50
394149/C
CThepreampliersareverysensitive,andtheycaneasilypickupelectricalnoisefrom
internalandexternalpowersupplies.Theyarealsovulnerableforanaloguenoise
createdbytheirowncircuitry.Digitalnoisecreatedbytheconverterandprocessing
circuitrycanalsocreateproblems.
DA/Dconverterstransformtheanalogueechoestodigitalformat.
ESignalprocessingcircuitrycancreatedigitalnoise.
Selfnoise
Anyvesselequippedwithahydroacousticsystemwillproducemoreorlessselfnoise.
Therearemanysourcesofsuchselfnoise.
•Machinerynoise:Mainengine,auxiliaryengines,gears,pumps,blowers,refrigerator
systems,etc.
•Electricnoise:Electricmotors,groundloops,etc
•Propellernoise:Propellerbladeproperties,cavitation,shaftvibrations,staticdischarges
•Cavitation
•Flownoise:Laminarow,turbulentow,bubbles,etc
•Rattlenoise:Looseparts
•Interferences:Otherhydroacousticsystemsonyourownvessel
Wewillheregointosomedetailsinordertoanalysethedifferentsourcesofselfnoiseona
vesselandhowtheymayinuenceuponthenoiselevelofthehydroacousticinstruments.
Machinerynoise
Themaincontributorisusuallythemainengineonboardthevessel.Thecontributionfrom
auxiliarymachinerymay,however,beconsiderable,especiallyifsomeofitisinpoorshape.
Themachinerynoisecanbetransmittedtothetransducerasa:
•Structure-bornenoisethroughtheshipstructureandthetransducermountings
•Water-bornenoisethroughthehullintothewatertothetransducer
Electricnoise
Modernvesselsarenormallyequippedwithalotofelectricinstrumentssuchas
hydroacousticsystems,radars,navigationsystems,andcommunicationequipment.Any
electricinstrumentsmayinsomecauseelectricalinterferenceandnoise.
Internationalregulationsandcerticationsareusedtocontrolandreducethis,buteventhese
arelimitediftheelectricalsystemsarepoorlyinstalledandmaintained.
SimradEK80
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