ARLA/CLUSTER: FDMDV Open Source 1400 bps HF Modem

[João Gonçalves Costa]

David Rowe VK5DGR has made available open source software for a 1400 bps HF modem.

FDMDV stands for Frequency Division Multiplexed Digital Voice.
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.

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.

Further information and source code at the FDMDV Modem page
http://www.rowetel.com/blog/?page_id=2458

Digital Voice Codec2 mailing list
https://lists.sourceforge.net/lists/listinfo/freetel-codec2

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