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{
    "url": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/email/CFEJG7NHLSOAEHEKLBU4KYWCEKKVCEPI/",
    "mailinglist": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/",
    "message_id": "002701c869cc$d2f07d00$6401a8c0@Sony2G4",
    "message_id_hash": "CFEJG7NHLSOAEHEKLBU4KYWCEKKVCEPI",
    "thread": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/thread/FVVMU6KDIBRYIBRJKDVHIPGOYYDN3T5M/",
    "sender": {
        "address": "n5gui (a) cox.net",
        "mailman_id": null,
        "emails": null
    },
    "sender_name": "James Whitfield",
    "subject": "[amsat-bb] Re: Automatic doppler tracking of DSB",
    "date": "2008-02-07T21:03:00Z",
    "parent": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/email/HXC2JOJDEIOEA6XXHGNYJCJK54VZPIFN/",
    "children": [],
    "votes": {
        "likes": 0,
        "dislikes": 0,
        "status": "neutral"
    },
    "content": "Success!!!!\n\nWell at least sort of.  I received an informative message from PE4WJ, Wouter\nJan Ubbels, who is part of the team working on Delfi-C3, which is scheduled\nto launch in April.  As part of that project he has made available a sound\ncard based program, called Warbler, to demodulate the 1200 baud telemetry\ndownlink.  It uses a Costas Loop to demodulate and for Doppler correction.\nHe suggests that the program could be expanded, or at least adapted for\nvoice DSB signals.  While he is busy with Delfi-C3, he seems interested in\nour discussions.  Perhaps we can come up with some ideas that are worth\ntrying to add to future versions of Warbler.\n\nI had originally thought that the idea should have been considered before,\nand I am pleased to know that it is actually in use.  The fact that it is in\nuse by the digital \"community\" but I could not seem to find any reference to\nit, is a yet another example of a communications problem that has spanned my\nthree decade engineering career: different technical fields have such\nspecialized languages that the members of each cannot recognize when they\nare talking about similar things.  I should have recognized that I needed\nbetter understanding of just why AO-16 has a DSB transmitter.   It makes a\nlot more sense after I read an article by G3RUH called \"the shape of bits to\ncome\" which Wouter suggested.  I still have a lot to learn, but I am\nstarting to comprehend the following quote from the article:\n\n         Binary data DSB modulating an RF carrier\" and \"binary phase shift\nkeying (BPSK)\" are exactly the same thing.\n\nWhat I might add to try to clarify the statement for those, like me, for\nwhom it was not immediately obvious is that \"Binary Data\" in this context\ncomes in the form of +1 and -1 instead of 1 and 0 .  For some of us it makes\nthe difference between BPSK and OOK.\n\nIf I am understanding Warbler, it brings in the 1200 baud BPSK, which\n\"looks\" like DSB with 2400 Hz bandwidth, into a sound card.  The signal is\ntuned so that the \"carrier\" would be between 1400 and 1800 Hz.  Once the\nCostas Loop is locked, it will then compensate for 400 Hz of Doppler shift.\nIf the \"carrier\" drops below 1400 or above 1800, the extremes of DSB signal\nwould get attenuated by the passband of an SSB receiver, which is assumed to\nbe used to pick up the signals from satellite.\n\nModifications for voice DSB, would start by the use of a wider receiver,\nperhaps an AM mode instead of SSB.  Assume for the moment that we have a\nreceiver audio bandwidth of 10 KHz.  If the audio used to modulate the DSB\ntransmitter is limited to 3 KHz, then the DSB signal will be 6 KHz.  Set the\nCostas Loop to track \"carrier\" from 3.3 KHz to 7.0 KHz then you get a 3700\nHz Doppler correction range.  The sound card would then process the upper\nand lower sidebands into the original speech which would then be produced by\nthe sound card.  You could whittle that down some by communication quality\naudio trimmed to 2.7 or even 2.5 KHz.  The Doppler range increases to 4300\nand 4700 Hz.  A wider receiver band would also be a benefit, limited by the\nhigh frequency limit of the sound card.  And of course a wider receiver lets\nin more noise.  The additional noise suggests digital processing.\n\nWouter also suggested that software defined radio could be used instead of\nthe scheme outlined above.  SDR is the concept that I had in mind.  Perhaps\na simple system that has the I and Q channels fed into the L and R sound\ncard inputs, Costas Loop and additonal processing in the computer, sound\ncard or serial output to control the VCO.  The bandwidth would be limited by\nthe sound card audio inputs, but the Doppler tracking correction would then\nbe limited only by the range of the VCO and its update rate.\n\nI think this is worth the time to experiment.  The situation with AO-16\ncertainly makes it easy to get voice DSB signals on the downlink.  One only\nneeds FM transmissions.  It could be used on a translating repeater, but I\nwould suggest that it would be courtesy to not try it on a crowded area.  If\nDSB gets a bad reputation for \"hogging\" limited bandwidth, it will never get\nfair consideration for current or future satellites.  DSB does not use as\nmuch spectrum as FM, and I hope that it can demonstrate a benefit for\nDoppler compensation.  It has yet to prove its value the amateur satellite\ncommunity.  I think it will be fun to try.\n\nI certainly hope that I have presented some ideas that encourage thinking,\nlearning, and experimentation.\n\nBest Wishes.\n\nJames\n n5gui\n\n\n\n\n\n\n\n",
    "attachments": []
}