Specifications

Sonartheory
thesonar’smaximumrange.Asshowinthemenu,theAGChasfourdifferentsettings.
Thesesettingsdenethedifferencebetweenthemaximumandminimumecholevelfor
theltertotakeeffect.
Tip
ThemostpracticalwaytousetheAGC(AutomaticGainControl)istorstswitchit
off.Adjusttheechopresentationusingthegainuntilyouhavethebestpossibleresult,
thenactivatetheAGC.
TheAGCworksbestwithevenbackground(homogenousnoiseconditions)and
pronouncedtargets.WithuniformsonarconditionsyoumaybenetfromstrongAGC
compensation.However,ifyouarelookingatscatteredsh,reducetheAGC,andtry
toaddgaininstead.
Ifyouworkclosetoothervessels,thenoisefromtheirpropellersmaybemisinterpreted
asechoes.Thiswillalsoreducethevisibilityofotherechoes.ReducetheAGC.The
sameappliesifthebottomconditionsplaceyourvesselwithdecreasingdepthonone
sideofthevesselandyourtargetsontheotherside.
Ifyouhaveverystrongechoesfromalargeschoollocatedclosetoyourvessel(typically
closerthan150meters),werecommendthatyoureduceorswitchofftheAGC.Thisis
becausetheAGCltermisinterpretstheschoolfornoise.
KeepinmindthattheltersintheSH90areimplementedin“series”.Thegain
compensationsaremadebeforetheAGC.Forthisreason,yourgainsettingwillalways
haveaneffectontheAGC.
WhatisthePPFilter?
PPFiltermeansPing-to-Pinglter.Whenthisfunctionisactivated,thesonarwill
comparetheechoesfromonepingwiththeechoesfromthenextpings.Ifanechois
presentattherstping,butthendisappearsatthenext,thesonarwillinterpretthisas
noiseandreverberation,andsuppressit.
IfyouchoosesettingWeak,thesonarwillonlycomparetwoconsecutivepings.If
youchoosesettingsMediumorStrongthesonarwillcomparefourandeightpings
respectively.
Aboutpulseformandlength
OntheSH90sonar,youcantransmitsoundmodulatedas
•FM
•CW
FMmeansfrequencymodulated,whichmeansthatthefrequencyofthetransmittedpulse
ischangedduringthetransmission.Inmostcasesthismethodwillprovidebetterecho
presentationandstability,andyouwillavoidexcessivenoiseandreverberation.
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