BECKHOFF DK9222-1109-0015 - Manual (Page 6)

I/O
Wireless Automation
Application Note DK9222-1109-0015
. Fresnel zone, attenuation
Fresnel zone
In​radio​transmission,​the​space​between​the​transmitting​and​receiving​antennas​is​known​as​the​Fresnel​zone​(shown​grey​
here).​The​Fresnel​zone​corresponds​to​a​spheroid​between​the​two​antennas​and​should​be​free​of​obstructions​(e.g.​objects,​
houses,​trees,​etc.),​since​the​main​energy​is​transmitted​in​this​area.
​
r
Fig. 5 Fresnel zone describes the space between transmitter and receiver.
Metal​obstructions​in​particular,​such​as​control​cabinets,​machine​parts,​pipes,​iron​girders,​etc.,​disturb​the​formation​of​
the​Fresnel​zone​and​considerably​limit​the​transmission​characteristics.​Each​obstruction​in​the​Fresnel​zone​attenuates​the​
transmission​in​accordance​with​the​size/surface​area​of​the​obstruction.​Reception​may​then​be​disturbed​or​completely​
interrupted​under​certain​circumstances.
However,​if​the​Fresnel​zone​is​free​of​obstructions,​the​propagating​radio​waves​are​attenuated​only​by​the​free​space​
attenuation​and​the​radius​of​the​Fresnel​zone​can​be​determined​in​accordance​with​diagram​1.​The​desired​range​is​plotted​
on​the​x‑axis.​The​resulting​radius​r​can​be​determined​on​the​y‑axis.​The​radius​r​is​also​equivalent​to​the​installation​height​of​
the​antenna.
​
4
3,5
3
2,5
2
1,5
1
0,5
0
0 100 200 300 400 500
r/m
s/m
Diagram 1 Radius r of the Fresnel zone is equivalent to the installation height of the antenna.
New Automation Technology Beckhoff 6
For​application​notes​see​disclaimer​on​the​last​page