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{
    "url": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/email/RQTXJQ4MSAGDRGTCWPHM4YTJLW4CWPUD/?format=api",
    "mailinglist": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/?format=api",
    "message_id": "[email protected]",
    "message_id_hash": "RQTXJQ4MSAGDRGTCWPHM4YTJLW4CWPUD",
    "thread": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/thread/RQTXJQ4MSAGDRGTCWPHM4YTJLW4CWPUD/?format=api",
    "sender": {
        "address": "rwmcgwier (a) comcast.net",
        "mailman_id": null,
        "emails": null
    },
    "sender_name": "Robert McGwier",
    "subject": "[eagle]  Please check these calculations",
    "date": "2006-11-01T04:27:40Z",
    "parent": null,
    "children": [
        "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/email/7JN5EWRNC5ESXU3RXOGMNHHZYN5SAE3H/?format=api"
    ],
    "votes": {
        "likes": 0,
        "dislikes": 0,
        "status": "neutral"
    },
    "content": "We have done all of these calculations for the links and published these \nspread sheets.  The spread sheets show the typical bias towards taking \nthermal noise and some \"guesstimate\" as to interference levels but not \nreally taking into account LO noise. \n\n\"Everybody\" can understand that noise performance in a mixer that has a \n50 ohm input port (which is hooked to a 50 ohm load) with the pretend \nnoise power density of -174 dBm/Hz (k T0).  The noise factor  of the \nmixer is taken into account  in the usual way\n\nNoise Factor = kT0 (F-1)  where k is Boltzman,  T0 is room temperature \nand F is the noise factor in the mixer.\n\nBut,  we have these oscillators that we say we want tunable.  I doubt we \nactually want them to be tunable but let's start to go through this so \nwe can calculate if I am right.\n\nReciprocal mixing is the crap that gets thrown into your receive pass \nband by a strong signal (strong compared to our weak SMS text signal for \nexample)  and raises the receiver noise floor.  We have these computed \nsignal strengths at the spacecraft and we do not want to raise the noise \nin our signal bandwidth by more than a few dB (none?)  ;-)\n\nLet's make some simplifying assumptions that the bottom end of the \npassband will be as empty as it has always been and the upper half band \nwill have the usual ten suspects in them and not much more.  The usual \n20 people using the linear transponder on the satellite.\n\nSo we will assume that we are out in the \"flat part\" of the LO noise and \nthat a signal of level  S is out there.\n\nOur bandwidth of our desired signal  (the undesigned SMS text message \nsigna for example)  is B and the LO noise floor is L.\n\nand we worry that\n\nRN (reciprocally mixed noise) =  S * L * B  will appear and hurt us to \nthe point of signal being covered and for example, SMS not working.\n\nSNR(in)/SNR(out)  =  F +  RN/(kT0 B)\n\nIf we wish to see signal level Text at our receiver then  we can \nestimate the noise floor required of the LO (L) to be (using the \nprevious formulae)\n\nL  = Text - S - C/I  - 10log10(B)\n\nwhere C/I is the carrier to interference ratio required at the output of \nthe mixer.   Notice that the reciprocal noise specification depends \ndirectly on the input blocking signal strength S.  So this is a bit more \ncomplex than one might think at first so some more thought needs to be \nput into this before we leap to say the 70 cm design is good, bad, or \nindifferent.\n\nWe need to resolve this in the next few days so John, Juan, and the rest \nof our receiver friends can have a design to build to.  Please \neveryone,  check over my formulae before I go and do a ton of work that \nis all wasted.  If you don't like the form of them,  suggest something \ndifferent.  I suggest we build a spread sheet that does these \ncalculations in a \"mutually coupled\" way.  I am off to Lyle's on \nThursday and will not be able to do much more on this before I return.  \nSomebody jump all over it please if you want to.\n\n\nBob\n\n\n\n-- \nAMSAT Director and VP Engineering. Member: ARRL, AMSAT-DL,\nTAPR, Packrats, NJQRP, QRP ARCI, QCWA, FRC. ARRL SDR WG Chair\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": []
}