Specifications

SimradSH90
WhatisTVG?
TVGmeansTimeV ariedGain.Asechoeswillbeweakerwhenthedistancetothem
increase,thesonarwillautomaticallyamplifydistantechoesmorethancloseechoes.
Inpractice,thegainwillincreaseinproportionwithhowlongthesonarmustwaitfor
theechoes.
Figure4TheTVGprinciple:Thegainattime(B)islargerthanattime(A)
A
(CD015005-003)
0
1
10 100 1000
B
C
WhenyouchoosetheTVGsettingyoucaneitherswitchitoff,orchoosea“XlogR”
value.Thedifferentsettingsdeterminehowmuchgainthesonarwilluseastimeelapses
alongtheX-axis.Ahighervaluefor“X”willmaketheangle(C)steeper.
Tip
Forscatteredsh,wesuggestthatyouusethe40logRsetting.Forsmallschools,try
30logR,forlargeschools,use20logR.Ifyouuse20logRthebottomwillalwaysbe
presentedwiththesameechostrength.
Ifyouwishtoexamineweakechoesveryclosetoyourvessel,youmaywishtouse
10logRor5logR,orturnofftheTVG.
KeepinmindthattheltersintheSH90areimplementedin“series”.TheTVG
compensationsaremadebeforetheAGC(AutomaticGainControl).Forthisreason,
yourTVGsettingwillalwayshaveaneffectontheAGC.
IfyoudisabletheTVGcompensation,maximumgainwillbeusedonallranges.
WhatisAGC?
AGCmeansAutomaticGainControl.TheAGCwillautomaticallyscalethereceived
echodatatomaintainaproperdynamicrangebasedonalltheincomingechovalues.In
additiontoOff,thestrengthoftheltercanbesettothreedifferentlevels.
TheAGC(AutomaticGainControl)functionadjuststhegainusinganimageprocessing
algorithm.Thisprocessingdependsonthestrengthoftheincomingechosignal.
Theimageisanalyzed,andreverberationandechoesareidentied.Basedonthe
analysis,weakechoesareamplied,whilestrongechoesarereduced.Theresultisa
“normalizing”effectthatreducesnoiseandreverberation.TheAGCisfunctionalupto
102
372739/D