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{ "url": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/email/6AVXHXMM325MMPLEDGLUZMGCRK7WPJ2Z/", "mailinglist": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/", "message_id": "000801c7db86$ca0f7620$0301a8c0@Shop", "message_id_hash": "6AVXHXMM325MMPLEDGLUZMGCRK7WPJ2Z", "thread": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/thread/6AVXHXMM325MMPLEDGLUZMGCRK7WPJ2Z/", "sender": { "address": "juan-rivera (a) sbcglobal.net", "mailman_id": null, "emails": null }, "sender_name": "Juan Rivera", "subject": "[eagle] Proposed 70 cm Receiver plan - Let's get this project going!", "date": "2007-08-10T19:43:54Z", "parent": null, "children": [ "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/email/EWEFJZGNX5YNGPH7KS2V5KZ3YIQ7WC3U/" ], "votes": { "likes": 0, "dislikes": 0, "status": "neutral" }, "content": "All,\n\n \n\nThe 70 cm Receiver has been stuck in a rut for too long. Now that I've\ncompleted my Symposium presentation I'd like to get it back on the tracks\nand moving forward again. Here's the way I see it:\n\n \n\nPassband Ripple - we want to understand this problem before proceeding with\nthe next upgrade revision so we don't end up with another prototype that\nstill has excessive ripple. John will design a new PCB that will act as a\ntest fixture for the 199 MHz 1st IF string. Parts will be distributed to\nJohn, Bill Ress and to me. We will all work this problem in parallel.\n\n \n\nThe PCB will also contain test fixtures for any other portions of the\nreceiver that we want to characterize independently of the receiver. The\nvarious fixtures can be cut apart once the PCB is fabricated. I'd suggest\nthat the proposed analog replacement 10 MHz reference be included. I'll run\nthat in my temperature chamber.\n\n \n\nCAN-Do Module - No one has volunteered to work the power supply issue so\nI'll do it. It's my belief that the existing step-down converter is running\nat a much lower efficiency that anyone realizes. I'll test this theory and\nreport back. It appears to be a generic characteristic of this type of\nconverter that the efficiency drops off towards zero at very low output\ncurrents. As I've discussed in my logs, this one is only putting out 11\nmilliamps. This could also explain the motorboating that I have observed.\nSo far I have not found any other switching step-down converter that is\noptimized for this low output current. This problem needs to be resolved\nnow since it impacts the design of the enclosure. If we go to an analog\nregulator the CAN-Do conducted and radiated EMI problem will be completely\neliminated. If we stay with a switching step-down converter then we may\neither need to move to a two-compartment enclosure or vacate the front third\nof the existing enclosure to escape the CAN-Do radiated EMI.\n\n \n\nThe Enclosure - I put forth a recommended enclosure requirement calling for\na worst case PCB flex of 0.0084\" in any one-inch segment. No one has made\nan argument against this. I do not believe that the current sheet metal\nenclosure with attached self-clinching standoff mounts and three separate\nheat sinks can meet this proposed requirement over the proposed temperature\nrange which extends down to -60*C. With the current design that attaches\nthe CAN-Do module to the main PCB via the 40-pin header and then fixes the\nCAN-Do module to the front panel, there is no room for any flexing or\ntwisting between the base plate and front panel since those induced stresses\nwill be transferred directly to the solder joints on the 40-pin header. The\nsheet metal vs. milled enclosure questions needs to be resolved.\n\n \n\nLow temperature Operation - The minimum operating temperature of the SAW\nfilters is -35*C and the minimum storage temperature is -40*. For the IC's\nthe minimum operating temperature is -40*C and the minimum storage\ntemperature is -65*C. These temperatures are not just guesses on the part\nof the manufacturer. They are a function of the difference in thermal\ncoefficient of expansion between the various internal parts of the devices.\nOperation below the minimum operating temperature will cause premature\nfailures to develop in short order. The worst case scenario would be to\npower up the Receiver after is had cold soaked to -60*C. The silicone would\nheat up very quickly and begin to expand. The thermoplastic case material\nwould lag behind and expand at a different rate causing large internal\nstresses. I have not seen a final word on the minimum temperature that the\nReceiver will see in orbit. If it really is -60*C then I propose that a\nspace-rated thermal switch in placed in series with the DC power to prevent\nactivation below -40*. Even this thermal switch proposal side-steps the SAW\nfilters which cannot withstand -60*C. The proposed work around of splitting\nthe receiver into two sections adds complexity which reduces reliability. A\nway needs to be found to keep the receiver from dropping below -40*.\n\n \n\nExternal EMI from the primary power source - The next revision of the\nReceiver needs to include EMI filtering and possible shielding to deal with\nradiated and conducted EMI from all sources. These sources need to be\nidentified and characterized so that the Receiver can be designed properly.\nIt makes no sense to press on with the next revision upgrade until this is\nsorted out.\n\n \n\nReceiver Requirements vs. ATP - The ATP contains tests for which there are\nno requirements. We need to harmonize these two documents and do a new peer\nreview for both.\n\n \n\nLet's get these items resolved!!\n\n \n\n \n\n73,\n\n \n\nJuan - WA6HTP\n\n\n\n", "attachments": [ { "email": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/email/6AVXHXMM325MMPLEDGLUZMGCRK7WPJ2Z/", "counter": 2, "name": "attachment.html", "content_type": "text/html", "encoding": "us-ascii", "size": 9636, "download": "https://mailman.amsat.org/hyperkitty/list/[email protected]/message/6AVXHXMM325MMPLEDGLUZMGCRK7WPJ2Z/attachment/2/attachment.html" } ] }