Basicintroduction
History
HeinrichRudolfHertz(1857~1894),aGermanphysicist,firstusedexperimentsin1887Theexistenceofelectromagneticwaveswasconfirmed,andapaperwaspublishedin1888.Hemadeagreatcontributiontoelectromagnetism,sotheHertz,theSIunitoffrequency,isnamedafterhim.
Electricity(voltageorcurrent)canbedividedintoDCandAC.Incommunicationapplications,alternatingcurrentisgenerallyusedforsignaltransmission.
Hertzexperimentsprovedthatelectromagneticwavesexist,andthepropagationspeedofelectromagneticwavesisequivalenttothespeedoflight.TheHertzexperimentsopenedupinnovativewaysforthedevelopmentofradioelectronictechnologiessuchasradio,radar,andtelevision.Hestudiedtheinfluenceofultravioletlightonsparkdischargeanddiscoveredthephotoelectriceffect.Hebelievedthatobjectscanreleaseelectronsundertheirradiationoflight.ThisdiscoverybecamethebasisforEinstein'stheoryoflightquantum.
Real-worldapplications
Hertz(hertz)isabbreviatedasHz.Thephysicalmeasurementunitoffrequencyreferstothenumberofperiodicfluctuationspersecond.ThemeasurementunitsofhighfrequencymainlyincludekHz(ie1000Hz),MHz(ie1000kHz),GHz(ie1000MHz),andTHz(ie1000GHz).
Frequencyisthenumberofrepetitions,cyclesorvibrationsofaperiodicprocessperunittime,usuallyexpressedbyf.
Radiofrequencyisusuallymeasuredinkilohertz(kHz)ormegahertz(MHz).
Thepassbandofsingle-modefiberis100GHz/km,andthepassbandofmultimodefibercanexceed10GHz/km.
Unitconversion
Internationalsystemofunitsnotationderivedunits
1kilohertz(kHz103Hz)=1000Hz
1MHz(MHz106Hz)=1000000Hz
1GHz(GHz109Hz)=1000000000Hz
1Terahertz(THz1012Hz)=1000000000000Hz
1BeatHz(PHz1015Hz)=1000000000000000Hz
1Ah(EHz1018Hz)=1000000000000000000Hz
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