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


Stuart Longland VK4MSL
 

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
<http://www.w1hkj.com/Fldigi.html>, 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 <http://www.rowetel.com/?p=3469>

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.

http://www.rowetel.com/?p=5520

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...
...it's backed up on a tape somewhere.

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