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{
    "url": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/email/XYSIVNE3EPI3V2XKY7VZSRG53SSI6SFU/?format=api",
    "mailinglist": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/?format=api",
    "message_id": "000a01c71e86$082d0e90$ccbfb546@kc6uqh",
    "message_id_hash": "XYSIVNE3EPI3V2XKY7VZSRG53SSI6SFU",
    "thread": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/thread/PPXDQMVNMMNPWL2JRDLSXLWBNPOTCWRM/?format=api",
    "sender": {
        "address": "kc6uqh (a) cox.net",
        "mailman_id": "d9201820d18047e4a2772c86bda5e111",
        "emails": "https://mailman.amsat.org/hyperkitty/api/sender/d9201820d18047e4a2772c86bda5e111/emails/?format=api"
    },
    "sender_name": "kc6uqh",
    "subject": "[amsat-bb] Re: Pre amp question",
    "date": "2006-12-13T07:12:21Z",
    "parent": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/email/WU4IZNSCXFYOTLLHOT6UDEQSHCFUKF6N/?format=api",
    "children": [],
    "votes": {
        "likes": 0,
        "dislikes": 0,
        "status": "neutral"
    },
    "content": "Steve,\n\nThe preamp is working fine. The earth is at 290 degrees Kelvin. Unless the \nantenna sees only cold sky and no earth, trees & buildings you will have 3dB \nof noise going into your preamp. If your radio has a 1 dB noise figure and \nyour preamp has a 1 dB noise figure no improvement of S/N is noticed only \nthe level has changed by the gain of the preamp. Preamps only help to cover \ncable loss and poor receiver sensitivity. Low noise figures ( less than 3 \ndB) are only achieved when the antenna is pointed into space and has a good \nfront to back ratio.\nFrequencies below 70 cm are subject to galaixy noise that becomes larger as \nfrequency goes lower. expect a 3-4 dB increase at 2M, no noise reduction \nfrom cold sky @ 2 M and longer wave lengths.\n\nArt, KC6UQH\n\n----- Original Message ----- \nFrom: \"Edward R. Cole\" <[email protected]>\nTo: \"Steve Raas\" <[email protected]>; <[email protected]>\nSent: Tuesday, December 12, 2006 9:37 PM\nSubject: [amsat-bb] Re: Pre amp question\n\n\n> At 09:30 PM 12/12/2006 -0500, Steve Raas wrote:\n>>\n>>As I prepare for getting on the birds.. I decided to test out this AG-25\n>>preamp that came with my new radio. Now my experience with preamps is\n>>limited, but this one is rather baffling me.\n>>\n>>I connected everything in line.. and powered up the preamp and at 1st \n>>glance\n>>it appeared that it worked fine, however after about 10 seconds I started\n>>questioning a few things.\n>>\n>>#1 My noise floor went up 10db ( I've never seen this before I guess my\n>>experience with preamps is just the good ones )\n>>\n>>#2 My Received signal quality was unchanged all it did was make the signal\n>>'appear' stronger on the meter.\n>>\n>>Now I know if the preamp was dead.. I would hear nothing.. so I am going \n>>to\n>>go out on a limb here and assume that its either:\n>>\n>>a)       an incredibly broad band pre-amp with a completely fictitious ' \n>>Low\n>>noise floor ' claim or\n>>\n>>b)       Detuned\n>>\n>> I guess what Im going after is a few things with this email .. has any \n>> one\n>>ever taken one of these AG-25's and given it a proper tuning? Or is this\n>>what I should expect with this particular item?\n>>\n>>In my previous experience (terrestrial weak sig stuff) a decent preamp may\n>>up the noise floor from a s-meter reading of mabey 0 or 1 to a s5, but \n>>with\n>>a significant increase in received signal gain. and intelligibility.\n>\n> Steve,\n>\n> My guess is that the stock ICOM preamp is not especially low-noise.\n> Typically, they are more like 1.5 to 3 dB NF and that would give the\n> results you see...more gain but little quieting.\n>\n> Years ago I ran a nuvistor preamp (3-dB NF with 15-dB gain) and all it\n> mainly did was add gain (made signals louder including the noise).\n>\n> Now if you have the preamp installed in the shack next to the radio with\n> lots of coax up to the antenna, you will get less low-noise performance\n> (even if it is a good low noise amplifier).\n>\n> Finally, have you checked receiving weak signals?  Testing with strong\n> signals will not show much difference other than higher s-meter reading.\n> 73's,\n> Ed - KL7UW\n> =========================================\n> BP40iq,  Nikiski, AK      http://www.qsl.net/al7eb\n> Amsat #3212\n> Modes: V - U - L - S\n> USA Rep. for Dubus Magazine: [email protected]\n> =========================================\n>\n> _______________________________________________\n> Sent via [email protected]. Opinions expressed are those of the author.\n> Not an AMSAT-NA member? Join now to support the amateur satellite program!\n> Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb\n> \n\n\n",
    "attachments": []
}