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{
    "url": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/email/DTWN5U5BK2TQVUFBQAVHCIR2E2AWA3FB/?format=api",
    "mailinglist": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/?format=api",
    "message_id": "[email protected]",
    "message_id_hash": "DTWN5U5BK2TQVUFBQAVHCIR2E2AWA3FB",
    "thread": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/thread/JFU3VT5GR6KEZYNLJ3GSCCKYOHD4WJWA/?format=api",
    "sender": {
        "address": "daniel (a) destevez.net",
        "mailman_id": "c2eac82b839b45f5a7d3b923c1721007",
        "emails": "https://mailman.amsat.org/hyperkitty/api/sender/c2eac82b839b45f5a7d3b923c1721007/emails/?format=api"
    },
    "sender_name": "Dani EA4GPZ",
    "subject": "Re: [amsat-bb] Outernet L-Band now carries AMSAT and ARISS weekly bulletins",
    "date": "2018-03-17T15:16:20Z",
    "parent": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/email/ZFXJTYNLMMQSAQL3C6AFEXWVIXMG2PCF/?format=api",
    "children": [],
    "votes": {
        "likes": 0,
        "dislikes": 0,
        "status": "neutral"
    },
    "content": "El 14/03/18 a las 20:40, Daniel Cussen escribió:\n\n> I would hesitate to recommend this system, as it is vapour-ware at the\n> moment, and all the previous kits/hardware released have been dropped\n> and made obsolete by changes to the broadcast. Previous broadcasts\n> were 12Ghz geostationary, but decoded using a DVB-S tuner demodulator,\n> then they changed to L-band low earth orbit immarsat and now they are\n> back on geostationary, this time with a new modulation scheme making\n> pointing easier. They are using the \"LoRa\" standard, basically just\n> using a protocol that allows low signal margin decoding ( Chirp Spread\n> Spectrum modulation (CSS) which trades data rate for sensitivity\n> within a fixed channel bandwidth. ), similar to WSJT/PSK31 and other\n> low data rate weak signal modes.\n> \n> It is interesting they thing that a bare LNB (about 80 degree beam\n> width) that seems to be doing the trick, although they also show\n> pictures of patch antennas which presumably are designed for narrower\n> beam width more suited to this.\n\nHi Daniel,\n\nI also find it a bit hard to believe that the current Outernet goal can\nbe made to work: a 30kbps stream from a GEO Ku-band satellite that can\nbe received with a bare LNB or small patch antenna. This is not\nnecessarily impossible if you run the numbers, but its feasibility is\npretty borderline. I'll believe it when I see it working.\n\nAs I understand, one of the main issues they're having is co-channel\ninterference. This goes as follows: if you look at link budget alone\n(free space path loss, the gain of an LNB and so on), maybe things can\nlook OK. However, in the real world what happens is that your LNB has a\nwide beam, so you receive the signals from over a dozen different GEO\nsatellites. The signal you want to receive is now interfered by DVB-S\ntransponders (or other signals) from many different satellites and now\nyou have a problem (as before the main contribution of noise was the LNB\nnoise figure, and now you notice that the noise floor is much higher due\nto interference).\n\nThis is not a problem when using a dish, since the beamwidth is rather\nnarrow and your dish only sees a few satellites at a time, so\ninterference is unlikely. But when you look at many satellites instead,\nthe spectrum is extremely crowded.\n\nThe fun thing about this story is that they claim that the are\nexperimenting with LoRA to fight co-channel interference (since LoRA is\nspread spectrum). In my last talk about Outernet I commented that this\nis nonsense and that they don't understand properly how spread spectrum\nworks.\n\nIf you think about it, spread spectrum (in comparison to a narrowband\nsignal) works very well against narrowband interference, but it doesn't\nmake any difference against wideband interference. In this case, the\nco-channel interference is DVB-S and other wideband signals. For all\npractical effects, they just look as an elevated noise floor and there\nis no way to fight against them, spread spectrum or not.\n\n\nSince the Outernet topic has come to this mailing list once again, I\ntake the liberty to remind you that while Outernet can be interesting\nfrom the technical point of view, they have always kept secret their\nmodulation, coding, protocols and so on, and the key parts of the\nreceiver are closed-source. This is no good for Amateur Radio and\nexperimentation in general.\n\nThanks to my work and the help of some other people, now there is a\nfully open-source receiver for the (now defunct) L-band signal, as well\nas public specifications for everything. This was done by reverse\nengineering, without any support from the Outernet team (which don't\nseem to like this open-source receiver).\n\nSome references:\n\nhttps://github.com/daniestevez/free-outernet\n\nhttp://destevez.net/tag/outernet/\n\nhttp://destevez.net/talks/\n\n\n73,\n\nDani EA4GPZ.\n",
    "attachments": []
}