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, <dl1...@gmx.de <mailto:dl1...@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
    <yugaljoshi2...@gmail.com <mailto:yugaljoshi2...@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, <willco...@gmail.com
    <mailto:willco...@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
        <yugaljoshi2...@gmail.com <mailto:yugaljoshi2...@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


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