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{
    "url": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/email/IYBS4KXJ4KFL43NRMAWWIKLKOXLAGSI4/?format=api",
    "mailinglist": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/?format=api",
    "message_id": "[email protected]",
    "message_id_hash": "IYBS4KXJ4KFL43NRMAWWIKLKOXLAGSI4",
    "thread": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/thread/IYBS4KXJ4KFL43NRMAWWIKLKOXLAGSI4/?format=api",
    "sender": {
        "address": "hans.bx2abt (a) msa.hinet.net",
        "mailman_id": null,
        "emails": null
    },
    "sender_name": "Hans BX2ABT",
    "subject": "[amsat-bb] AirSpy & LNA questions",
    "date": "2018-07-13T14:29:20Z",
    "parent": null,
    "children": [
        "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/email/RQWA7EOLFQBR3JTBRO2QX2HRZMY5Z5HT/?format=api"
    ],
    "votes": {
        "likes": 0,
        "dislikes": 0,
        "status": "neutral"
    },
    "content": "Man, this sat stuff is difficult and I was getting a bit frustrated with \nlack of progress, to be honest. But just when I thought I didn't get \nanywhere, I went a big leap forward. But I'm not there yet, so I need \nyour input.\n\nMy goal is to get some decent reception of the major telemetry sats, \ne.g. Funcube-1. I have two rigs: an ICOM IC820H and an AirSpy Mini SDR \nrunning on a Linux box with GQRX as front-end. I have a Chinese Arrow \nAlaska clone pointing 200 degrees with 20 degree elevation. The other \nantenna currently is a turnstile tuned for 137 MHz, but I have 2/70 DCAs \nas well (they had to come down this week because of a typhoon. Will be \nup again shortly).\n\nThe bare antennas do fine on terrestrial signals, but up till now very \nfew sats were heard (mostly the Xiwang sats and Athenoxat-1) and signals \nwere very very weak. I got myself some proto boards and PGA103+ MMICs \nand built two LNAs according to schematics found on the web. On the \nworkbench they perform as they should and give some 15-25 dB gain \ndepending on what frequency is used. I use an old AM/FM signal generator \nand an RTL-SDR as crude scope since I don't have a real one.\n\nI mounted the LNAs as close as possible to the antennas and they are fed \nwith a bias-T from Minikits.com.au. The first results were \ndisappointing: I used the AirSpy and noticed a lot more signal but also \nan increased noise floor. With the AirSpy there is a lot of fiddling \ngoing on in the software and I managed to get some improvement by \ntweaking the LNA gain, Mix gain and IF gain. Still I couldn't hear any \nsat signals.\n\nThis afternoon I switched from the AirSpy to the IC820H and \nlo-and-behold very strong beacon signals from XW2A and F; the strongest \nI've ever heard. Even the AirSpy did detect a signal, although \nnot-at-all as great as the IC820H. To get a cleaner signal from the \nIC820H I did have to engage the attenuator on the set, though. Using the \nIC820H I also heard a very weak beacon signal from CO-65, but the AirSpy \nfailed there. Conclusion: the IC820H could detect signals that the \nAirSpy could not detect at all or detect them much better.\n\nPretty happy with this step forward, but not satisfied. Question is how \nto improve even more.\n\nQ1: is the LNA desensing the AirSpy (and to a lesses extend, the IC820H) \nand if so, how to fix that? I read something about an attenuation \nnetwork after the LNA to improve the front-end of the receiver. Might \nthat help?\n\nQ2: when not powered, MMICs seem to have a very high insertion loss. Is \nthere a way to remotely bypass the LNA in order to compare reception \nwith and without the LNA?\n\nQ3: would filtering help? E.g. bandpass filters for 2m and 70cm. I do \nrealize that this would mean another couple of dB of insertion loss, but \nmaybe that disadvantage outweighs the advantages.\n\nI would appreciate any input on the above and also would like to hear \nfrom others who use the AirSpy Mini for sat reception. I already did a \nlot of googling, but can't find any clear cut answers. Hope you all can \nhelp me go into the right direction. Cheers,\n\nHans\nBX2ABT\n\n",
    "attachments": []
}