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{
    "url": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/email/JXR4XNGAJYG4R5ESUJPIDU6GMULODX2L/?format=api",
    "mailinglist": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/?format=api",
    "message_id": "[email protected]",
    "message_id_hash": "JXR4XNGAJYG4R5ESUJPIDU6GMULODX2L",
    "thread": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/thread/JXR4XNGAJYG4R5ESUJPIDU6GMULODX2L/?format=api",
    "sender": {
        "address": "john (a) papays.com",
        "mailman_id": "40c82fe75f644d01882ed3a91ae267dd",
        "emails": "https://mailman.amsat.org/hyperkitty/api/sender/40c82fe75f644d01882ed3a91ae267dd/emails/?format=api"
    },
    "sender_name": "John Papay",
    "subject": "[amsat-bb]  Doppler Correction?",
    "date": "2011-07-25T02:00:21Z",
    "parent": null,
    "children": [
        "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/email/6E6XCTNIJKEGFWBJOLL3L5YT7GMYNC2O/?format=api",
        "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/email/NJYZ2AROB5AHLHNE32KNDD6L6ETYPUXE/?format=api"
    ],
    "votes": {
        "likes": 0,
        "dislikes": 0,
        "status": "neutral"
    },
    "content": "The purpose of full doppler correction is to keep your signal in\nthe exact same spot on the receiver in the satellite.  It has a finite\npassband and if you don't correct your uplink, you move within that finite\npassband.  Theoretically a single linear transponder can support many\nconversations but it will not support the maximum unless everyone stays\nput at the satellite receiver.  Those who don't doppler correct slide \nwithin the\npassband and run into those who are staying put.  Of course if you adjust\nyour uplink so you stay put at the satellite, you have to adjust your\nreceiver to hear yourself because of the doppler shift in the other direction.\nBoth uplink and downlink require doppler correction in this case.\n\nIf you don't have a rig that can be computer controlled or if you are\noperating portable and can't readily incorporate a laptop into your\nsetup for whatever reason, then by all means manually adjust the highest\nfrequency since that is the one that changes three times faster than the\nlower frequency in a v/u satellite.  You simply do the best you can.\n\nHowever, if you have a home rig that can be computer controlled, then by all\nmeans use a computer to adjust your doppler.  Stay in one spot in the\nsatellite's passband.  You can make faster contacts since you only have\nto pick up the mic to talk or use the key to send cw.  If you are working\ndx and the window is short, being on frequency and staying put will help\nput that distant grid in the log.\n\nThe program does all the work but you must be sure that your keps\nare current AND your computer clock is accurate to the second.  On a\nhigh pass when the satellite is overhead, the doppler changes very fast\nand even a few seconds of clock inaccuracy will have you not hearing\nyourself in a normal voice.  At lower elevations the doppler is not as\nsevere so a few seconds won't make much difference.\n\nUse the HO-68 beacon to test your doppler correction.  Set your radio for\nCW with a 500 Hz or better bandwidth.  Pick a high pass where the bird will\nget up over 45 degrees.  Tune the beacon in at your AOS and then don't touch\nthe dial.  If the CW note stays constant over the entire pass, your system\nis operating perfectly.  Make sure your program settings are such that there\nare frequent frequency updates.  I have mine set at 1 second no matter what.\nSome older radios will not accept frequency changes while you are \ntransmitting.  In\nthat case, make sure you only key down for short periods of time so the\nradio frequency can be updated.\n\nOf course you must adjust your uplink calibration on SatPC32 so that you\nhear yourself on the downlink.  Hearing yourself in a normal voice will\nbe an indication that you have your calibration set properly.\n\nMost of the birds stay on frequency, but I've noticed that AO-7 Mode B will\nbe off by 1700Hz when it changes from Mode A to Mode B.  Normally we would\nnot observe this phenomenon but since lately we have had this mode change while\nover North America we are able to experience it.  Within a few minutes, the\nsatellite is down to a 1200 Hz offset.  I'm not sure what happens on the next\npass because it is out of my footprint.  The next morning, however, the bird\nis back to my normal setting.  This means the frequency drifts about 1700 Hz\nback down to it's steady state value.  The other birds may have some slight\ndrifting, probably due to spacecraft temperature but it is minimal, less than\na few hundred Hz.  So when you are trying to make a contact on the first\nAO-7 pass in Mode B, be prepared to readjust your uplink calibration so you can\nhear yourself.  It may be as much as 1700Hz at the start.\n\nIn my opinion, everyone that can control their radio for doppler should do so.\nDoppler correction gives us the maximum usage out of our linear transponders.\nWhy go through the agony of fiddling with your radio when your computer can\nmake your life so much easier.  You will never have to apologize for not being\non frequency.  If I wasn't able to have doppler control on my radio, I wouldn't\nspend much time on the linear birds, unless of course there was a rare grid\nto be worked. <grin>\n\n73,\nJohn K8YSE  \n\n",
    "attachments": []
}