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{
    "url": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/email/Q2TRKWKDVYCKCAD2M4SEBSPSJTOQBXDI/",
    "mailinglist": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/",
    "message_id": "[email protected]",
    "message_id_hash": "Q2TRKWKDVYCKCAD2M4SEBSPSJTOQBXDI",
    "thread": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/thread/Q2TRKWKDVYCKCAD2M4SEBSPSJTOQBXDI/",
    "sender": {
        "address": "koos (a) kzdoos.xs4all.nl",
        "mailman_id": null,
        "emails": null
    },
    "sender_name": "Koos van den Hout",
    "subject": "[amsat-bb] Receiving with an rtl-sdr, desense on transmit",
    "date": "2017-04-30T19:57:23Z",
    "parent": null,
    "children": [
        "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/email/5XRM5V2LBMAAKF6JDJN764E2HWMIHLWU/",
        "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/email/LYI432FHVGC2SX43S3JE6MQF6BERJBML/"
    ],
    "votes": {
        "likes": 0,
        "dislikes": 0,
        "status": "neutral"
    },
    "content": "\nI am trying to go full duplex 'on the cheap' by using an rtl-sdr on the\nreceiving side, keeping an ear on the downlink while transmitting.\n\nSoftware wise this all seems to work. I use a linux setup, with gpredict to\ntrack the satellites and calculate doppler shift. The gqrx sdr software can\nact like a radio that gpredict can control so the receiving frequency is\ncorrect. It controls both gqrx as receiver and my ft-857 as transmitter.\n\nHardware wise I bought an rtl-sdr with a small preamp and built the pre-amp\ninto a metal case.\n\nThis works up to the level where I received AO-73 and received a weak\nFox-1A and recorded the pass.\n\nBut when I pressed the transmit button on the FT-857 (tuned to the 70cm\nuplink frequency) the receiver (tuned to the 2m downlink frequency) went\ndeaf.\n\nSome testing with the arrow antenna and transmitting on 70cm shows the\npreamp turns deaf on 2 meter. Even without the preamp but with the internal\namplifier of the rtl-sdr this happens. Setting the gain to 'automatic'\ncauses a huge drop in signal and takes time to recover.\n\nComplete details, experiences, pictures of my setup and details I left out\nstart at\nhttps://idefix.net/~koos/newsitem.cgi/1490542545\n\n- has anybody done anything with an rtl-sdr as the receiving side, how do\n  you setup the gain? Is there a solution to fix this?\n\n- specific to fox-1a: I am reading somewhat different reports of the\n  downlink and uplink frequencies when I search with google. I hope\nhttp://www.amsat.org/?page_id=4690 is right. I did notice the signal is\nweak even with an amplifier.\n\nThanks for any insights and tips,\n\n                                       Koos PE4KH\n\n-- \nKoos van den Hout           PGP keyid 0x5BA9368BE6F334E4 via keyservers\n                                             IPv6: Think ::/0, act ::1.\nhttp://idefix.net/              Are you ready to start supporting IPv6?\n",
    "attachments": []
}