Radwin 2000 C PLUS User Manual

RADWIN2000CPlusUserManual Release3.5.70 18‐4
AbouttheFresnelZone Chapter18

Figure18‐1:Fresnelzone
Fresnellossisthepathlossoccurringfrommulti‐pathreflectionsfromreflectivesurfaces
suchaswater,andinterveningobstaclessuchasbuildingsormountainpeaks withinthe
Fresnelzone.
Radiolinksshouldbedesigned toaccommodateobstructionsandatmosphericconditions,
weatherconditions,largebodiesofwater,andotherreflectorsandabsorbersof
electromagneticenergy.
TheFresnelzoneprovidesuswithawaytocalculatetheamountofclearancethatawireless
waveneedsfromanobstacletoensurethattheobstacledoesnotattenuatethesignal.
ThereareinfinitelymanyFresnelzoneslocatedcoaxiallyaroundthecenterofthedirect
wave.TheouterboundaryofthefirstFresnelzoneisdefinedasthecombinedpathlengthof
allpaths,whicharehalfwavelength(1/2)ofthefrequencytransmittedlongerthanthe
directpath.Ifthetotalpathdistanceisonewavelength(1)longerthanthedirectpath,then
theouterboundaryissaidtobetwoFresnelzones.OddnumberFresnelzonesreinforcethe
directwavepathsignal;evennumberFresnelzonescancelthedirectwavepathsignal.
TheamountoftheFresnelzoneclearanceisdeterminedbythewavelengthofthesignal,the
pathlength,andthedistancetotheobstacle.Forreliability,point‐to‐pointlinksaredesigned
tohaveatleast60%ofthefirstFresnelzonecleartoavoidsignificantattenuation.
TheconceptoftheFresnelzoneisshowninFigure 18‐1above.Thetopoftheobstruction
doesnotextendfarintotheFresnelzone,leav ing60%oftheFresnelzoneclear;therefore,
thesignalisnotsignificantlyattenuated.
FormoreaboutFresnelzone,seehttp://en.wikipedia.org/wiki/Fresnel_zone.

Radwin 2000 C PLUS Specifications

General

Brand	Radwin
Model	2000 C PLUS
Category	Radio
Language	English