Flatshovel <Flatshovel.2v8g0n@no-mx.wirelessforums.org> hath wroth:
>I have a question regarding the 24dBi 2.4GHz Wire Grid antenna. What
>kind of range does this antenna have when hooked up to a Linksys WRT54G
>wireless router? The reason I ask is, I don't have a DSL connection
>where I live but my neighbor down the road does, he lives 1.5miles from
>me. However there is a line of trees in the way down the road, and I
>can't get the antennas placed over the tree line, just slightly below
>the tree line. Just using 2 of these antennas and say 2 Linksys WRt54G
>wireless routers, can I make the link? Or do I need to add a power
>booster to each end? If so how much power and what is the FCC legal
>limit on this I have no idea?
Well, I think there's enough info to run the calculations. What's
missing is where the WRT54G routers are mounted. On the antennas or
inside the house. I'll assume that you're going to build an outdoor
enclosure (NEMA box) and hang it on the back of the dish.
See Link Calcs at:
<http://wireless.wikia.com/wiki/Wi-Fi#Link_Calculations>
What we have is:
TX power +15 dBm
TX coax loss 4 dB (3 ft LMR-240 plus a mess of connectors)
TX ant gain +24 dBm
Distance 1.5 miles
RX ant gain +24 dBm
RX coax loss 4 dB (3 ft LMR-240 plus a mess of connectors)
RX sens -84 dBm (at 12Mbits/sec connection)
Fade margin unknown
Under ideal conditions, this give you 6Mbits/sec thruput which should
be more than enough for your DSL connection. If you happen to have a
6Mbit/sec DSL connection, or want to go faster, then the receiver
sensitivity will need to be adjusted according to the table at:
<http://wireless.wikia.com/wiki/Wi-Fi#Link_Calculations>
The idea is to obtain a fade margin (or System Operating Margin) of at
least 20dB. This is directly related to the overall system
reliability. See the table at the above URL.
Plugging the values into:
<http://www.terabeam.com/support/calculations/som.php>
I get a fade margin of 31.3dB which is quite good.
However, don't get all excited quite yet. This is the *BEST* case
calculation. Reality and conspiracy will reduce this considerably.
You must have objects along the line of sight be outside the Fresnel
Zone:
<http://www.terabeam.com/support/calculations/fresnel-zone.php>
That's about 23 ft radius at midpoint. So, the dishes at the end
points should be at least 23 ft above the ground. In addition, you
need a 23ft clearance around the line of sight at midpoint. Do you
have that? If the trees are at midpoint, you don't.
The line of trees are going to be a BIG problem. You didn't specify
if they are dense or thin or how deep. Folliage attenuation can be
estimated but I need data. In general, if you can see through the
trees consistently, especially at trunk level, then you have a chance.
Even so, you're going to have attenutation. You have about 10dB. Lose
it wisely.
--
Jeff Liebermann
jeffl@cruzio.com
150 Felker St #D
http://www.LearnByDestroying.com
Santa Cruz CA 95060
http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
Re: Wireless distance question 
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