Frequency Division Multiplex Digital Voice (FDMDV)
The original FDMDV mode uses 1125 HzHertz (Hz), unit of frequency, defined as one cycle per second (1 Hz). bandwidth, and runs on 1450 bpsBits per second (bps) speed. 1400bps is from the open source LPC voice codec, and the 50bps is for textual data. The signal itself consists of 14 DQPSKDifferential Quadrature Phase-Shift Keying subcarriers running at 50 baudBaud (unit symbol Bd) is the unit for symbol rate or modulation rate in symbols per second. with 75Hz spacing between subcarriers and a center BPSKBinary Phase-Shift Keying (1 bit per symbol) carrier with 2x TXTransmit power for auto tuning and frame indication. 7 DQPSKDifferential Quadrature Phase-Shift Keying subcarriers flank each side of the BPSKBinary Phase-Shift Keying (1 bit per symbol) center carrier.
Rowe's version is part of his FreeDV open source Digital Voice software, developed by both David Rowe and David Witten. FreeDV started off with a simple open source implementation of the original FDMDV parameters, with the main difference being the usage of Rowe's own Codec 2 voice codec instead of the LPC Codec. Rowe then modified the parameters so that the signal is more robust against signal propagation issues.
The new mode, dubbed FreeDV 1600, uses 1.3kHz of bandwidth, and operates at 1600bps data rate. 1300 bpsBits per second (bps) is for the Codec 2 coded, and 300bps is Golay FECForward Error Correction. This gives the mode more robustness. The general format of the signal is generally the same as the original FDMDV, but a bit wider.
Original FDMDV Version
FreeDV Version (July 2015)
Voice Sample Comparison
Original voice sample:
- Hobby Level Software
- FDMDV *Note, if it says it cannot find msvcr70.dll, download the dll here (I tested it, its safe, you can use VirusTotal for verification) and place the dll in the folder of the program.
- Free DV Digital Voice software for Ham Radio
- FreeDV QSO 14236.0 kHz
- FDMDV QSO @ 10m band with SV1FXO, SV1EIA, SV1IXP & SV1JGW using SDR Transievers
- FreeDV codec2 contact