Adventures in FreeDV

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DMR, C4FM, P25, D-STAR, NXDN all familiar digital systems in amateur radio. Many contain some element of proprietary software/hardware used in the world of commercial digital radio……until now!

Introducing the all open source, all amateur created FreeDV project. The FreeDV project focuses on digital over HF, however, with the new 800XA and 2020 modes, it now introduces digital at VHF/UHF and SSB Satellite (on the digital transponder of Oscar 100).

I have been experimenting with the 1600 and 2020 modes on 2 meters USB. Myself and Glen G7MNP have been testing out the 2020 mode. This mode is an interesting development in digital radio. Using the leading-edge neural net speech coding (LPCNet), making amateur radio the first to adopt such techniques. It provides 8 kHz wide audio bandwidth while using just 1600 Hz of RF bandwidth.

G7MNP on 144.200Mhz USB FreeDV mode 2020

The mode sounds very different to others and can take a little while to adjust to, certainly using it on 2 meter USB. Depending on the voice it can sound slightly off-pitch. However, when it gets it right it really does and I have to say the results are pretty awesome. The sound is not what we are used to with traditional vocoder processed audio.

Quite a few local stations have purchased the SM1000 which supports the 1600 and 700D modes. I have worked a number of local stations on 2 meters USB using the 1600 mode. These include Glen G7MNP, Mike G4VSS, Vincent M0LCR and Dave G8KBB.

How do I have a go with FreeDV?

Using the GUI is the easiest way to check it out. At the very minimum, you will need to have sound from your radio piped to your computer soundcard (for receiving). The FreeDV GUI software supports most major radios and utilises the hamlib library for PTT control. The 800XA mode uses a 4-FSK modulation and works best on FM mode. 1600 and 2020 work best on SSB, with 700D used by most HF stations. FreeDV adopts the agreed system of LSB on bands below 10MHz and USB on bands above 10MHz.

The usual disclaimer applies. While I try hard to provide the most accurate information, errors can happen. Please feel free to email me any corrections at my address listed on QRZ.com

Links:
https://freedv.org/ – The FreeDV website.
https://github.com/drowe67/freedv-gui/blob/master/USER_MANUAL.md – The FreeDV manual.
http://www.rowetel.com/ – David Rowe VK5DGR’s website about FreeDV and telephony tech.
https://www.florian-wolters.de/ – Florian DF2ET’s site. Lots of digital radio adventures!