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{
    "url": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/email/5CZ6ALWCNYFXDFBIMFPAPEW7ZFSNKDRO/?format=api",
    "mailinglist": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/?format=api",
    "message_id": "000301c7babd$de2488b0$0301a8c0@Shop",
    "message_id_hash": "5CZ6ALWCNYFXDFBIMFPAPEW7ZFSNKDRO",
    "thread": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/thread/KK75DA42V2CVIKOT3KCXESRATCF6E3X2/?format=api",
    "sender": {
        "address": "juan-rivera (a) sbcglobal.net",
        "mailman_id": null,
        "emails": null
    },
    "sender_name": "Juan Rivera",
    "subject": "[eagle]  CAN-Do EMI - Let's Get Going on This!",
    "date": "2007-06-30T02:25:01Z",
    "parent": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/email/VRTXAP7HKE3CD2EJOJUXHBO7NG3IO6GE/?format=api",
    "children": [
        "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/email/SAEALDNH5ODPS3Z23PPXRQFT6E765JAB/?format=api"
    ],
    "votes": {
        "likes": 0,
        "dislikes": 0,
        "status": "neutral"
    },
    "content": "Bdale,\n\nI'm sorry to pick on you, but you seem like a good guy to complain to...\n\nI seem to be having a problem stimulating a discussion.  After saying that I\nthough the CAN-Do power supply needed to be completely scrapped and replaced\nwith one running at around 1 MHz I expected to be buried in email, but I've\nonly received one message referring to this so far, and it wasn't from\nanyone working on CAN-Do.\n\nThe CAN-Do module is unique in that it is going to be an integral component\nINSIDE of every payload, so any deficiencies it may have are going to have a\nlarge impact.  \n\nLet me restate my finding so far:\n\nThere are 4 categories of EMI and the CAN-Do module / 70 cm Receiver\ncombination is experiencing all four.  They break down into radiated and\nconducted emissions and susceptibility, and they are generally referred to\nby a two-letter designation - RE, RS, CE, and CS.\n\nRE and RS go together - the CAN-Do module's switching power supply inductor\nradiates the 5 kHz switching noise out the back directly towards the\nreceiver (RE.)  The Receiver's VCO's are both very sensitive to EMI and are\nimpacted by the CAN-Do module if they are within 4-1/2 inches of the\ninductor (RS.)  I've had to move the CAN-Do module off of the receiver PCB\nand interconnect it with a ribbon cable to deal with this problem.  The good\nnews is that I am fairly confident that It can be fixed by going to a\ntwo-compartment chassis, with a bulkhead separating the CAN-Do module from\nthe analog Receiver to provide shielding.  The bad news is that I think this\nmeans we need a milled module chassis.\n\nCE and CS also go together, and this is the real problem I see since you\ncan't fix conducted EMI with a shielded enclosure.  It requires filtering.\nThe CAN-Do module is trashing the DC input from the power source and also\nfeeding noisy power to the Receiver.  The outgoing noise is the bigger\nconcern because it will add to the CS problems for everything connected to\nthe power source.  In the other direction, the switched power from the\nCAN-Do module shows up in the IF output as 5 kHz spurs.  Moving the CAN-Do\nmodule physically away from the Receiver only dealt with the RE/RS issue.  I\nhad to bypass the CAN-Do module and run clean power directly from the lab\nbench supply to deal with the CE/CS problem.  This means that there is no\ncurrent monitoring and no power control.\n\nThe 5 kHz switching frequency is bad for two reasons - it makes filtering\nthis noise a much larger problem than it needs to be, and the impact is more\nsevere since it is putting spurs all over the passband of the IF at 5 kHz\nintervals.\n\nIf you sit back and think about the impact of a dozen noisy power supplies\nall feeding EMI back to the common power source where they all mix together\nand make their way back to each payload, it starts to look nasty.  All these\nsupplies will be drifting around and beating with each other to produce sum\nand difference noise on the power bus.  5 kHz noise is hard enough to get\nrid of but what if there are difference components at a few hundred Hz?  How\ncan you design a filter when you won't know what to expect until you hook\neverything up and turn it on?  And by then you're out of time.\n\nI'm not making this stuff up.  People I know have run into this exact\nproblem before and the result was very bad.\n\nA while ago Howard Long made a suggestion that I think has great potential.\nHere's what he had to say:\n\n...in the original SDX PSU design I had in San Francisco last year is an\nSMPS using the LM2672 device. These can be fitted with an AC coupled SYNC\nsignal to override the internal default SMPS frequency. I selected 375kHz\nfor my unit (6MHz divided by 16) to ensure its harmonics were outside the\n10.7MHz IF passband. If the external SYNC fails the internal SMPS oscillator\ntakes over.\n\nMy Suggestions:\n\n1) Revise the CAN-Do module to move the switching frequency up as far as\npossible to move spurs out of the passband of sensitive analog circuitry,\nand to ease the burden on EMI filtering.\n2) The power and grounds must be filtered in both directions to minimize CE\nback to the power source and to the payload.\n3) The switching inductor should be a shielded to reduce RE inside the\nmodule chassis.\n4) A power supply capable of synching to a master oscillator should be\nstrongly considered.\n\nThis topic needs to be elevated to the top of the queue.  The EMI\nenvironment surrounding the CAN-Do module impacts the design of the next\nrevision of the 70 cm Receiver, and also directly impacts the chassis\ndesign.  What do we need to do to get going on this?\n\n73,\n\nJuan - WA6HTP  \n\n\n\n\n\n",
    "attachments": []
}