[MLB-WIRELESS] Setup questions

[hannah commodore]

Naz Gassiep wrote:
> I am currently setting up a network for an Islamic Community Centre in 
> Coburg. We are on high ground, and the roof seems to have good line of 
> sight for quite a distance.
> 
> I need some advice. Please excuse the beginner's questions, as I've only 
> ever used wifi in a home and small office setting. Outdoor stuff is all 
> new to me.
> 
> 1. How best to cover a large area with an omni antenna? Is it better to 
> get a 60mW AP and a 20dB antenna, or a 200mW AP and a 15dB antenna? Or 
> does it not make a difference?

If you plan to share the wireless to clients, or have multiple sites
connecting in to this one location, then antenna gain is more useful
than transmit power. This situation is known as Point to Multipoint and
is the method used by commercial wireless ISPs using 802.11 technology.

The reason antenna is more important than power is that with a higher
gain antenna, you also increase the ability to "hear". that is, a remote
client (maybe a laptop) transmitting a weak signal will have that signal
effectively increased with the gain of the antenna. using more transmit
power does not increase the ability to receive, or sensitivity, and they
may receive your packets, but you can't receive theirs.

running more power never hurts though, and can often increase
reliability around the marginal areas. however it adds no benefit if the
client receiving your signal can't be heard by you.

> 2. If I put a max legal omni on the roof, how much of an area can I 
> expect to cover? 100m radius? 1km radius? 10km radius?

depends on the equipment and surrounds. in free space you can account
for ~100dB of loss for 2.4GHz signal at 1km distance, ~94dB at 500m -
which means you have to have effective radiated power at your site +
receiver sensitivity + receiver antenna gain + ~3dB greater than 100dB
to have an effective link for 1km.

here is a guide to help work out path losses:
http://huizen.deds.nl/~pa0hoo/helix_wifi/linkbudgetcalc/wlan_budgetcalc.html

however this doesn't take into account other possible detriments like
refraction from near objects, trees, and even humidity on that day.

> 3. At present, what are the benefits of joining Melb Wireless? 

sharing world of warcraft files without paying for internet usage?

> I've been a subscriber to the list for some time now, and I've seen lots of talk 
> about network topology and link management, but there is very little 
> discussion of why someone would want to join. Would our community centre 
> benefit from joining MW or is MW just a hobby club for network engineers?

MW is often made up of isolated point to point links, without
connections in between. Some sites are well connected, but at the moment
it's not possible to span from one side to the other within MW. You may
have a lot to learn from the people involved, and even act as a conduit
for further MW development. otherwise, MW would have no direct benefit.

> 4. I have a home and a small office in two locations and would like to 
> join them to MW. What is the sort of cost involved with setting up a MW 
> link?

really as much money as you want to put in to it. the *easiest* way to
get started, in my opinion, would be to import some Ubiquiti hardware
from the US. they sell easy to use equipment which comes standard with
power over ethernet, and most of it is weather proof.
the Bullet requires an external antenna and could be plugged in to a
jaycar 2.4GHz dish for very very reliable point to point links.
the nanostation has a sector antenna meant to be clustered in groups of
2 or 3 like a cell phone tower for client connections.

the sky is the limit on how much you are willing spend on the more
advanced hardware

> Regards,
> - Naz.

good luck with the project!

h