Installation manual

SimradES70
YoucanadjusttheTVGsettingusingtheEchogramorTVGfunctions.Botharelocated
ontheActivemenu.
Becausethestrengthoftheechoeswillbecomeweakerwithincreasingdepth,theecho
sounderwillautomaticallyamplifythedeepestechoesmorethantheshallowerechoes.
Infact,thegainwillincreaseproportionaltohowlongtheechosounder“waits”forthe
echoes.WhenyouchoosetheTVGsettingyoucaneitherswitchitoff(whichwedo
NOTrecommended),oryoucanchoosesettings20logRor40logR.
Thevarioussettingscontrolthegainalgorithms,howmuchgaintobeappliedwhen
thedepthincreases.Whenyouchoosethe40logRsetting,thegainwillincreasewith
thedepthmorerapidlythanifyouchoosethe20logRsetting.Thisissimplybecause
individualshesemitsmallerechoesthanaschool,andthismakesthemmoredifcultto
detect.IntheequationthecharacterRmeans“Range”.
Figure37TVGprinciple
(CD010217-004)
20logR
40logR
A A
Theillustrationshowshow
thegainclosetothebottom
(B)islargerthanjustbelow
thetransducer(A).Theechoes
fromtheshclosetothe
bottomwillthenbeshownwith
thesamestrength(colour)as
echoesfrompelagicsh.
Theleftvesselusesthe20log
Rsetting.Duetotheincreasing
beamwidth(C),singleshes
areshownlargerandlargerwith
increasingdepth,eventhough
theymaybeofidenticalsize.
Therightvesselusesthe40log
Rsetting.Thesizeofthesh
willstillappeartogrowlarger
astherangeincreases,buttheechoiscompensateddifferentlytoofferamoreuniform
echostrength(colourintheechogram).
Whenyouarelookingforschoolsthesewilllltheentirebeam,justasthebottom
normallydoes.Alotofgainisthennotnecessary.The20logRsettingwillprovidean
acceptableechostrength.
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