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</o:shapelayout></xml><![endif]--></head><body lang=PT link=blue vlink=purple><div class=WordSection1><p class=MsoNormal><span lang=EN-US>David Rowe VK5DGR has made available open source software for a 1400 bps HF modem.<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US>FDMDV stands for Frequency Division Multiplexed Digital Voice.<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US>A FDM modem is a basically a bunch of slow modems running in parallel. For example FDMDV has 14 carriers spaced 75 Hz apart, each running at 50 symbols/second. Due to multipath problems on HF this approach works better than one carrier running at 14×50 = 700 symbols/second. On each symbol is encoded two bits using differential QPSK, so the bit rate is 1400 bit/s.<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US>One of the applications of the modem will be Digital Voice since it offers fast sync, no multi-second training sequences, the ability to recover quickly after a fade, and no automatic re-transmit of “bad” packets.<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US>Further information and source code at the FDMDV Modem page<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US><a href="http://www.rowetel.com/blog/?page_id=2458">http://www.rowetel.com/blog/?page_id=2458</a> <o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US>Digital Voice Codec2 mailing list<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US><a href="https://lists.sourceforge.net/lists/listinfo/freetel-codec2">https://lists.sourceforge.net/lists/listinfo/freetel-codec2</a> <o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p></div></body></html>