Simrad ST90 - Adjusting the TVG (Time Variable Gain) Setting; Adjusting the Sonar Range

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AdjustingtheTVG(TimeVariableGain)setting
Whenanacousticpulseissentthroughthewater,itwillgraduallyloseitsenergy.The
greaterthedistancebetweenthetransducerandthetarget(s),thegreaterthelossofenergy.
TVG(TimeVariableGain)compensatesforthelossofacousticenergyduetogeometric
spreadandabsorption.
Context
TheTVG(TimeV aribleGain)compensationisdesignedtocounteractthenatural
phenomenaofgeometricspreadandabsorptionloss.IntheST90,theTVGcompensationis
madeusingdigitalsignalprocessingsoftware.TheTVGcompensationisexpressedasa
logarithmiccurve.Eachcurvehasadifferentslopecreatingadifferentgaincompensation.
EachcurveisidentiedwiththeequationXlogTVG.Thecoefcient"X"isaninteger.
Typicalvaluesfor"X"are10to40.
Procedure
1Clickintheviewyouwanttoactivate.
Thesettingyouchoosewillonlybevalidfortheactiveview.Theactiveviewis
identiedwithathickerborder.
2OpentheActivemenu.
3LocatetheTVGbutton.
4Select[+]or[-]tochoosetherequestedsetting.
Relatedtopics
Controllingthegainandrangesettings,page61
Adjustingthesonarrange
Someechoesareclose,othersarefurtheraway.Itisoftennecessarytoadjusttheradiusof
thesearcharea.OntheST90,thisisreferredtoasrange.
Context
TheRangesettingdeneshow"far"youwishtheST90todetectechoes.Inotherwords,you
specifythehorizontalorverticaldistancefromthevesseltotheouteredgeofthesearcharea.
Operatingprocedures