The Cruising Club of America have published an updated document that describes in detail the Digital Selective Calling (DSC) system for VHF and SSB radios, and its use in Search & Rescue areas around the world. Click here to download this valuable document, which also includes an up-to-date implementation schedule for the USCG's 'Rescue 21' DSC network
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http://www.cruisingclub.org/pdfs/dl....om_dsc_sar.pdf