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{
    "url": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/email/AUT32NYJUACBSEPTLOSYWXGTXWAHLBKP/?format=api",
    "mailinglist": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/?format=api",
    "message_id": "[email protected]",
    "message_id_hash": "AUT32NYJUACBSEPTLOSYWXGTXWAHLBKP",
    "thread": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/thread/H2N2VWPFCJJ3WI6RDAFJNA36SA32ZJS4/?format=api",
    "sender": {
        "address": "zleffke (a) vt.edu",
        "mailman_id": "57a24afb1cf641f98121841e6753c12e",
        "emails": "https://mailman.amsat.org/hyperkitty/api/sender/57a24afb1cf641f98121841e6753c12e/emails/?format=api"
    },
    "sender_name": "Zach Leffke",
    "subject": "[amsat-bb] Re: Help wanted on CP antenna design",
    "date": "2013-07-17T12:59:58Z",
    "parent": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/email/BZFUPPJZ5ML2CBAW7DTV2GFAJRNDSJRD/?format=api",
    "children": [],
    "votes": {
        "likes": 0,
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        "status": "neutral"
    },
    "content": "Hi Phil,\n\tI've flown a couple of balloons as an advisor to an undergraduate\nlab here at Virginia Tech.  We use CP on all of our flights, though\ngenerally we use the standard 2m APRS freq and not 70cm.  Our first two\nflights we flew a crossed dipole suspended above the payload (to get it out\nof the view of the down facing camera) and had excellent results.  Our\nsecond flight flew the Byonics MicroTrak 300, with only 300 mW of power and\nhad no problems hitting digipeaters and iGates from 100,000+ feet.  The\ncrossed dipole was constructed out of aluminum arrow shafts (rigid, but\nlightweight).  In an effort to drop even more weight, we changed to a design\nthat uses fairly rigid wire in a \"turnstiled loop\" configuration, more\ncommonly known as an eggbeater, again with excellent results from flight.\n\tIn both cases we decided to forego installing the ground plane\nmentioned in previous posts.  This was primarily a design decision made to\nsave weight at the loss of a few dB (energy radiated up does us no good with\nreceivers on the ground).  One design that I have wanted to try but haven't\nyet had the opportunity is the crossed moxon.  Essentially, it is like\ntaking the reflector and driven elements of a pair of yagis and crossing\nthem at 90 degrees.  It is slightly different from the Yagis as the end of\nthe reflector is bent 90 degrees toward the driven and the driven ends are\nbent 90 degrees towards the reflector (for impedance manipulation).  L.B.\nCebik, W4RNL, wrote a very useful article in the August 2001 edition of QST\ndescribing the construction of the crossed moxon, complete with design\ndimensions for a 435.6MHz crossed moxon (google can direct you to a copy of\nhis article).  I do not have information about the cross-pole rejection, but\nsome time spent with 4NEC2 antenna modelling software may give you a bit of\ninsight.  \n\tWith the bends in the elements of the moxon it focuses the pattern a\nbit more towards the horizon (over the crossed dipoles).  I'm not sure about\nyour location, but for us in SW Virginia our balloons get whipped right\nalong in the jet stream and we have trouble keeping up with them during the\nchase (peak lateral speed in the Jetstream for our flights was 143 MPH).\nThe result of this is that at no time (other than the initial release when\nthe balloon is under about 10,000 ft) does the balloon get much higher than\nmaybe 20 degrees elevation.  Having energy focused more towards the horizon\nand less towards zenith (both in the balloon antenna and the ground\nantennas) is probably not a bad Idea in our case.\n\nIf you search callsigns KK4MOB and KK4PWM on aprs.fi you can see the path of\nour flights and the insanely high speeds in the Jetstream (around 30k-40k\nft).\n\nHope the responses help inform your decision.\nGOOD LUCK!\n\n-Zach, KJ4QLP\n\n-----Original Message-----\nFrom: [email protected] [mailto:[email protected]] On\nBehalf Of Zilvinas, LY2SS\nSent: Wednesday, July 17, 2013 6:33 AM\nCc: AMSAT BB\nSubject: [amsat-bb] Re: Help wanted on CP antenna design\n\n\nOn 2013.07.17 10:11, Simone wrote:\n> Hi Phil,\n>\n> QFH is effectively circularly polarized, it is often used for GPS \n> receivers, since when you point it skywards the main lobe points \n> trough the zenith, while nulls are pointing to the horizon (where you \n> do not have satellites normally).\n>\n> In my opinion QFH risks to be quite bulky for a balloon, since it will \n> occupy a cylinder 1 wavelength high (70cm in your case).\n>\n\nQFH for 70cm band is 264 mm height only (and 84 mm in diameter).\n\n73!\n_______________________________________________\nSent via [email protected]. Opinions expressed are those of the author.\nNot an AMSAT-NA member? Join now to support the amateur satellite program!\nSubscription settings: http://amsat.org/mailman/listinfo/amsat-bb\n\n",
    "attachments": []
}