Simrad ST90 - Page 82

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Tip
ThemostpracticalwaytousetheAGC(AutomaticGainControl)istorstswitchitoff.
Adjusttheechopresentationusingthenormalgainfunctionalityuntilyouhavethebest
possibleresult,thenactivatetheAGC.
TheAGCworksbestwithevenbackground(homogenousnoiseconditions)andpronounced
targets.Withuniformenvironmentalconditionsyoumaybenetfromstrongcompensation.
However,ifyouarelookingatscatteredsh,reducetheautomaticgaincontrol,andtryto
addnormalgaininstead.
Ifyouworkclosetoothervessels,thenoisefromtheirpropellersmaybemisinterpretedas
echoes.Thiswillalsoreducethevisibilityofotherechoes.Thesameappliesifthebottom
conditionsplaceyourvesselwithdecreasingdepthononesideofthevesselandyourtargets
ontheotherside.Reducetheautomaticgaincontrol.
Ifyouhavealargeschoollocatedclosetoyourvessel(typicallycloserthan150meters)
theschoolgivesyouastrongecho.TheAGCmaymisinterprettheschoolechofornoise.
Reduceordisabletheautomaticgaincontrol.
TheltersintheST90areimplementedin“series”.Thegaincompensationsaremade
beforetheAGC.Forthisreason,yourcurrentgainsettingwillalwayshaveaneffecton
theautomaticgaincontrol.
Procedure
1Clickinanyviewtomakeitactive.
Theactiveviewisidentiedwithathickerborder.
2OpentheActivemenu.
3SelectAGC(AutomaticGainControl).
4Selectavaluefromtheoptionsprovided.
Thechoiceyoumakeisbydefaultonlyappliedtothecurrentlyselected(active)view.
Selectthemiddleofthebuttontoopenasmallmenuwiththeavailableoptions.Select
theleftsideofthebuttontoselecta"lower"'menuchoice.Selecttherightsideofthe
buttontoselecta"higher"'menuchoice.
Relatedtopics
Improvingtherecognitionofshandschoolsusingreceiverlters,page78
SimradST90OperatorManual