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{ "url": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/email/WO5BBCGWJGYFFUSQUMHKSRAX3LNB7DKZ/", "mailinglist": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/", "message_id": "[email protected]", "message_id_hash": "WO5BBCGWJGYFFUSQUMHKSRAX3LNB7DKZ", "thread": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/thread/WO5BBCGWJGYFFUSQUMHKSRAX3LNB7DKZ/", "sender": { "address": "kf6kyi (a) gmail.com", "mailman_id": null, "emails": null }, "sender_name": "Mark Vandewettering", "subject": "[amsat-bb] bbsat ideas...", "date": "2008-11-25T04:56:44Z", "parent": null, "children": [ "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/email/WU6WHIMMTPUBKC5G7WPXBXYWYH7ZTJCK/", "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/email/TQMC3AT5X6ERX3BNLBQ3MZNWZGK2MNBN/" ], "votes": { "likes": 0, "dislikes": 0, "status": "neutral" }, "content": "\nNice thought provoking question, Joanne. Here's an off-the-cuff \nidea. I haven't tried to work out any of the numbers, it's just some \nidle musing.\n\nIt has occurred to me that we are in the midst of a minor revolution \nin amateur radio (which will undoubtedly be followed by a more major \nrevolution). In the last 10 years, cheap computing and sound cards \nhave caused a great deal of experimentation with \"sound card \nmodes\" (the minor revolution), and will ultimately lead to the major \nrevolution (widespread use of SDR). We have a kind of flexibility \nthat we couldn't think of even a few years ago, a flexibility that we \ngain from Moore's law.\n\nSo here's an idea: let's do away with the need for Doppler correction \nentirely. It's not like we don't have decent orbital elements for the \nsatellites that we use. It's not like our ground stations don't have \naccurate timing information available to them. Even if we didn't, we \ncould still output a (coded?) carrier that our\nsoundcard modem could lock onto, and then transmit relative to that \nfrequency.\n\nGiven the relatively limited amount of power that we are likely to \nhave in a cubesat, the question then becomes what is the best way to \nuse that power? It seems unlikely that any kind of linear \ntransponder will allow more than just a couple of users meaningful \naccess. I'd suggest it might make more sense to do some kind of \ndigital transponder. I'm imagining a satellite which monitors a \nchunk of spectrum roughly the size of a current SSB signal, say \n2.4khz. Imagine that space was divided into (say) 10 channels, each \n240hz wide. We could easily fit a PSK63 signal (or a similar FSK \nsignal, pick your poison) in that space. You could use a bent pipe \ncrossband transponder, or potentially do a simplex repeater (say the \nsat listens for 10 seconds, then re-echoes for 10 seconds) on the same \nuplink frequency. If you are a downlink station, you know what you \nsent, and can tell if your signal got collided with, and if so, you \ncan switch to another of the 10 slots. In the mean time, you can \neasily monitor all of the other slots as well, and try to pick an \nunoccupied one. While it might be difficult for a power-efficient \ncontroller to actually _decode_ each of the 10 channels, it probably \ncould determine which channels are busy itself by monitoring power in \neach of the channels. Maybe we can fill\nunused slots with telemetry? Or can we actually get enough DSP power \ninto a cubesat to decode 10 channels of PSK (or some similar \nprotocol), which would help a lot (the bird only transmits stuff, and \nwhat it transmits is free from noise/errors). If not 10 channels, \nthen how 'bout 5? 2? Even one? Then, we basically have a simple \ndigipeater, which can obviously be done, given the existance of 1200 \nbaud modems based upon PIC microcontrollers.\n\nJust some lunacy...\n\n\tMark KF6KYI\n \n", "attachments": [] }