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{
    "url": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/email/BEBWZF3B7I4M2IRZ7GODPT57GODACRWY/?format=api",
    "mailinglist": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/?format=api",
    "message_id": "BBAE1107C7A1402CB450DE63DB705FBC@clarePC",
    "message_id_hash": "BEBWZF3B7I4M2IRZ7GODPT57GODACRWY",
    "thread": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/thread/KMU7PWXGI6OJ4VUKIBFC3CDAFTM2IYMA/?format=api",
    "sender": {
        "address": "clarefowler (a) rogers.com",
        "mailman_id": "e6ff4277069b46a8b5f3282d1c5b595a",
        "emails": "https://mailman.amsat.org/hyperkitty/api/sender/e6ff4277069b46a8b5f3282d1c5b595a/emails/?format=api"
    },
    "sender_name": "Clare Fowler",
    "subject": "[amsat-bb] Re: Arrow and ELK Comparative Antenna Tests",
    "date": "2011-04-26T16:19:07Z",
    "parent": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/email/KMU7PWXGI6OJ4VUKIBFC3CDAFTM2IYMA/?format=api",
    "children": [],
    "votes": {
        "likes": 0,
        "dislikes": 0,
        "status": "neutral"
    },
    "content": "It is commendable to see some direct antennas comparison measurements being \nmade.\nComputer modeling is one thing. Realizing it in hardware is quite another.\n\nThe biggest problem in making field measurements is to reduce and try and \neliminate reflections\nfrom the ground, adjacent structures and overhead wires and your antenna \nmount.\n\nThe pattern of the antennas under test can be very significant.\nTwo antennas can have the same direct forward gain. But one can have\na narrow beam width main lobe but with relatively large side lobes,\nwhile the other has a broader main lobe beam width and low side lobes.\n\nWhile they both can give the same forward gain results the second antenna\nis obviously the better antenna.\n\nTo test for ground reflections raise and lower your antenna and also move it \nback and\nforward and see if your signal strength varies.\n\nOn a different day and different location repeat the measurements.\nYour results may well leave you wondering why you made the\nstatements you so confidently did.\n\nTo reduce ground reflections raise the antennas as far as possible above \nground.\nUse a high gain directional antenna for the signal source so that little of \nthe radiated\npower is directed at reflective surfaces.\nThe greater the spacing between the rx and tx antennas the more likelihood \nof\na reflection but the spacing needs to be such that a small change in spacing\nhas little effect on the results. As a rule of thumb spacing about 10 \nwavelengths.\n\nIn actual satellite operating a difference in forward gain of a db or less \nis hard\nto detect however the effects of the pattern can be significant in pointing \na hand\nheld antenna at a moving target.\n\nHaving made hundreds of comparison measurements on 13cm helix antennas\nI know how much time and effort it takes.  However I think it is very \nworthwhile\nto actually make real antenna comparison measurements to confirm the \ntheoretical.\n\nClare VE3NPC\n\n\n\n----- Original Message ----- \nFrom: \"John Kopala\" <[email protected]>\nTo: <[email protected]>\nSent: Sunday, April 24, 2011 11:49 PM\nSubject: [amsat-bb] Arrow and ELK Comparative Antenna Tests\n\n\n> On Saturday, April 23, Pat Stoddard (WD9EWK) and I did some antenna \n> testing in an attempt to answer\n> the questions about which is the best antenna for portable satellite \n> operation.  We only tested the\n> antennas in receive mode to determine their relative gain.  Time \n> constraints prevented us from\n> performing additional testing to determine if the transmitted output was \n> consistent with the receive\n> gain of the antennas.  For the time being we will assume (and we all know \n> the dangers of doing so)\n> that the transmit performance closely matches the receive performance.\n>\n> The antennas tested were an Arrow (3 x 7 elements), an ELK (4 elements), a \n> PortaFox configured for\n> 145/435 operation (4 elements), and a Home Brew 4 by 9 element \"arrow\" \n> antenna.  The standard Arrow\n> antenna was the only antenna equipped with duplexer, but not the basic \n> duplexer which is installed\n> in the handle.  We did not measure the insertion loss of the duplexer on \n> the Arrow antenna, but this\n> was obviously not a significant factor in the overall performance.  A \n> duplexer could still be\n> required depending upon the antenna chosen and the radio(s) to be used.\n>\n> Using the Arrow antenna as the reference antenna and 145.300 MHz as our \n> test frequency, our\n> measurements indicated that the Arrow and the ELK antennas had identical \n> gain.  The PortaFox antenna\n> showed 2db less gain than the Arrow and the ELK.  The Home Brew 4/9 \n> element crossed yagi showed 2db\n> more gain than the Arrow and the ELK.\n>\n> On 435.300 MHz, the Arrow antenna had 2db more gain than the ELK and 8db \n> more gain than the\n> PortaFox.  The Home Brew 4/9 element had 3db more gain than the Arrow.\nI \n\n",
    "attachments": []
}