Re: Amateur Radio G3RUH AX.25 2FSK

[Yugal Joshi]

Hello Marcus 
Thank you for your explanation 

Also thanks for introducing me with protocols 
I learned from the documentation and your explanation that the AX.25 protocol lacks the ability to correct errors and is not optimized to operate with the noisy channel.

I am very excited to read about NGHam which features error-correcting codes.

Thanks and Regards 

On Wed, 12 Aug 2020 at 17:03, Marcus Müller <mueller@kit.edu> wrote:

Hi Yugal,

well, 2-FSK is relatively easy to demodulate, and you'll probably also
be able to use the existing synchronizer blocks to symbol timing- and
frequency-synchronize.

What will definitely require writing code is handling the ax.25 frame
format.

You **should** look at gr-ax25 (it's gr-ax25, by the way, not gr-25)!
It's good to learn from existing resources. And as said, the framing is
definitely to be implemented in code, so you'll end up building an
external module anyways. Best case: you take the existing gr-ax25, and
add the new mode to it.

Now comes something nobody wants to hear, but it's kind of what you're
bound to get when talking to me about the ax.25 standard:

It's a bad frame format. It has a checksum, but that checksum is not
covered by any error correction. That is a terrible idea, and should
have never been designed that way; you can get way, way, way more
reliable and hence, further-reaching communications when you actually
protect *especially* your checksum with forward error correction.
The only redeeming feature of ax.25 is its widespread usage. If you can
help it at all, especially when designing new systems, don't use it, so
that future generations of hams can use less bad frame formats.

Best regards,
Marcus

On 12/08/2020 12.13, Yugal Joshi wrote:
> Hey Volker
>
> I understand there are ways to implement  it using direwolf.
> I am more concern to solve this problem with GRC and mostly with its core.
>
> Can you help me in figuring  out the procedural  steps to be taken to
> implement a receiver in GRC to decode a signal with G3RUH mode Ax25  and
> 2FSk
>
>
> Thanks  and Regards
> Yugal Joshi
>
> On Wed, 12 Aug 2020, 3:30 pm Volker Schroer, <dl1ksv@gmx.de
> <mailto:dl1ksv@gmx.de>> wrote:
>
>     
>     The master branch is for gr3.9, but there is a gnuradio 3.8 branch
>
>     Another good starting point for ax.25 could be wb2osz/direwolf on
>     github.
>     — Volker
>
>
>
>>     Am 12.08.2020 um 06:31 schrieb Yugal Joshi
>>     <yugaljoshi2002@gmail.com <mailto:yugaljoshi2002@gmail.com>>:
>>
>>     
>>     Hello Jeff
>>     Thanks for replying
>>
>>     From what I learned in last two days in GNU Radio, it looks like
>>     gr-25 is an OOT module.
>>     gr-25 works with GR 3.9 and pybinds and I am using GR 3.8.1.0.
>>
>>     Also I want to implement G3RUH  2FSK AX25 using the core modules
>>     of GRC or programming  new OOTs so that I can improve my learning
>>     curve.
>>
>>     Any help would be appreciated from the community.
>>
>>     Thanks and Regards
>>
>>     Yugal Joshi
>>
>>
>>     On Wed, 12 Aug 2020, 4:45 am Jeff Long, <willcode4@gmail.com
>>     <mailto:willcode4@gmail.com>> wrote:
>>
>>         Have you already take a look at this?
>>         https://github.com/dl1ksv/gr-ax25
>>
>>         On Tue, Aug 11, 2020 at 4:13 PM Yugal Joshi
>>         <yugaljoshi2002@gmail.com <mailto:yugaljoshi2002@gmail.com>>
>>         wrote:
>>
>>             Hello all
>>             I am new to the GNU Radio community.
>>             I am starting an effort to implement a receiver using GNU
>>             Radio for the amateur radio whose transmitter operates in
>>             G3RUH mode with 2-FSK modulation and AX25 data format.
>>             I designed the project to learn GNU Radio as well as to
>>             contribute something to the SmallSat Community of my
>>             institution Indian Institute of Space Science and
>>             Technology (IIST).
>>
>>             Is anyone else working on the same configurations ?
>>
>>             Anyone who can guide me through the procedural steps I
>>             should take to design this receiver(G3RUH mode with 2-FSK
>>             and AX25 data format)?
>>
>>             As a background information :
>>             The AX.25 protocol is a standard for encoding the data
>>             that includes a message header,station callsign,
>>             destination callsign, message and a simple CRC-16.
>>             The system is widely used for position reporting of the
>>             amateur stations
>>
>>             Looking for a directive path to move ahead and a positive
>>             response.
>>
>>             Thanks and Regards
>>             --
>>             Yugal Joshi
>>             B. Tech. Electronics and Communication Engineering
>>             Indian Institute of Space Science and Technology (IIST)
>>             Thiruvananthapuram
>>             Kerala
>>             India  - 695547
>>

--

Yugal Joshi 

B. Tech. Electronics and Communication Engineering

Indian Institute of Space Science and Technology (IIST)

Thiruvananthapuram

Kerala

India  - 695547