Re: Can a UDRC RPI hat be used for FreeDV? #udrc-ii #freedv #hf #vhf #uhf

Konrad Roeder -- WA4OSH

I'm going to try to compile the FreeDV code using Compass Linux, which runs on the Raspberry Pi and UDRC-II hat very well.  It has the drivers for the UDRC-II board.

The PTT line is handled by the UDRC-II rig interface.  I will first try it out on 20 Meter HF - 14.236 MHz by driving my Yaesu FT-857 with it.  I have a 7-inch touch screen display on my Raspberry Pi.  It should very nicely display the FreeDV front panel.  I plan on first using a USB dongle for the mic and speaker.  For the PTT, I will use a spare bit on the UDRC-II card.

Later, I probably use a fancier USB mic.  And the PTT will also be handled through USB.  There's definitely some detail that needs to be worked out.

--Konrad, WA4OSH

On Sun, May 14, 2017 at 10:07 PM, Stuart Longland VK4MSL <stuartl@...> wrote:
On 15/05/17 14:57, Konrad Roeder -- WA4OSH wrote:
> Can a UDRC hat be used for FreeDV?

It should work.  It is actually on my TODO list to get my little
Raspberry Pi going with FreeDV.

At worst, we might need to tell it how to drive PTT, and that should not
be a hard modification.

> 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.

Actually, Codec2 does pretty good and compares favourably to AMBE/IMBE.
It also gives MELPe 600 a run for its money.

That said, the UDRC is fundamentally not much different to the USB codec
dongle.  Where it has a significant edge over the USB dongle is:

- GPIO integration for PTT
- I²S is less CPU intensive than USB
- better RF hardening

You still need to do the FEC/trellis coding/modulation *ON* the CPU.
UDRC won't do that for you.  It may be possible to also do some
modulation using the GPU as a poor man's DSP.

The other option is replacing the TI TLV320AIC3204 chip with the '3254,
which has some DSP capability built-in, although how good that is for
modems is anyone's guess.
Stuart Longland (aka Redhatter, VK4MSL)

I haven't lost my mind...'s backed up on a tape somewhere.


Konrad Roeder
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