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Hello guys,

I'm revising my notes for the CWNA exam and have found a bit about fresnel zones in outdoor links -

I've read from more sources that "the obstruction can not be more than 40%, and it's better to stick to max of 20%" because of destructive interference.

Now the question just to be sure - is this figure referring to the bottom half of the fresnel zone ?

(It does make sense since I'd expect the obstructions on outdoor links to be coming from the bottom of the link, but... : ) )

Thanks,
Matus

The Fresnel zone is shaped like an American Football, with the transmitter on one end and the receiver on the other.

The Fresnel zone need 60% open on all sides, not just the bottom. In cities is is quite common to have the "sides" of the Fresnel zone obstructed due to tall buildings. Yes, usually is is the bottom that we have to worry about, but it all matters equally.

GT

Thanks GTHill, since so far I haven't installed an outdoor link, I've never thought of side interference from buildings.

Nevertheless, I now have a clear image.

Thanks again :)