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    "url": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/email/NO3R3NMEP6JXKCTKCCC76V32L6ZR74FV/?format=api",
    "mailinglist": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/?format=api",
    "message_id": "CANsNeapYDSYoMT8ghtufz+cuWhp7zLhk2oPTmM6QrnJVte9Onw@mail.gmail.com",
    "message_id_hash": "NO3R3NMEP6JXKCTKCCC76V32L6ZR74FV",
    "thread": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/thread/ZEDJYNGRAQTKYFUU3RZB3MTHWTZOGVLJ/?format=api",
    "sender": {
        "address": "rich (a) ourowndomain.com",
        "mailman_id": "de4e965f89da4d4790638af3cb47f33c",
        "emails": "https://mailman.amsat.org/hyperkitty/api/sender/de4e965f89da4d4790638af3cb47f33c/emails/?format=api"
    },
    "sender_name": "Rich Gopstein",
    "subject": "[pacsat] Re: Modulation options",
    "date": "2022-09-27T20:12:42Z",
    "parent": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/email/LYHEIF66TYYBWMA66AZ6KOUQUH4JQ7XO/?format=api",
    "children": [
        "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/email/FDYULSALZFNEMOGSG4Q65VSSAZLLCPGY/?format=api"
    ],
    "votes": {
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    "content": "Corey brings up a good point - what are we trying to accomplish with this\nboard?  I might have missed some early discussions about the goal, so\nforgive me if this has been discussed already.\n\nAre we trying to solve pacsat only,  or are we looking to design a more\nflexible board that might be able to do more than just the pacsat\nprotocol?  Is there an advantage to sticking with known off-the-shelf RF\nparts (i.e. the AX5043), or should we consider doing something more SDR-ish.\n\nThat might help us decide if the TMS570 is the \"right\" processor to get.\n\nRich\n\nOn Tue, Sep 27, 2022 at 3:42 PM Corey Minyard <[email protected]> wrote:\n\n> On Tue, Sep 27, 2022 at 10:03:27AM -0500, Bill Reed wrote:\n> > I agree that Direwolf is probably a better performer.  Can we get an\n> audio\n> > stream out of an AX5043?\n>\n> It's not so much that we use direwolf, which we can't do.  It's if we\n> are going to consider other options.\n>\n> It sounds like, from Burn's description, that the AX5043 does FM\n> demodulation then AFSK (and I assume HDLC).  The packets from AFSK are\n> then sent to the main processor where unscrambling (is this used to\n> pseudo-ramdomize the data, or whiten it?) and FEC is done.  That's not\n> standard, as he said.\n>\n> The FEC is going to go a long way to improving the performance.\n> You could still do better with OFDM, but the current design is probably\n> good enough.\n>\n> -corey\n>\n> >\n> > On 9/23/2022 2:06 PM, Corey Minyard wrote:\n> > > I looked a bit last night at the ax5043; I didn't realize (I should\n> have\n> > > remembered) that it doesn't just convert to baseband, it actually\n> > > demodulates the signal.  Are current designs just using that for FM\n> > > demodulation and doing the AFSK modem in the TMS570?  I don't see a way\n> > > it could do both.\n> > >\n> > > It does appear to do GMSK.  The only concern there is if it can support\n> > > the polynomial used by G3RUH for randomization, I think.  I'd be\n> > > surprised if it didn't.  But I don't have the programmer's guide.\n> > > And it doesn't matter, I guess, if it can't do FM and GMSK at the same\n> > > time.\n> > >\n> > > For AFSK, you can do a lot better than what a hardware decoder can do.\n> > > See\n> https://github.com/wb2osz/direwolf/blob/master/doc/A-Better-APRS-Packet-Demodulator-Part-1-1200-baud.pdf\n> > > for details.  direwolf can pull signals out of the noise in a way that\n> a\n> > > hardware decoder can't.  The difference is significant.  I've done some\n> > > thing in my modem that can improve things even more.\n> > >\n> > > There is a similar situation for 9600:\n> > >\n> https://github.com/wb2osz/direwolf/blob/master/doc/A-Better-APRS-Packet-Demodulator-Part-2-9600-baud.pdf\n> > > But that's only the receive side, since this would only be transmitting\n> > > it doesn't matter.\n> > >\n> > > You could probably do the AFSK demodulation on a TMS570.  Modulation of\n> > > 9600 can probably be table driven, so that should be doable.\n> > >\n> > > Note that there are far better modulation techniques than these.\n> Almost\n> > > anything being done now is using OFDM of some type.  VARA is taking\n> over\n> > > in the packet world.  All modern modulation for cell phones is OFDM.  I\n> > > think digital TV is, too.  OFDM is certainly better for fading and\n> > > multipath and since it's using low-baud subcarriers I'd guess it's\n> > > better for doppler, too, but that's just a guess.  It would affect the\n> > > orthogonality (?) of the subcarriers though.  Not sure.\n> > >\n> > > You probably couldn't do OFDM on the TMS570.  Certainly not 4 channels.\n> > > You would probably need one of the TI chips that has a separate DSP.\n> > >\n> > > On the ground side, anyone with a sound card modem and a reasonably\n> > > modern PC could handle it.  It would provide better performance, I'd\n> > > guess singificantly better, than using AFSK and G3RUH.  (It would be\n> > > even better if you could get rid of putting it inside an FM carrier and\n> > > directly modulate, but that's probably not a practical option.)\n> > >\n> > > Also, on the satellite, if you converted to I and Q directly from RF,\n> > > and you had a DSP or a fast enough processor, you could get rid of the\n> > > AX5043s and do the FM and modem in the DSP.  I remember seeing single\n> > > chips that could do this, but I would have to hunt to find them.\n> > >\n> > > Anyway, since we are just getting started, I wanted to point out that\n> > > options are available that are better from a pure technical point of\n> > > view than what is currently being proposed.  I know there are other\n> > > concerns like the availability of current working circuits, power\n> budget,\n> > > timeframe, etc.\n> > >\n> > > -corey - AE5KM\n> > > -----------------------------------------------\n> > > pacsat mailing list -- [email protected]\n> > > View archives of this mailing list at\n> https://mailman.amsat.org/hyperkitty/list/[email protected]\n> > > To unsubscribe send an email to [email protected]\n> > > Manage all of your AMSAT-NA mailing list preferences at\n> https://mailman.amsat.org\n> > -----------------------------------------------\n> > pacsat mailing list -- [email protected]\n> > View archives of this mailing list at\n> https://mailman.amsat.org/hyperkitty/list/[email protected]\n> > To unsubscribe send an email to [email protected]\n> > Manage all of your AMSAT-NA mailing list preferences at\n> https://mailman.amsat.org\n> -----------------------------------------------\n> pacsat mailing list -- [email protected]\n> View archives of this mailing list at\n> https://mailman.amsat.org/hyperkitty/list/[email protected]\n> To unsubscribe send an email to [email protected]\n> Manage all of your AMSAT-NA mailing list preferences at\n> https://mailman.amsat.org\n>\n\n\n",
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