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{
    "url": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/email/ISWKGHA73MGZDDSIMQ2PIRUVEQC3LRAU/",
    "mailinglist": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/",
    "message_id": "CAF3DnKh4fY3hWFn2HX1LCKJm-KLnfd1o5fEUeFiZU-_eE=3O4A@mail.gmail.com",
    "message_id_hash": "ISWKGHA73MGZDDSIMQ2PIRUVEQC3LRAU",
    "thread": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/thread/FJUGVZMYSLUOJT2NMMUML2VBEO2VL7QY/",
    "sender": {
        "address": "dan (a) post.com",
        "mailman_id": "8fbd55eb51ed4663a4067933c1d26387",
        "emails": "https://mailman.amsat.org/hyperkitty/api/sender/8fbd55eb51ed4663a4067933c1d26387/emails/"
    },
    "sender_name": "Daniel Cussen",
    "subject": "Re: [amsat-bb] Antenna Setup",
    "date": "2015-10-16T13:32:13Z",
    "parent": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/email/FJUGVZMYSLUOJT2NMMUML2VBEO2VL7QY/",
    "children": [],
    "votes": {
        "likes": 0,
        "dislikes": 0,
        "status": "neutral"
    },
    "content": ">ll your comments / feedback here, just one additional\n> question from me,\n> In real world / every day use - what difference does using X-Pol (Cross\n> Polarized) antennas versus\n> a straight beam mounted vertically ? - How much of a difference does it\n> make to the received\n> signals ?\n\nThis is the best site I have seen with good explanations:\n\nhttp://sv1bsx.50webs.com/antenna-pol/polarization.html\n\nMany/most satellites are not true polarised sources, rather just omni\nantennas on one side. Often they are not controlled so they spin and\ntwist. As a result they can appear to change from vertical to\nhorizontal to LHCP to RHCP.\n\nIf you have circular, and the satellite is linear, the worst case\n(according to the chart) is 3dB. while if you are vertical at the\nsatellite appears horizontal the worst case it 30dB. So in normal use,\nyou can change from 30dB fading to 3dB fading.\n\nSome polarisation switches have the option to remotely change from\nRHCP to LHCP to vertical and horizontal. Thus you can compare them all\nsuch as wimos unit:\nhttp://www.wimo.com/download/1808xx.pdf\n\nSometimes even true circular polarised sources, can reflect off\nsomething, (e.g. the solar panels on the ISS) and suddenly a RHCP can\nbecome LHCP.\n\nSo I think the answer is if you see sudden fading in the middle of a\npass, it may be due to difference of polarisation, but sometimes it is\ndues to the antenna pattern of the transmit antenna being away from\nthe Earth side of the satellite. The only way to know for sure is to\nswitch polarisations quickly and compare.\n\nI would consider it if buying a new beam and if you have elevation\ncontrol. Circular is also useful for ground contacts as DX stations\ntend to use Horizontal Beams, and mobile and base tend to be vertical\nomni. With RHCP you only have a 3dB loss to either user at the other\nend.\n",
    "attachments": []
}