19 September 2020
As some of you may know, I am excited about Digital Voice taking off with the HAM radio community. Not so much about the actual communication aspects for me personally, but I love to experiment with the technology that makes it possible to have a globally routed Digital Voice network on the amateur radio bands.
One thing that has been bothering me a lot though, is the closed and proprietary technology used by popular Digital Voice (DV) protocols that are in use today. Protocols such as DMR, D-Star, P.25, TETRA, NXDN, System Fusion, etc. (to name a few) all make use of the proprietary voice codec (coder / encoder, the system that digitizes and compresses human speech).
Yeah you might think “So what? All the off the shelve equipment works out of the box.”. And you know what, you are right. But for people that like to tinker, home brew or just want to do more in-depth experimentation with Digital Voice, this is a serious impediment of running experiments. Sure you can get yourself an AMBE 3000 dongle, that is, if you have at least $299 to spare. Yep, that’s right, a WHOPPING $299 just to enable Digital Voice on your home brew radio project, all disppearing into the pocket of Digital Voice Systems Incorporated. I know what I would rather spend that money on!
Going further, I would even like to argue that because the access to the voice codec is proprietary, and because no specifications are made public by the manufacturer, the Digital Voice frames encoded by this codec are actually encrypted, or at least obfuscated beyond reasonable recognition by listeners not able or willing to pay for a proprietary device. This has nothing to do with amateur radio experimentation, you buy a device, plug it in and operate it. Jay.
Apart from all the financial and legal issues, the AMBE+2 suite of voice codec aren’t all that great anyway, compared to free and open source alternatives like Codec2, Opus or Speex. Especially on bandwidth restricted bands, or operating in less than ideal conditions, getting the most out of the few bits you can transmit is paramount.
Exciting times are ahead!
David Rowe et. al. have been running experiments with Digital Voice on the HF bands using the open source Codec2 Digital Voice codec called FreeDV. FreeDV is a unique player in the Digital Voice arena, because it is 100% free and open source software, including the speech codec. The FreeDV 700D mode can outperform SSB at low signal to noise ratios and the FreeDV 2020 specification can provide 8 kHz of audio bandwidth in just 1600 Hz of RF bandwidth (in comparision: D-Star and DMR require 6250 Hz of RF bandwidth to deliver the same audio bandwidth with less quality).
For the less initiated, a prebuilt SM1000 FreeDV adapter hardware dongle that you put in line with the microphone and phones output is available and for the tinkerers among us there are many home brew options from using micro controllers up to pure software implementations.
You may be also excited to learn that the Es’hail-2 QO-100 satellite can operate in FreeDV 1600 and 2000 Digital Voice mode.
Take a look at what the M17 Project are currently building. Their mission statement leaves no room for wrong interpretations:
The goal here should be to kick the proprietary protocols off the airwaves, replace DMR, Fusion, D-Star, etc. To do that, it’s not just good enough to be open, it has to be legitimately competitive.
The work group is currently finalizing the initial protocol drafts and designing the first hardware specifications. For Digital Voice codec they also make use of the excellent Codec2 from David Rowe.
If you like to get involved with the project, there is an active community over on IRC to discuss the project goals. The project is currently looking for people that can contribute in various ways, take a look at the M17 Project website for more information.
You might argue that the signaling and routing of previously mentioned commercial Digital Voice projects are probably superior to any open standard that may exist today and you are probably right to a large extent. A lot of these systems are in use for emergency services operators, professional user of short range radio, security companies, etc. etc. But please do not forget we are radio amateurs and experimentation and tinkering is actually an essential part of our hobby! Telecom agencies in various parts of the world are already considering removing our primary status on popular bands, due to high bandwidth demands from commercial parties. So join in on the tinkering fun and actually start making use of the generous bands we have been allocated for amateur use!