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{
    "url": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/email/ZVG3UWHXLCH2AYRXAL5ZZAM7W3OEP2KP/?format=api",
    "mailinglist": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/?format=api",
    "message_id": "[email protected]",
    "message_id_hash": "ZVG3UWHXLCH2AYRXAL5ZZAM7W3OEP2KP",
    "thread": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/thread/YVFJXOA5COUXOIUAVSTGR3EKXJ2C7STS/?format=api",
    "sender": {
        "address": "k6vug (a) sbcglobal.net",
        "mailman_id": "37fd9aee884c4835a5c51104b6295d3a",
        "emails": "https://mailman.amsat.org/hyperkitty/api/sender/37fd9aee884c4835a5c51104b6295d3a/emails/?format=api"
    },
    "sender_name": "[email protected]",
    "subject": "Re: [amsat-bb] Doppler shift question",
    "date": "2019-06-05T18:31:18Z",
    "parent": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/email/YVFJXOA5COUXOIUAVSTGR3EKXJ2C7STS/?format=api",
    "children": [
        "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/email/LSSUOSWOCEWBILQYF4DHU2N7ZSYV3OBK/?format=api"
    ],
    "votes": {
        "likes": 0,
        "dislikes": 0,
        "status": "neutral"
    },
    "content": " Let me take a stab at this... \n \nThe obvious thing about doppler is that, as the sat comes at you the frequency sounds higher than  its normal frequency and lower when it goes away from you. Hence we set our receivers at a slightly \"higher\"  frequency at AOS and step lower until LOS. \n \nThe not-so-obvious thing is that a similar effect happens \"at the satellite\", so if we transmit at the normal frequency, it will appear slightly higher at the satellite, as it comes at you. Since the satellite receiver cannot change, we compensate by transmitting at a slightly lower frequency so it is \"normal at the satellite\" and we keep stepping it up until LOS. \n The amazing/confusing thing about space is that everything is relative, i.e., the sat and the earth station are just moving relative to each other. \n \nHope that helps ! \n \n73! \nUmesh \nk6vug \n \n\n\n\n\n\n\n    On Wednesday, June 5, 2019, 10:45:46 AM PDT, Philip Jenkins via AMSAT-BB <[email protected]> wrote:  \n \n This came up at AMSAT Academy at Hamvention, and I still can't wrap my head\naround it (something simple I'm not getting, I'm sure). I know the\nxmit/receive frequencies aren't shifted, stay the same at the satellite.\n\nSO-50 has a 435 Mhz downlink; as the satellite approaches me from AOS I\nlower my receive frequency (and continue lowering it as the bird approaches\nLOS). So far so good.\n\nAO 91/92 have a 435 Mhz uplink,; as the satellite approaches me from AOS, I\ngo up in my transmit frequency.\n\nHere is where I get lost: Why do I* lower* the frequency on 435 Mhz when\nreceiving a satellite, but *raise* the 435 Mhz frequency when transmitting\nto a satelllite?\n\nSo, my question boils down to - why should transmit doppler shift go in the\nopposite direction from receive on the same band? In both cases, the\nsatellites are approaching me (from AOS).\n\nBasically, why the difference when I'm transmitting  and when I'm\nreceiving?\n\n73\n\nPhilip N4HF\n_______________________________________________\nSent via [email protected]. AMSAT-NA makes this open forum available\nto all interested persons worldwide without requiring membership. Opinions expressed\nare solely those of the author, and do not reflect the official views of AMSAT-NA.\nNot an AMSAT-NA member? Join now to support the amateur satellite program!\nSubscription settings: https://www.amsat.org/mailman/listinfo/amsat-bb\n  \n",
    "attachments": []
}