Can a UDRC hat be used for FreeDV?
FreeDV is a Digital Voice mode for HF radio. You can run FreeDV using a free GUI application for Windows, Linux and OSX that allows any SSB radio to be used for low bit rate digital voice. Alternatively you can buy a SM1000 FreeDV adaptor that allows you to run FreeDV on any HF radio without a PC or sound card.
If you are a hardware or software developer, you can integrate FreeDV into your project using the LGPL licensed FreeDV API.
Speech is compressed down to 700-1600 bit/s then modulated onto a 1.25 kHz wide signal comprised of 16 QPSK carriers which is sent to the Mic input of a SSB radio. The signal is received by an SSB radio, then demodulated and decoded by FreeDV. FreeDV 700C is approaching SSB in it's low SNR performance. At high SNRs FreeDV 1600 sounds like FM, with no annoying analog HF radio noise.
FreeDV was built by an international team of Radio Amateurs working together on coding, design, user interface and testing. FreeDV is open source software, released under the GNU Public License version 2.1. The modems and Codec 2 speech codec used in FreeDV are also open source.
Read more at... FreeDV -- Open Source Digital Voice
Why FreeDV on a Raspberry Pi with a UDRC "hat"?
In a nutshell, you can use it to build HF and VHF/UHF digital radios.
This API will be useful for “embedding” FreeDV into general purpose digital comms applications like fldigi, SDR radios, Android applications, custom embedded devices like the SM1000, or “headless” implementations of FreeDV on platforms like the Raspberry Pi. It needs hardware floating point and at least a 168MHz ARM4 (the SM1000 CPU).
Read more about the API at ...FreeDV API
My thoughts on why UDRC might make a good radio modem card. If we want to add more OFDM subcarriers and improve the voice quality past the proprietary robot-like AMBE (D-star, DMR, Fusion, APCO-25) and carry real data and voice at some real speeds, with FEC and perhaps trellis encoding, we will need more horsepower than a typical USB codec dongle can offer.
This project has not really been opened up to its full potential. FreeDV puts digital voice radio back into the hand of hams and out of the hands of proprietary vendors that are all interested in creating their own market niches (monopolies). Eg. Icom, Motorola, Kenwood, Yaesu, and all the Chinese crap. After experimenting a little with UDRC, I think that UDRC is a step in the right direction for FreeDV.
--Konrad Roeder, WA4OSH