5 kilometer with 24 Db Parabolic Grid ??

Archived from groups: alt.internet.wireless (More info?)

On Sun, 12 Dec 2004 00:12:13 GMT, purple
<purple.1h4jya@WiFi-Forum_dot_com> wrote:

>i have linksys wap11 and i want to connect to 5 kilometer far AP is the
>24 Db Parabolic Grid (http://www.hyperlinktech.com/web/hg2424g.php) ok
>for that kind of connection?? i mean what will my connection speed?

Well, I've only posted the math for this about 5 times in the last 3
weeks, but it goes fairly quickly. As usual, you didn't supply enough
information to do a decent calculation. Fill in the following.

- Which version WAP11 do you have? The 1.0 and 1.1 versions were
junk. The transmit power and receive sensitivity vary with each
version.

- What access point is on the other end of the link? I'll assume
another WAP11.

- Are you going to have a 24dBi dish at BOTH ends of the link, or
are you trying to connect to something else at the unspecified
access point? I'll assume two 24dBi dishes.

- How much coaxial cable do you plan to use at each end? I'll assume
LMR-400.

- Do you have a clear line of sight including the Fresnel zone
clearance?
http://www.ydi.com/calculation/fresnel-zone.php
At 5km, you need 1.7 meters radius clearance at midpoint.

Since your WAP11v? is limited to 802.11b, your receive sensitivity
will be approximately:
- 11Mbps CCK, -82dBm
- 5.5Mbps CCK, -85dBm
- 2Mbps QPSK, -86dBm
- 1Mbps BPSK, -89dBm
I'm going to arbitrarily decide to try for 5.5Mbits/sec, so the
receive sensitivity will be -85dbm

Plugging into:
http://www.ydi.com/calculation/som.php
Distance = 3.1miles
Tx power = 12dBm
Tx ant gain = 24dBi
Rx and gain = 24dBi
Tx cable loss = 3dB (including connectors)
RX cable loss = 3dB
RX sens = -85dBm (for 5.5Mbits/sec)

This yields a fade margin (SOM) of 25dB. That should work just fine
assuming my guesswork is correct and you don't pickup any multipath or
interference in between the two dish antennas and that you have a
clear line of sight including the fresnel zone. I've also assumed
very little coaxial cable (about 10ft). If you're planning to use
more coax cable, adjust the tx and rx cable losses acordingly. Don't
forget 0.5dB per connector pair plus pigtail losses. I also selected
some rather conservative values for tx power and rx sensitivity that
reflect some of my bench testing on WAP11v1.1 boxes.

A 5.5Mbit/sec connection will give you about 2Mbits/sec thruput (again
assuming there's no interference).


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