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{
    "url": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/email/4KLDWNQKHPHLG33M4POK37YDZTXU35C5/",
    "mailinglist": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/",
    "message_id": "[email protected]",
    "message_id_hash": "4KLDWNQKHPHLG33M4POK37YDZTXU35C5",
    "thread": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/thread/4KLDWNQKHPHLG33M4POK37YDZTXU35C5/",
    "sender": {
        "address": "ross (a) topwire.co.nz",
        "mailman_id": "d9ef72508cbd4a2b812c57a87b7ef26a",
        "emails": "https://mailman.amsat.org/hyperkitty/api/sender/d9ef72508cbd4a2b812c57a87b7ef26a/emails/"
    },
    "sender_name": "Ross Whenmouth",
    "subject": "[amsat-bb] Re: D STAR - try freeDV instead",
    "date": "2013-11-12T07:01:39Z",
    "parent": null,
    "children": [],
    "votes": {
        "likes": 0,
        "dislikes": 0,
        "status": "neutral"
    },
    "content": "Hi,\n\nRather than trying to get a D-Star radio to QSY in less than 5 kHz \nsteps, you could try freeDV with your existing SSB transceivers?\n\nD-Star occupies 6.25 kHz bandwidth on the transponder, but freeDV only \nneeds 1.25 kHz (half of a normal SSB voice emission).\n\nYou can get freeDV (experimental) software here:\nhttp://freedv.org/tiki-index.php\n\n\nUnlike the early days of SSB (which has been the subject of various \npatents) AMBE is unlikely to ever be free, even after the patents expire \nas DVSI Inc. treats AMBE as a TRADE SECRET, and the only way to get the \ncodec is to buy the chip (a locked TI DSP pre-loaded with AMBE). DVSI's \npatents cover some of the technology used in AMBE, but these patents do \nnot explain enough about the AMBE process or protocol for someone to \nwrite their own AMBE-compatible codec.\n\nOnce the patents expire, someone with the right resources might be able \nto hardware reverse engineer the firmware in the AMBE chip (very \ndifficult!) and write a specification of the AMBE process/protocol, \nwhich someone else who has never seen inside the AMBE firmware can then \nuse to write a \"clean room\" AMBE compatible codec. Depending on the laws \nin force at the time, it might also be illegal to de-bond the AMBE chip \nand reverse engineer the codec therein. However, all this is probably \nrequires far more effort than it is worth - better to spend time, energy \nand money on developing an alternate codec that is truly \"open\".\n\n\nFreeDV uses an OFDM modem (16 QPSK carriers + 1 BPSK pilot), designed to \nhave strong resistance to the multi-path propagation typical on the HF \nbands that it was originally intended to be used on. However, this means \nthat is has a ~ 12dB peak to average power ratio, which imposes \nlinearity requirements on the transmit signal path. For satellite \noperation, where path loss is a much greater concern than multi-path, \nthe use of a serial tone modem (single carrier QPSK, BPSK, GMSK, etc) \nfor freeDV would reduce the linearity requirements of the transmit \nsignal path making it easier for an otherwise marginal ground station to \nproduce enough EIRP to work the bird.\n\n\n73's ZL2WRW\nRoss Whenmouth\n",
    "attachments": []
}