400m NLOS link

[snow93]

Hi all... what would be the best setup (antennas etc.) for a non-line-of-sight link (buildings, trees, you name it), using the 2.5gHz (is this correct?) part of the spectrum, over a distance of 400 metres?

Ideally on one end there would just be a laptop with a particularly powerful USB device.

For the other end, I have a linksys wrt54g available, to which can be attached all sorts of antennae, I just have no idea which one! The antenna could easily be mounted on the roof if that is required.

[ad5mb]

Ideally on one end there would just be a laptop with a particularly powerful USB device.

A powerful USB device is not the answer. receive side sensitivity is typically -82 dBm. A more powerful transmitter does not make the receiver more sensitive. If the receiver is not more sensitive, a more powerful transmitter is a waste.

Calculations indicate that a 15dB antenna should return a ~60 db signal strength. This is using a standard Linksys router and a typical laptop.

http://www.terabeam.com/support/calculations/som.php#calc

15 dB is the practical limit for Yagis and patch antennas. if you want more gain than 15 dBi, you want a dish.

A patch would be easier to mount behind a window, less obtrusive outside. In terms of performance, any directional antenna of X gain behaves very much like any other directional antenna of the same gain.

[snow93]

Sorry, I'm slightly new to this...what does db mean? is it related to distance?

Thanks for the answer though - I actually understood the rest of it :-)

[Planet]

[QUOTE=snow93]what does db mean? is it related to distance?
QUOTE]

dB = decibel (http://en.wikipedia.org/wiki/Decibel) ;)

[nosnhojnod]

400m with trees, buildings, etc, good luck. It sounds as though you want to roam and those are obsticles that a PTP (Point-to-Point) has issues with. That gives a narrow beam, and with what you are looking at is a client session. Best of luck. Understand that depending on how many of these obsticles you are looking at the Db loss will be multiplied as you go.

I am not even a fan of NLOS PTP links, client sessions, even worse. By the way I think you meant 2.4 GHz. Once 802.11n is through ratification you may find that a bit better to connect because it will live a bit better in that enviroment, but I will leave you with "best of Luck".