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{
    "url": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/email/JPQQ67KYYI67YXFALIYSUQQ7JQCBODW2/?format=api",
    "mailinglist": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/?format=api",
    "message_id": "[email protected]",
    "message_id_hash": "JPQQ67KYYI67YXFALIYSUQQ7JQCBODW2",
    "thread": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/thread/XJQD5OAWRSPADLXM2OPYVVKCWMP7IYYY/?format=api",
    "sender": {
        "address": "nx7u (a) arrl.net",
        "mailman_id": null,
        "emails": null
    },
    "sender_name": "Scott Townley",
    "subject": "[amsat-bb] Re: Making progress",
    "date": "2007-08-08T03:22:12Z",
    "parent": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/email/OJPE6KIVYCOLACLUDPPLQZGB246NG6JR/?format=api",
    "children": [],
    "votes": {
        "likes": 0,
        "dislikes": 0,
        "status": "neutral"
    },
    "content": "Scott,\nYou point out an interesting difference between HF and UHF...\n\n<quoted> The preamp was a concern for me in that since I've been working \nHF, I've\nfound that I receive much clearer with the preamp disabled and the\nattenuator enabled and just pushing up the AF gain. I realize this is\ndue to noise in the area and the fact that the IC-7000 preamp is a\nbroadband preamp, and generally will just increase the noise floor and\nlower the sensitivity of the frequencies I'm actually interested in. <end \nquoted>\n\nThe main difference is the noise of the exterior environment.  Without \ngoing into the gory mathematical details, essentially the noise figure of \nthe exterior environment is on the order of 40-60dB on 40m, decreasing to \nroughly 5-10dB on 10m.  Most radios have RX noise figures on the order of \n~10dB.  Basically the radio only needs to be a bit more sensitive than the \nexternal environment--which is why attenuators are more appropriate for \n40m, and sometimes (but not always) a preamp becomes helpful up on 10m.\n\nAt 70cm the external noise is on the order of a couple of dB...but the coax \nand radio push the total up to ~12dB...so a low-noise amplifier at the \nantenna can make a LOT of difference.  I once made a calibrated off-air \nmeasurement of the sensitivity improvement rendered by an ARR GaAsFET \npreamp on an M2 eggbeater (another omni antenna) and found 8-10dB improvement.\n\n\n\nScott Townley NX7U\nGilbert, AZ  DM43di\nhttp://members.cox.net/nx7u \n\n\n",
    "attachments": []
}