
SimradSH90
Reception
Agreatefforthasbeenmadetoreduceunwantednoisetogeta
cleanandstableechopresentation.Toachievethisgoalthesonar
receiverhasthefollowinglteringpossibilities:
•FMCorrelationlter
•AGC(AutomaticGainControl)
•RCG(ReverberationControlledGain)
•Ping-to-pinglter
•TVG(TimeV ariableGain)
•Noiselter
FMCorrelationlter
TheFM(frequencymodulation)isasweepinfrequencies.
Thereceiverltersoutthosesignalsthatarethesameasthe
transmitted.Thisprovidesalteringeffect,whichefciently
reducesinterference,noiseandreverberation.Inadditionto
givingacleanandstableechopresentation,thiswillnormally
alsoincreasethesonar’sdetectionrange.Theadvantageof
theFMcorrelationlteristhatitretainsthehighresolutionin
rangewithlongpulselengthsandhighenergy,andthatitisnot
sensitivetomovingtargets.
AGC(AutomaticGainControl)
TheAGC(AutomaticGainControl)sensestheecholevelin
severaldirections,andusethisasabasisforadjustingallthe
receiverbeams.TheAGCwillthusprovideautomaticscaling
ofthedatainordertomaintainproperdynamicrangebasedon
allechovalues
Thestrengthoftheltercanbeselectedinthemenu.
RCG(ReverberationControlledGain)
TheRCGfunctionadjustthepicturetominimizeinuencefrom
bottomandsurfacereverberation.
Thestrengthoftheltercanbeselectedinthemenu.With
maximumstrengthisselected,theRCGwilleffectivelyreduce
thebottominshallowwater,whilevariationsonthebottom
willbedisplayed.Notethatscatteredshcanbeperceivedas
reverberation.TheRCGltermustthereforebeusedwithcareif
scatteredschoolsaretobedetected.
Ping-to-pinglter
TheeSimradSH90isequippedwithaping-to-pinglter(PP
Filter)toprovideacleanandsteadypresentationbyreducingthe
interferenceandnoise.Thisltercomparestheechoesfroma
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