Technical information
SimradEK60
Parameters
Observethefollowingdescriptionsofkeyparameters.
Topics
•TVGgainonpage230
•Outputpoweronpage231
•Pulsedurationonpage233
•Rangeselectiononpage235
TVGgain
TVGmeansTimeVariedGain.WhenTVGisusedinanechosounder,wealsosome
timesrefertoitasdepthvariablegain.
ThepurposeoftheTVGfunctionalityistomakeallshesappearwiththesameecho
colourindependentoftheirdifferentdepths.
Inmoretechnicalterms,timevariedgain(TVG)isasignalcompensation.Whenthe
acousticsignalistransmittedfromtheechosoundertransducer,itissubjectedtolossdue
toabsorptionandspreading.First,dependingonthecurrentsalinityandtemperature,
thewaterwillabsorbsomeoftheenergyfromthetransmission.Theabsorptionloss
increasesastherangeincreases.Second,theenergywillspreadouttoformacircular
beam.Thewidthofthisbeamalsoincreaseswiththerange.Bothabsorptionand
spreadingwillthusreducetheenergy,andbothwillalsohaveaneffectonthereturned
echosignal.TheTVGcompensationisdesignedtocounteractthesenaturalphenomena,
andthisisdoneintheEK60usingdigitalsignalprocessing.Thedesiredresultisthat
shofthesamesizereturnechoesofthesamestrength(colour),regardlessofrange.
Becausethestrengthoftheechoeswillbecomeweakerwithincreasingdepth,theecho
sounderwillautomaticallyamplifythedeepestechoesmorethantheshallowerechoes.
Infact,thegainwillincreaseproportionaltohowlongtheechosounder“waits”forthe
echoes.WhenyouchoosetheTVGsettingyoucaneitherswitchitoff(whichwedo
NOTrecommended),oryoucanchoosesettings20logRor40logR.
Thevarioussettingscontrolthegainalgorithms,howmuchgaintobeappliedwhen
thedepthincreases.Whenyouchoosethe40logRsetting,thegainwillincreasewith
thedepthmorerapidlythanifyouchoosethe20logRsetting.Thisissimplybecause
individualshesemitsmallerechoesthanaschool,andthismakesthemmoredifcultto
detect.IntheequationthecharacterRmeans“Range”.
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