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{
    "url": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/email/O3SWBMSW5WASC4RMMB2F4TPIAY5U57UT/?format=api",
    "mailinglist": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/?format=api",
    "message_id": "DE529F5BF2A04CE690C6A6C61D3BA08A@TNTCENTER",
    "message_id_hash": "O3SWBMSW5WASC4RMMB2F4TPIAY5U57UT",
    "thread": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/thread/YEM7HVT3HPMKHXC2URHZYCIGCZ2HV6DV/?format=api",
    "sender": {
        "address": "tnetcenter (a) gmail.com",
        "mailman_id": "05366e6d2c0a49ddb2ff91e355667842",
        "emails": "https://mailman.amsat.org/hyperkitty/api/sender/05366e6d2c0a49ddb2ff91e355667842/emails/?format=api"
    },
    "sender_name": "Jeff Moore",
    "subject": "[amsat-bb] Re: Circular Polarized Antennae",
    "date": "2010-08-25T16:58:27Z",
    "parent": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/email/YEM7HVT3HPMKHXC2URHZYCIGCZ2HV6DV/?format=api",
    "children": [],
    "votes": {
        "likes": 0,
        "dislikes": 0,
        "status": "neutral"
    },
    "content": "If you're going to post an ad, you should at least provide the proper \ncontact info like web-site etc. so that we can take a look at your \nproducts - don't leave us hanging.\n\nJeff Moore  --  KE7ACY\nCN94\n\n----- Original Message ----- From: \"Spectrum International, Inc\" \n<[email protected]>\n                John,  LA2QAA\n\n                           That was an interesting message you posted to\nthe -bb this morning.  It has many true observations; however there is\none serious mistake, an unforgivable error.\n\n Quote:\n                ......... particularly by the newcomers - who\napparently, and mistakenly, think that high power is necessary.\n It's  *NOT* . . . nor is an EME class aerial array necessary to work\nthe LEO satellites. Ditto circular polarisation.\n\nFACT:    polarisation is  *ONLY* circular along the boresight of an aerial.\n\nUnquote.\n                    Your polarization statement is not 100% accurate.\nUnfortunately most antenna manufacturers, who supply/sell \"alleged\ncircular\" polarized antennas do not state that their antennas are\ncircular polarized ONLY along the boresight. They conveniently (?) do\nnot mention that their alleged \"circular polarized\" antenna is only\ncircular polarized on boresight, that it is linear polarized at 90\ndegrees off of boresight and is elliptical polarized of varying ratio at\nall angles in between!\n\n              There is however one (and only one that I am aware of)\nantenna design that is circular polarized over its entire radiation\npattern. I refer you to the Q_uadrifilar Helix Antenna_ described by Dr.\nC.C.Kilgus in IEEE Trans., Vol. AP-16, July 1968, pp. 499-500. Also\nBricker, R.W. and Rickert, H.H.,  in RCA Engineer, Vol.20, No. 5,\nFebruary/March 1975. There is an excellent review by Walter Maxwell,\nW2DU, at http://www.IAG.net/~w2du/quadfinal.pdf.\n\n             When installed pointing to the zenith, the \"ideal,\ntheoretical\" Quad Helix has 360 degree coverage in the azimuthal plane\nand 90 degree coverage in the elevation plane. It is circularly\npolarized over the entire upper hemisphere. There is no radiation in the\nlower hemi-sphere; the energy in the lower hemi-sphere of an isotropic\nradiator is uniformly distributed over the upper hemi-sphere. Hence the\ngain of an \"ideal\" Quad Helix is 3.01 dBi. However you can modify the\nelevation pattern to give more gain at the horizon and less gain\noverhead by adjustment of the overall length to diameter ratio. It is\npossible to adjust this ratio to give constant signal amplitude, at an\nearth based receiving station, from a satellite in a circular orbit\nwhere the range ratio (and hence signal path attenuation) between AOS\nand the zenith can be significant. This results in a little radiation\nbelow the horizon and also avoids the nasty mathematical boundary value\nproblem at the horizon in the ideal case.\n\n               Quadrifilar Helix antennas are used on many LEO\nsatellites  for VHF, UHF, L-band and S-band communication.  One of\ntheir  parameters of interest to satellite builders is that they do NOT\nrequire a \"ground plane\" provided they are at least a quarter wavelength\nabove the satellite structure. Hence there is negligible critical\nlocation requirement and they do not occupy satellite surface area that\nis required for solar cells.\n\n                The Quadrifilar Helix antenna is popular with earth\nbased receiving stations for receiving the VHF image data signals from\nthe NOAA weather satellites. Right-hand circular Quad Helix antennas for\nthe 137MHz NOAA weather image signals and 137MHz left-hand circular Quad\nHelix antennas for receiving the ARGOS  programme signals, are available\nfrom Spectrum International, Inc. Spectrum also supplies both right-hand\nand left-hand versions for the 2M and 70cm Amateur radio bands.\n\n                May we suggest you sprinkle some \"Grow More fertilizer\"\naround the base of your \"chopped down satellite array\" every Sunday\nmorning and offer a few words of wisdom while so doing. With a little\nhelp and the dregs of Saturday night's Black and Tan, your mini array\nmight grow.\n\n                Regards,     Spectrum.\n\n\n\n\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": []
}