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ID:62354509
大小:1.69 MB
页数:32页
时间:2021-04-29
《Amateur Radio Technician Class Element 2 Course …_4724:业余无线电技师班2元课程…….ppt》由会员上传分享,免费在线阅读,更多相关内容在教育资源-天天文库。
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.
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