• [VK2KFJ] (red) MMDVM board failures

    From VK2KFJ via rec.radio.amateur.modera@21:1/5 to All on Mon Aug 16 01:18:49 2021
    XPost: rec.radio.amateur.moderated, aus.radio.amateur.misc

    VK2KFJ Blog

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    (red) MMDVM board failures

    Posted: 15 Aug 2021 05:10 PM PDT http://vk2kfj.blogspot.com/2021/08/red-mmdvm-board-failures.html


    I have bought a few different MMDVM boards to run with Raspberry Pi, such
    as JumboSpot, the dual HAT boards and some red colour S56AL clones.
    These red boards I found to be best for P25, as the other boards typically
    have too much frequency drift, which makes the other boards like JumpSpot
    work fine for DMR usage, but for P25 usage it is much more critical,
    otherwise you get lots of artifacts in the voice transmissions.
    Anyway, the first board I bought, was working great for P25, after 6 months
    it suddenly stopped receiving transmissions from the RF modem receiver, it
    just ignores any transmission, the Receive light no longer lights up, I
    spent considerable time looking for solder faults under magnifying glass, comparing the circuit diagram to the board, followed the path, but could
    not fix it. So I bought another two of the red boards, tested them, they were working, great I put them both to work, so I could run two different frequency P25 hotspots, about a month or so, one of them dies, no receive
    from the radio modem side, then after 4 months the second board dies,
    again, same fault, receiver stops decoding signals.
    All three boards transmit perfectly. I also configured and tested these
    boards for DMR operation and it is the same deal, receiver does not work, transmits ok in DMR mode. I know it is not the mode. All three boards are
    using the onboard ceramic antenna, so it is not a case of RF overload, as
    it is same IC's and circuit used on my JumboSpot boards.
    These boards are marked as S56AL v2.1 and coloured red. These are NOT
    boards from Alex S56AL, this red board is a chinese clone board based on S56AL's circuit design.
    As it stands, I still running these boards in Tx mode, I can monitor 3 different P25 TG's at once now, as none of the boards can receive, so they won't be talking to each other. In the meantime, I am now looking for
    another MMDVM board that is stable enough for P25 usage and won't fail
    after a few months.
    Here are the pics of the "Red" board. Note: JP1 to external SMA socket
    antenna is not bridged.
    Also Note I added the 4 pin IDC sockets to my boards so I can plugin a OLED display






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    160metre Net

    Posted: 15 Aug 2021 04:21 PM PDT http://vk2kfj.blogspot.com/2021/08/160metre-net.html


    news that Steve VK2STG from south of Cooma runs a daily 160metre SSB net
    on 1860kHz LSB at 8pm eastern

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