Bob Bruninga, WB4APR, led a group of radio amateurs earlier this month to Mammoth Cave -- the world’s longest known cave system -- at Mammoth Cave National Park in Kentucky to test how the Automatic Packet Reporting System (APRS) can be used as a means to extend radio communications underground. “When used underground, VHF and UHF radios can only work within a few hundred feet of each other and...
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