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{
    "url": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/email/2FX43IHLKU4A7LAGRIGYXJAKU6FOZMKM/?format=api",
    "mailinglist": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/?format=api",
    "message_id": "[email protected]",
    "message_id_hash": "2FX43IHLKU4A7LAGRIGYXJAKU6FOZMKM",
    "thread": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/thread/KMX7JNE3JKZQIQQLXOACJNQH2GA7TPG3/?format=api",
    "sender": {
        "address": "rwmcgwier (a) comcast.net",
        "mailman_id": null,
        "emails": null
    },
    "sender_name": "Robert McGwier",
    "subject": "[eagle] Re: Proposed Eagle Antenna Arrays",
    "date": "2006-09-27T19:19:36Z",
    "parent": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/email/6E2SPEXTUXTVZNESTON4KNM2ADR7HV2R/?format=api",
    "children": [
        "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/email/3PYMYB74XEYTLZYHILPSWCJJD6YU5XI2/?format=api"
    ],
    "votes": {
        "likes": 0,
        "dislikes": 0,
        "status": "neutral"
    },
    "content": "Tom Clark, K3IO wrote:\n> Louis McFadin wrote:\n>> Unfortunately there is any way to put the antennas on the center of \n>> the spacecraft. There may be some spin modulation no matter what we do. \n>>\n>> On Sep 27, 2006, at 1:41 PM, John B. Stephensen wrote:\n>>\n>>> The designer of the code to demodulate class 1 uplinks in the \n>>> SDX needs to determine whether spin modulation can be compensated \n>>> for. The carrier tracking loop bandwidth may be close enough to the \n>>> satellite spin rate that it can't be eliminated. I'm not sure how \n>>> well open loop compensation would work as the phase pertubation will \n>>> vary with the arrival angle of the signal and this could vary by as \n>>> much as 30 degrees at MA32 and MA224.\n>>>  \n> Not quite true. For the phased arrays, if the required element phases \n> are computed relative to the spin axis, then spin-induced Doppler is \n> removed. You will get the spin Doppler only if you set the phase \n> reference to be the center of the patch array.\nBut the discussion here is not about the Microwave phased arrays.  Given \nthe rate at which we are signaling and the demodulator requirements that \nwill entail,  the spin modulation is a minor factor on the ACP.  For the \nvery low bit rate SMS text messaging,  and the 70cm uplink,  where we \nwere planning absolutely no phasing whatsoever,  it becomes a major \nfactor and might even be a deal killer without greatly increased \ncomplexity in the 70cm and 2m system.  Essentially,  you would have to \ncompute and predict a phase offset from the (say) 70 cm patch and apply \nthe correct again before we HELAPS or while we HELAPS on 2m, given \ninformation from the phased array for other bands and multiply each \nsample by the time varying phasor correction in the SDX to compensate.  \nI had not even considered doing this.  We need to cost HELAPS and STELLA \nbefore we know if this is achievable since I do not think we should \nincrease the power consumed by the DSP by increasing the clock or adding \nother computational elements.  But I do believe if it is achievable \ncomputationally,  and we can \"close the loop\" with parametric \ndetermination of the correction in band or from the other communications \npackage,  we can essentially eliminate the phase offset from the spin axis.\n>\n> One way this can be done is for some LO  (common to all the elements \n> of the phased array) needs to phase modulated with a rate equal to the \n> spin rate and with a magnitude/phase calculated on the basis of the \n> s/c-to-earth geometry. The only residual modulation to be compensated \n> in the PLLs is then determined by the offset of the OBSERVER from the \n> center of the earth.\n>\n> Last nite I think I convinced Bob that the added S2 interferometric \n> antennas (working against individual S2 array elements) will be able \n> to determine the spin axis orientation (and rate) w.r.t. the line(s) \n> connecting the s/c to dedicated terrestrial beacon(s) with accuracies \n> ~1º or better.\n\nI compute it is actually < 1°\n>\n> 73, Tom\n> ------------------------------------------------------------------------\n>\n> _______________________________________________\n> Via the Eagle mailing list courtesy of AMSAT-NA\n> [email protected]\n> http://amsat.org/mailman/listinfo/eagle\n>   \n\n\n-- \nAMSAT VP Engineering. Member: ARRL, AMSAT-DL, TAPR, Packrats,\nNJQRP/AMQRP, QRP ARCI, QCWA, FRC. ARRL SDR Wrk Grp Chairman\n\"You see, wire telegraph is a kind of a very, very long cat.\nYou pull his tail in New York and his head is meowing in Los\nAngeles. Do you understand this? And radio operates exactly\nthe same way: you send signals here, they receive them there.\nThe only difference is that there is no cat.\" - Einstein\n\n",
    "attachments": []
}