http://marriage.jamessmall.com

(E-Mail Removed) hath wroth:

>I have two builds 800-1000 ft apart separated by trees, rural area,
>hills. Trees inbetween are tall enough that building a 'tower' really
>won't solve lack of line of sight.

Do these two buildings sway 100ft in the wind? If not, is the
distance 800ft or 1000ft? Measure it.

>How can I communicate between two linksys WRT54GSs in this situation?

You ask this as if there were no other alternatives. I suggest you
look into:
1. Fiber optic cable.
2. Coax cable. RG-6/u will work to at least 900ft.
3. Wire. Gel filled CAT5 will work to about 1000ft at 10baseT-HDX.
4. Two wires using SDSL modems. 768KBits/sec maximum.
5. Two cable modems. Some of these (i.e. old Zenith) will talk to
each other with proper configuration.
6. 900MHz. It goes long distances and through the trees. See:
http://www.waverider.com
http://www.avalanwireless.com
http://www.freewave.com

If you insist on using a pair of WRT54GS bridges, then we need to
guess at how much fade margin you're working with. 20dB is a good
target value. See:
http://en.wikibooks.org/wiki/FAQ_for...k_Calculations
for how to do the calculations. I've posted at least 20 such
calculations so I'll just skip the guesswork and just throw in the
numbers. I'll assume that the WRT54GS boxes are fairly close to the
antenna and that you'll use the biggest practical commercially
available antenna (24dBi gain).

TX power = +17dBm
TX coax loss = 4dB (3ft LMR-240 plus a mess of connectors)
TX ant gain = +24dBi
Distance = 0.19 miles (1000ft)
RX ant gain = +24dBi
RX coax loss = 4dB (same at other end)
RX sens = -84dBm (at 12Mbits/sec)
Fade margin = unknown

Plugging into:
http://www.terabeam.com/support/calculations/som.php
I get a fade margin of 51dB which is excellent and about 30dB more
than required. That means you can tolerate about 30dB of added
attenuation from the trees and still have a useable link. I guess
about 20dB attenuation per thick tree so this just might go through
1.5 trees.

Any particular type and size of tree?

Where are the hills? If in between, you need to verify that you have
at least 0.8 times the Fresnel Zone clearance. At 2.4GHz and 1000ft,
you need to have 8ft radius of clearance around the line of sight at
midpoint. That means your antennas have to be at least 8ft off the
ground.
http://www.terabeam.com/support/calc...esnel-zone.php

You're probably not going to like the size of a 24dBi dish antenna. If
you use a much more aesthetic 12dBi panel antenna, the fade margin
drops to 27dB. That will only go through about 1/3 of a tree and
probably won't work.

Light reading on foliage attenuation:
http://michwave.com/bbnetwork/faq/radiopropagation.htm
http://www.avalanwireless.com/assets...oductBrief.pdf

--
Jeff Liebermann (E-Mail Removed)
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558