[MLB-WIRELESS] Setup questions

[Tony Langdon, VK3JED]

At 03:19 AM 3/29/2009, hannah commodore wrote:

>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.

Agree, antenna gain should always be increased first.

> > 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.

I've noticed in "real world" settings with lowish antennas that 
omnidirectional antennas seem to perform poorly, compared to 
directional antennas with the same gain specification.  For example, 
I've consistently had worse results with (say) a 9dB omni, versus a 
9dB directional antenna over the same path.  Not sure if this is due 
to reflections (most test areas were urban environments).  If anyone 
wants figures, I'm not sure whether I can get permission to release 
the data, as it was originally for a commercial wifi (using standard 
2.4 GHz equipment) project, which has long since been abandoned.

Another thing I noticed is that fast moving objects in or near the 
path will kill wireless.  During one set of tests, I was running 
15-20 dBi gain antennas pointed at each other over a 1km 
path.  Terrain was flat, but the Geelong Freeway was between the 
antennas.  I could detect the signal (very strong, 30+ dB S/N if I 
recall), but it was impossible to get a viable link working.  I 
suspect the fast moving (vehicular) traffic in the path was 
disrupting the signal.

Just a couple of observations from some real world testing that might 
be of use for this project.

73 de VK3JED / VK3IRL
http://vkradio.com