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{
    "url": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/email/FDYULSALZFNEMOGSG4Q65VSSAZLLCPGY/?format=api",
    "mailinglist": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/?format=api",
    "message_id": "[email protected]",
    "message_id_hash": "FDYULSALZFNEMOGSG4Q65VSSAZLLCPGY",
    "thread": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/thread/ZEDJYNGRAQTKYFUU3RZB3MTHWTZOGVLJ/?format=api",
    "sender": {
        "address": "minyard (a) acm.org",
        "mailman_id": "59a713764a2e4ccabdcfd85f5b213a94",
        "emails": "https://mailman.amsat.org/hyperkitty/api/sender/59a713764a2e4ccabdcfd85f5b213a94/emails/?format=api"
    },
    "sender_name": "Corey Minyard",
    "subject": "[pacsat] Re: Modulation options",
    "date": "2022-10-07T01:50:22Z",
    "parent": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/email/NO3R3NMEP6JXKCTKCCC76V32L6ZR74FV/?format=api",
    "children": [
        "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/email/S3KUHB5YMDGL4SNACIWXIL3NZ5WA2FNG/?format=api"
    ],
    "votes": {
        "likes": 0,
        "dislikes": 0,
        "status": "neutral"
    },
    "content": "On Tue, Sep 27, 2022 at 04:12:42PM -0400, Rich Gopstein wrote:\n> Corey brings up a good point - what are we trying to accomplish with this\n> board?  I might have missed some early discussions about the goal, so\n> forgive me if this has been discussed already.\n\nYes, it would be nice to have \"Commander's Intent\" on this.  It helps\nknow what to do.\n\n-corey\n\n> \n> Are we trying to solve pacsat only,  or are we looking to design a more\n> flexible board that might be able to do more than just the pacsat\n> protocol?  Is there an advantage to sticking with known off-the-shelf RF\n> parts (i.e. the AX5043), or should we consider doing something more SDR-ish.\n> \n> That might help us decide if the TMS570 is the \"right\" processor to get.\n> \n> Rich\n> \n> On 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> pacsat mailing list -- [email protected]\n> View archives of this mailing list at 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 https://mailman.amsat.org\n\n",
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