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{ "url": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/email/R7TO6BWWJJA6E3SXP3VDV55RN6ZHEE42/?format=api", "mailinglist": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/?format=api", "message_id": "000001c7c2a1$5e2625b0$0301a8c0@Shop", "message_id_hash": "R7TO6BWWJJA6E3SXP3VDV55RN6ZHEE42", "thread": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/thread/RQX4DLDIYY3MVVVNFRFO357N5UXLTUIQ/?format=api", "sender": { "address": "juan-rivera (a) sbcglobal.net", "mailman_id": null, "emails": null }, "sender_name": "Juan Rivera", "subject": "[eagle] Re: CAN-Do-Too! ??????????", "date": "2007-07-10T03:21:11Z", "parent": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/email/O7OOEZTG7IS35OKT7SV3B4FP3CHGWLXF/?format=api", "children": [], "votes": { "likes": 0, "dislikes": 0, "status": "neutral" }, "content": "Jim,\n\nI concur completely with Bill,\n\nI beg you, don't open that MIL spec! Abandon all hope ye who enter there!\nThere are actually two specs. One is how to test and the other is what the\ngovernment wants to see for EMI shielding on tanks, ships, aircraft, etc.\nThey're both impractical for our purposes.\n\nWhat is does offer is a method of describing EMI so we can all discuss it.\nThey break it down into 4 categories':\n\nConducted Emissions\nRadiated emissions\nConducted susceptibility\nRadiated susceptibility\n\nI agree with Bill. Guessing about something as universal as the quality of\nthe primary power is not a good way to start. We need to characterize\n\"noise\" from the perspective of the power distribution point. The amplitude\nand spectral distribution of the conducted EMI coming out of there is a\ncritical item. The same goes for the switched power from the CAN-Do module.\nThose two sources of noise will impact everything on the spacecraft.\n\nThat leaves radiated emissions and susceptibility to nail down. This is\nwhere it impacts the module chassis directly. Can we get by with one\ncompartment with digital and analog circuitry together? This is generally\nconsidered a very bad design practice. But we'll only be able to tell after\ntesting, and then it may only apply to the 70 cm Receiver so we have to be\ncareful. Some effort should be expended identifying other payloads that may\nhave EMI susceptibility issues - receivers, magnetometers, etc...\n\nI think this is a good example of the phase, \"measure twice and cut once\".\nIf the requirements are unrealistic you'll find out very late in the\nintegration phase when there is no time to fix anything.\n\nLastly, we need to be able to generate a realistic noisy power source for\ntesting. It needs to be capable of being duplicated so we can have multiple\nunits for each team to use. Once we have a realistic noise source then we\ncan come up with a series of tests to determine if the unit meets the specs.\n\n73,\n\nJuan\n\n\n-----Original Message-----\nFrom: [email protected] [mailto:[email protected]] On Behalf Of\nBill Ress\nSent: Monday, July 09, 2007 7:34 PM\nTo: Jim Sanford\nCc: [email protected]\nSubject: [eagle] Re: CAN-Do-Too! ??????????\n\nJim Sanford wrote:\n> 4. EMI Spec: You put a gun to my head, and I'm going to pull out the \n> MIL-STD, which is probably overkill, but MAYBE NOT. I'd really prefer \n> that one of you guiys current in the INDUSTRIAL world take on this \n> task and come up with something good enough and reasonable. In \n> general, I'd like to eliminate as much mass and extra \"touch\" labor in \n> the assembly process (multiple shields) as possible. Bob Davis: \n> Please weigh in here, if the possible milled modules simplify this \n> issue, please enlighten us.\nJim, I think an EMI spec pulled out of a MIL-STD would be an over kill \neffort and likely not representative of \"our\" real world. What we need \nis not assumptions but data reflecting what the hardware does. The \nproblem is that we don't have the hardware - and that's my issue. The \npower distribution circuits are what I call a \"top level\" subsystem \nwhich feeds \"everyone.\" Instead of working on the circuitry that will \nrun from it and trying to \"imagine\" what we can expect, let's focus on \nbreadboarding the key power distribution circuits and get some hard data \nso we know what we're working with.\n\nI'll again reiterate (as I have several times in the past) the same \nthing for the satellite's 10 MHz reference. It's another top level \n\"subsystem\" that will feed \"all\" LO's. Instead of guessing what we'll be \nworking with, let's get it defined too.\n\n(I'm proposing we put that one to bed and use the time tested, well \ndefined, high stability, low noise HP (OK - Agilent) 10811 series of \nreference standards used in most of their test instruments. If that \nwon't cut it - someone please tell me why!)\n> 7. Requirements: Bob McGwier is correct, we really did start with a \n> very top-level requirements document. It is not perfect (Bob has \n> hated it from the word go), but can be found on EaglePedia under \n> Functional Requirements. It is also in need of updating, after the \n> October BoD decision. On my list to do. Like you, I have finite \n> energy and time, but it is on my list. I think John did an EXCELLENT \n> job of documenting the UHF Receiver requirements based on what he \n> knew. The need for an EMI spec was not obvious, but is now, thanks to \n> Juan's testing efforts and exceptional documentation. Lou: \n> Functional requirements for power supplies? Bob Davis: Functional \n> requirements for structure and thermal performance? etc. etc.....we \n> have much to do, but I think worthwhile effort. By the way, I'm \n> reading (in a few spare minutes here and there) an EXCELLENT book on \n> requirements management. When I finish, look for a review of it on my \n> project management page. I will also be providing suggestions on \n> writing \"good\" requirements, based on that book and my recent \n> experiences in the day job.\n>\nYes, we have \"top level requirements\" for desired satellite functions, \noperating modes and parameters and link budgets. But again, I think \nwe're sorely lacking in key \"system\" performance requirements based on \nreal data - - - which can only be obtained by building and testing \nthese key functions.\n\nI'm not a power supply guy, but I'll offer to assist in building and \ntesting the circuits we need to characterize. Lou - point me in the \nright direction - tell me what you need!\n\nRegards...Bill - N6GHz\n\n_______________________________________________\nVia the Eagle mailing list courtesy of AMSAT-NA\[email protected]\nhttp://amsat.org/mailman/listinfo/eagle\n\n\n", "attachments": [] }