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{
    "url": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/email/F7Q6Q6ELORLWB22RMBYN7BFF5P7U7K4C/",
    "mailinglist": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/",
    "message_id": "CAJdc4v4qROMJHPo8ykWFs-jArmjKdVQsS6u+F7M3XixGZGF0fA@mail.gmail.com",
    "message_id_hash": "F7Q6Q6ELORLWB22RMBYN7BFF5P7U7K4C",
    "thread": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/thread/H2RM3X7RB6XXKTQZETG734H2S25BPC7T/",
    "sender": {
        "address": "rico.van.genugten (a) gmail.com",
        "mailman_id": "64397f008c1d4d7a8656e4f690b21e7f",
        "emails": "https://mailman.amsat.org/hyperkitty/api/sender/64397f008c1d4d7a8656e4f690b21e7f/emails/"
    },
    "sender_name": "Rico van Genugten",
    "subject": "Re: [amsat-bb] Egg beater antenna",
    "date": "2016-03-16T09:04:20Z",
    "parent": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/email/H2RM3X7RB6XXKTQZETG734H2S25BPC7T/",
    "children": [],
    "votes": {
        "likes": 0,
        "dislikes": 0,
        "status": "neutral"
    },
    "content": "Hi Guys,\n\nThe main problem I'm having with omni antennas for sat work is the mounting\nheight. In short, this is the dilemma:\n - Mount it too low: horizon is obstructed badly\n - Mount it too high: antenna radiation pattern is distorted badly\n\nIn a lot of simulations you find online the ground systems of omni antennas\n(radials, screen, you name it) are modeled in the same plane as the earth\nsurface, simulating a situation where the antenna is mounted very low. Or\nworse: the antenna is modeled over perfect earth, as if the ground system\nwas solid, perfectly conducting and infinite in size (could be a good\napproximation at sea, but definitely not in a typical home situation). To\nsimulate a more realistic situation I modeled the ground system (radials)\nat the actual mounting height above the earth surface, with the radiating\nelements above it.\n\nIn my case the antenna would be mounted at about 10 meters (33 feet) height\nto get a clear view of the horizon. What I see when I simulate that\nsituation is that the ground system (radials) on an eggbeater works\nperfectly to fix the near field of the antenna, i.e. to get a nice SWR and\neven push the radiation pattern upwards, but it does little about the far\nfield of the antenna. What you typically see when you mount a (partially)\nhorizontally polarized omni at several times the wavelengths above earth,\nyou get very deep peaks and throughs varying with elevation. This is\nbecause the signal arrives via several paths: it arrives directly, but also\nvia earth reflections. This results in constructive or destructive\ninterference depending on the elevation angle. This can be clearly observed\nin this eggbeater simulation:\n\nEggbeater at 10m: http://postimg.org/image/p973lofrz/\n\nOther (partially) horizontal omni's show the same effect. For example this\nis a Lindenblad as I have built (EZ Lindenblad design by Tony Monteiro\nAA2TX):\n\nLindenblad at 10m: http://postimg.org/image/rrssmd1i7/\n\nOf course these simulations don't take into account that the antenna isn't\nmounted in free space but that there are buildings, trees, etc. nearby, but\nthe effect was pretty pronounced when I was testing my Lindenblad at about\n10m height at a recent ARISS contact, notice the sharp signal drops every\nnow and then. This is not caused by polarization mismatch since a\nLindenblad is cross polarized for every elevation angle, unlike an\neggbeater which becomes horizontal near the horizon.\n\nContact: https://www.youtube.com/watch?v=6H6lqluWLwc\nAntenna situation:\nhttps://twitter.com/tete_de_moine/status/706085371873005569\n\nFor uplink this is not a problem, since even with 5 watts the uplink power\nis usually orders of magnitude bigger than the downlink power and I don't\nreally notice the peaks and throughs. But on downlink this could really be\na dealbreaker on difficult QSO's, but of course as always, ymmv. The amount\nof peaks and throughs increases as you mount the antenna higher, so if you\nare able to mount the antenna very low and still see the horizon this might\nnot be an issue.\n\nNow I'm wondering, would you see the same effect with a yagi when it is\nmounted at several wavelengths height and pointed to the horizon?\nEspecially near sea this effect should be pretty pronounced. Did anyone\never experience this? Maybe I should spend some simulation time on this..\n\n73,\nRico PA3RVG\n\n\n\nOn Wed, Mar 16, 2016 at 1:13 AM, Dick Illman <[email protected]> wrote:\n\n> I have successfully used UHF and VHF Egg Beaters in my attic for years. I\n> used a TS2000 and ARR transceiver preamps (TS2000 is pretty deaf). I had\n> 100 feet of 9913 cable.\n>\n> 73 Dick Illman\n> AH6EZ/W7\n> _______________________________________________\n> Sent via [email protected]. AMSAT-NA makes this open forum available\n> to all interested persons worldwide without requiring membership. Opinions\n> expressed\n> are solely those of the author, and do not reflect the official views of\n> AMSAT-NA.\n> Not an AMSAT-NA member? Join now to support the amateur satellite program!\n> Subscription settings: http://www.amsat.org/mailman/listinfo/amsat-bb\n>\n",
    "attachments": []
}