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{ "url": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/email/QBIE4P4HVO2VOIYOEOS2UON4MPIV34AU/?format=api", "mailinglist": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/?format=api", "message_id": "[email protected]", "message_id_hash": "QBIE4P4HVO2VOIYOEOS2UON4MPIV34AU", "thread": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/thread/AMZGDYJTDVRYUX2WF3QHR6TONUWEXQPV/?format=api", "sender": { "address": "emily (a) clarke-design.com", "mailman_id": null, "emails": null }, "sender_name": "Emily Clarke", "subject": "[eagle] Re: [Fwd: [amsat-bb] Re: S band downlink on P3E]", "date": "2006-09-08T04:28:21Z", "parent": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/email/PREHVYZ4EIGD6IWA4S6AOSGBJRI64FTZ/?format=api", "children": [ "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/email/GSSBHN52EIWTG3EA4JJO6YAQE3NL5XJI/?format=api", "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/email/QONVA6E7ZCE33UOQINGJUQT4DV5BUWDF/?format=api" ], "votes": { "likes": 0, "dislikes": 0, "status": "neutral" }, "content": "I rarely post to this list but I hope you will accept my apologies \nfor doing so on this topic.\n\nAt 05:31 PM 9/7/2006, Matt Ettus wrote:\n\n>I have a few problems with this.\n>\n>1 - It has bad selection bias. Amateurs who are already on satellites\n>and who use S-band downlinks are the ones who don't have problems with\n>interference. If they had interference, they wouldn't be on those\n>bands.\n\nThis is IMHO a very bad assumption. If this was a problem with AO-40 \nor AO-51 (since the assumption is the problem grew expotentially \nsince 2003) then I think we would have heard volumes about it. We \nhaven't. I would be the first to defend that AO-51 is not the best \nexample to use, but I swept my yagi and downconverter around 360 \ndegrees with my spectrum analyzer attached. The spikes were s1 or \nbelow. It's not a calibrated measurement, but I'd have to side with \nthe \"this isn't a problem\" folks. So I feel strongly more tests are needed.\n\n>Additionally, people currently on satellites tend to be those\n>with lots of space for big dishes.\n\nI live in a townhouse - this is again a bad assumption. I work AO-51 \nwith a Yagi for 2.4G. If the wind conditions here in San Mateo are \nlight (which they generally aren't) I might put put up a 60CM dish, \nbut generally I won't. Even with the Yagi - WiFi is not a problem.\n\n> The point here is to open this up to\n>people who won't, and would have more interference problems, since they\n>live in denser areas and can't put up big dishes with lots of\n>directional gain.\n\nSan Mateo has almost a million people in a 12 mile radius. I get no \nlittle inteference in the lower S band, and only a very small amount \nof popping (that my DSP removes completely) in the upper S band. So \nI personally need more convincing that this isn't a problem. At \nworse we may have to convince our members to buy better \ndownconverters or add on notch filters so that their wideband \ndownconverters don't suck up noise from outside the band. But \ntelling people to get a filter isn't a big inconvenience. It's been \ndone before.\n\n>2 - Anecdotal \"evidence\" is pointless, especially since it is 5 years\n>old. WiFi is a lot more popular now than it was 5 years ago.\n\nMatt, I don't want to seem confrontational, but so far all I've seen \nis anecdotal eveidence from the Eagle team. I will admit I don't \nread everything, but I do read things more closely when I see things \nlike camera shots from spectrum analyzers that are real \nexperiments. I haven't seen it.\n\nIt is important to provide empirical data. I have a very open mind, \nbut so far the only thing I've seen are predictions of impending doom \nand statistics, not hard data.\n\n>3 - Could you justify putting up an X million dollar satellite that uses\n>a band which is questionable at best, just because some complainers who\n>don't actually volunteer to do anything say that it works for them?\n\nI think this is a very good question - so if that is the argument, \nwhy would you put up a mode U/V transponder? It's as usable as mud \nin a gas tank.\n\n>4 - Why should we have to justify why we're not using a band?\n\nThere are several reasons. The first is because we have spectrum \nallocated there, and if we don't use it we simply lose it. In the \nfuture we may need to rely upon it.\n\nThe other reason is because the people who bought into the technology \n5-10 years ago have an investment that hasn't yet been fully \nrealized. I don't want to go down the road questioning the judgement \nof people who told our customer base to go down the road, but if it \nwas flawed we haven't told people we are sorry. It's also why none \nof the commercial broadcasters cut off analog TV transmissions when \nthe FCC set the 2006 deadline. People hang on to technology.\n\n> As we\n>agreed at the SD meeting, we are looking at providing _services_ and the\n>best way to do that, not how to best make use of old hardware, which\n>wouldn't be usable anyway.\n\nI wasn't invited to that meeting, but can you tell me why you don't \nthink it wouldn't be usable? I think that is a very bad assumption.\n\n>X-band is usable too. Why isn't anyone\n>asking us to justify not using it?\n\nI'm not an expert at that level of microwave technology, but I think \nthat the biggest hurdle (and I could be slammed here) is that if we \nwere to try to launch an X-Band satellite I'm not sure the baseband \noscillator technology would be stable in space at a price we can \nafford. Rick can comment on that - he's the GPS expert and I'm \ncommenting with only terrestrial experience. But putting a GPS \ncorrected clock for X-Band stabilization is something we haven't \ntried before. However, perhaps we should, and I think the membership \nwould get behind that experiment.\n\n73,\n\nEmily\n\n", "attachments": [] }