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{
    "url": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/email/7MXPEUHOJZHZALUIYF2FV6BFYPU4D5ZC/?format=api",
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    "message_id": "[email protected]",
    "message_id_hash": "7MXPEUHOJZHZALUIYF2FV6BFYPU4D5ZC",
    "thread": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/thread/W7YSOEWVIM5GDIASTAAFDTKT56OUSA2N/?format=api",
    "sender": {
        "address": "daniel (a) destevez.net",
        "mailman_id": "c2eac82b839b45f5a7d3b923c1721007",
        "emails": "https://mailman.amsat.org/hyperkitty/api/sender/c2eac82b839b45f5a7d3b923c1721007/emails/?format=api"
    },
    "sender_name": "Dani EA4GPZ",
    "subject": "Re: [amsat-bb] RX-only Antenna \"tee\" connector?",
    "date": "2017-01-11T14:46:53Z",
    "parent": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/email/W7YSOEWVIM5GDIASTAAFDTKT56OUSA2N/?format=api",
    "children": [],
    "votes": {
        "likes": 0,
        "dislikes": 0,
        "status": "neutral"
    },
    "content": "El 11/01/17 a las 02:11, Scott escribió:\n> Hi everyone.\n> \n> I suppose that any deviation from the ideal setup of a near-perfectly\n> matched antenna & receiver will have SOME negative effect, but for a\n> receive-only antenna, how badly am I hurting myself to split the\n> antenna between two receivers?\n> \n> Since frequency is probably important to answer this, I’m referring\n> to 70cm.\n> \n> Also, if it matters, I have a very good preamp (SP-70 from SSB) at\n> the antenna feeding 25 meters of LMR-400.  Both receivers are SDR\n> devices (receive-only).\n\nHi Scott,\n\nA perfect splitter introduces a loss of 3dB, since half of the signal\ngoes to the other receiver. A real world splitter will have a slightly\ngreater loss due to imperfections, but something like 3.1dB or 3.2dB is\nusual, so I'll call that 3dB for the sake of the argument.\n\nIf you have no preamp, this raises your noise figure by 3dB. However,\nsince you have a preamp before the splitter, you have to divide by the\ngain of the preamp. Say your preamp has a gain of 20dB (which is\ntypical). Then your noise figure is only raised by 0.03dB, which is tiny.\n\nThe important question is how much signal-to-noise you lose because of\nthis increase of 0.03dB in noise figure. This depends on your antenna\ntemperature (which is the amount of noise that your antenna grabs from\nthe environment). Noise figure is normalized at 290K, so if your antenna\ntemperature is 290K you lose precisely 0.03dB of SNR. Your antenna\ntemperature is almost never 290K. At 2m it is likely that the antenna\ntemperature will be much greater than 290K, on the order of thousands of\nK. Therefore, your losses in SNR are much smaller than 0.03dB. On 70cm\nand higher, the antenna temperature can be lower than 290K (much lower\non the high microwave bands), especially in quiet rural zones.\nTherefore, your SNR losses will be much greater than 0.03dB but still a\nfraction of a dB, so you won't even notice the losses.\n\nThese are the exact calculations (by the way, the same calculations can\nbe used for coax losses and any other sort of losses after the preamp).\nIn layman's term it's much simpler: you lose (almost) nothing, because\nyour preamp provides enough signal gain to feed both of your receivers\nwith adequate signal level, despite the fact that the signal power is\nsplit in half.\n\nThere might be a problem if the gain of your preamp is especially low\n(say 10dB) and you're in a very quiet area.\n\n73,\n\nDani.\n\n",
    "attachments": []
}