Amateur Radio Technician Class Element 2 Course …_4724：业余无线电技师班2元课程…….ppt

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1、TechnicianLicensingClassWeakSignalPropagationSection10WeakSignalPropagationT5C7Radiowavesisausualnameforelectromagneticwavesthattravelthroughspace.ElectromagneticwavesareRADIOWAVESWeakSignalPropagationT3C10Thedistanceatwhichradiosignalsbetweentwopointsareeffectivelyblocke

2、dbythecurvatureoftheEarthistheradiohorizon.VHF&UHFradiosignalswillgenerallytravel“lineofsight.”VHF&UHFradiosignalsareblockedbythecurvatureoftheEarth.WeakSignalPropagationT3C11VHFandUHFradiosignalsusuallytravelsomewhatfartherthanthevisuallineofsightdistancebetweentwostatio

3、nsbecausetheEarthseemslesscurvedtoradiowavesthantolight.Knife-EdgePropagationT3C5Theterm"knife-edge"propagationreferstosignalsthatarepartiallyrefractedaroundsolidobjectsexhibitingsharpedges.WeakSignalPropagationT3C6Troposphericscatterisresponsibleforallowingover-the-horiz

4、onVHFandUHFcommunicationstorangesofapproximately300milesonaregularbasis.T3C8Temperatureinversionsintheatmospherecauses"troposphericducting".TroposphericDuctingWeakSignalPropagationT3C3AcharacteristicofVHFsignalsreceivedviaauroralreflectionisthatthesignalsexhibitrapidfluct

5、uationsofstrengthandoftensounddistorted.IncomingsignalsfromadistantstationheardhundredsofmilesawaywillsoundflutteryanddistortedbyauroralbounceWeakSignalPropagationT3C7The6meterbandisbestsuitedtocommunicatingviameteorscatter.LeonidsandGeminidsmeteorshowersprovidethesecondi

6、tionsBouncesignalsoffmeteortailWeakSignalPropagationT3A11Theionosphereisthepartoftheatmospherethatenablesthepropagationofradiosignalsaroundtheworld.T3C9Duringdaylighthoursisgenerallythebesttimeforlong-distance10meterbandpropagation.WeakSignalPropagationT3C2WhenVHFsignalsa

7、rebeingreceivedfromlongdistancesthesesignalsarebeingrefractedfromasporadicElayer.Sporadic-ErefractionsoffionizedpatchesoftheionosphericE-layerarecommoninsummeron6-meters.WeakSignalPropagationT3A9Acommoneffectof"skip"reflectionsbetweentheEarthandtheionosphereisthepolarizat

8、ionoftheoriginalsignalbecomesrandomized.Skiphappenswhensignalsrefractandreflectofftheionosphere.