Channel Coding in FreeDV

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Naveed Ahmad Chughtai

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Aug 29, 2022, 10:41:00 PMAug 29
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I am using an external radio which performs all digital signal processing (FEC, Scrambling, RF modulation etc) on its input signal. Do i still need FEC coding to be used in FreeDV? What if I remove it from FreeDV and use the one which already implimented in my radio? Guidance is required Please.

Al Beard

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Aug 30, 2022, 4:03:22 AMAug 30
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Hi Naveed,

The main purpose of FreeDV is HF or Short Wave communications.

Limiting the transmitted bandwidth to around 1KHz.

And, the FreeDV app does the whole process. SSB input to voice and back.

HF signals bounce around the ionosphere and there are multiple reflections making the
signal vary enormously. Thus the data error rate is awful but a human can ignore the
errors and communication is successful.

If you want to combine Voice and Data, take a look at the M17 project, a VHF/UHF project.

You did not mention your radio manufacturer nor the frequencies it uses.

So, please mention that, in particular the frequencies and mode it uses.

Alan B


On Mon, 29 Aug 2022 19:41:00 -0700 (PDT), Naveed Ahmad Chughtai wrote
> I am using an external radio which performs all digital signal processing (FEC, Scrambling, RF modulation etc) on its input signal. Do i still need FEC coding to be used in FreeDV? What if I remove it from FreeDV and use the one which already implimented in my radio? Guidance is required Please.
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Mooneer Salem

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Aug 30, 2022, 4:33:40 AMAug 30
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AFAIK M17 is voice only, but I could have missed something.

Also, 2020C mode is 2KHz wide (not to mention that there are other modes that are wider than 1KHz).

-Mooneer K6AQ

Tony Langdon

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Aug 30, 2022, 6:07:47 AMAug 30
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On 30/8/22 6:33 pm, Mooneer Salem wrote:
> AFAIK M17 is voice only, but I could have missed something.

M17 has a few modes of operation:
- voice only (Codec2 3200)
- mixed voice/data (Codec2 1600 + data)
- "packet mode (data only).

Packet mode was recently demonstrated using SDRAngel to send and receive
a text message over M17.

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Mooneer Salem

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Aug 30, 2022, 11:30:57 AMAug 30
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The more you know :) Thanks Tony for the clarification!

-Mooneer K6AQ

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