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Most likely Water damage,
Water gets into the coax and into connectors and connections and connecting devices outside.
To Prove reception connect a NEW Continues length of coax to the antenna and run the coax through a open door or window direct to 1 Tv.
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For outside coax use the coax that has the Compression type connectors on the ends of the coax , not the crimp type connectors.
And to make Double Sure that water does not get into outside connections , Wrap with ,
http://www.coaxseal.com.