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{
    "url": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/email/ERTHDWTXUGJFHBSMWHIBDBLJR427CYU7/",
    "mailinglist": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/",
    "message_id": "[email protected]",
    "message_id_hash": "ERTHDWTXUGJFHBSMWHIBDBLJR427CYU7",
    "thread": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/thread/5HCWDGY7NTFKXMOTF2O7KEJMGKDL6VW4/",
    "sender": {
        "address": "karn (a) philkarn.net",
        "mailman_id": null,
        "emails": null
    },
    "sender_name": "Phil Karn",
    "subject": "[amsat-bb] Re: Decoding wideband recordings",
    "date": "2011-08-19T03:11:44Z",
    "parent": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/email/OW6Q2EAX7DYRM6OPFIQHC2Y5YXM7URNA/",
    "children": [],
    "votes": {
        "likes": 0,
        "dislikes": 0,
        "status": "neutral"
    },
    "content": "On 8/18/11 8:15 AM, Patrick Strasser OE6PSE wrote:\n\n> For decoding please be aware that I/Q via sound interfaces has a weak\n> spot at the centre frequency. The interfaces all have a high pass\n> characteristic below like 30Hz, which means the resulting spectrum has a\n\nYes, I'm familiar with this. I will ask users to put this notch in the\ncenter of the transponder band (145.938 MHz) so that the BPSK-1000\nbeacon will appear at about -18 kHz. 0 Hz will correspond to the notch,\nthe transponder will appear between -16 kHz to 0 Hz and the FM signals\n(voice, sstv) will appear in the positive frequencies centered at +12 kHz.\n\nIt will be easier if Doppler is *not* corrected for so I can do that in\nsoftware. This will move the notch +/- 3.3 kHz around the center of the\npassband, and that might interfere a little with the top of the\ntransponder passband between AOS and closest approach.\n\nIf for some reason the I/Q channels are swapped or there's a polarity\ninversion simply flipping the sign on the frequency should take care of\nit. The BPSK-1000 signal is symmetric so it can tolerate sideband\ninversion. (USB reception on a conventional SSB receiver is recommended\nonly because the CW beacon is 1 kHz below the BPSK-1000 beacon. This\nputs the CW beacon at an audio frequency of 500 Hz when the BPSK-1000\nsuppressed carrier is at its nominal 1500 Hz. It could be received just\nfine in LSB mode but then the CW beacon would have to be tuned to an\nuncomfortably high pitch of 2.5 kHz, and it would be harder to tune it\naccurately by ear.)\n\n> What I wonder is how good BPSK1000 survives speech encoders, like MP3.\n> Is there any experience already?\n\nMuch to my amazement, during prelaunch testing I was able to decode\nBPSK-1000 that had been run through lossy codecs like MP3. But I don't\nrecommend it. If the recording data rate is a problem, reduce the\nsampling rate while ensuring that the 2 kHz wide BPSK-1000 signal is\ncompletely captured within the Nyquist bandwidth of your A/D converter.\nE.g., 8000 or 9600 Hz should be fine provided the BPSK-1000 signal is\ncentered at 1500 Hz. Although the demodulator assumes an A/D sampling\nrate of 48 kHz, a recording with a lower sampling rate can be converted\nback to 48 kHz with a program like 'sox' as long as the information is\nstill there.\n\n73 Phil\n\n\n",
    "attachments": []
}