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{
    "url": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/email/NP7S23ILARR6MYWPXDO3HE5ZZKF4LZJD/?format=api",
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    "message_id": "003b01c71a21$9deebbe0$6401a8c0@DBXPPPOR",
    "message_id_hash": "NP7S23ILARR6MYWPXDO3HE5ZZKF4LZJD",
    "thread": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/thread/XDHPZGDMMB6N2ESXZKYVS5DH24WGBZEQ/?format=api",
    "sender": {
        "address": "david.barber (a) dbelectronics.co.uk",
        "mailman_id": "d692dab59bc14b8f8772165690245987",
        "emails": "https://mailman.amsat.org/hyperkitty/api/sender/d692dab59bc14b8f8772165690245987/emails/?format=api"
    },
    "sender_name": "David Barber",
    "subject": "[amsat-bb] Re: Beginer Antenna Selection",
    "date": "2006-12-07T17:03:26Z",
    "parent": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/email/XDHPZGDMMB6N2ESXZKYVS5DH24WGBZEQ/?format=api",
    "children": [],
    "votes": {
        "likes": 0,
        "dislikes": 0,
        "status": "neutral"
    },
    "content": "Hi Steve\n\nI would echo the \"simplicity\" vein in Bruce's words.\n\nI recently worked him and W1FC via FO-29 from my location north east of\nLondon, England using a tri-band co-linear at about 30ft, no pre-amps, a\nDiamond Tri-Plexer and 45W out of the rig, a TS2000.  Location is 30ft asl.\n\nNot great copy but we made the contact and that's part of the fun!\n\nRegards\n\nDavid\nG8OQW\n\n\n-----Original Message-----\nFrom: [email protected] [mailto:[email protected]] On\nBehalf Of Bruce Robertson\nSent: 07 December 2006 16:08\nTo: [email protected]\nCc: [email protected]\nSubject: [amsat-bb] Re: Beginer Antenna Selection\n\n\n\nQuoting Steve Raas <[email protected]>:\n\n> Well here is my 1st question.\n> \n>  \n> \n> In researching what is needed for working sat's , I have found that I\n> am\n> looking for an antenna that has RHCP, although selectable RHCP & LHCP\n> is\n> avail.. I just cannot justify the added expense for a 5% probability of\n> an\n> improved signal. \n\nSteve:\n\nWhat an excellent question! My answers and advice below are based on some\nexperience and on reading this list for the last couple of years. I hope\nthose who are more knowledgeable will correct any errors.\n\nAntenna selection is partly determined by your rotation scheme. If you are\nusing azimuth rotation alone, which I and many others would recommend and\nyou suggest below, the following advice pertains.\n\nI would strongly recommend against *any* circular polarization to start.\nUse a linearly polarized antenna of modest length instead. If you do get a\ncircularly polarized ones for 2m and 70cm, they should have switchable\npolarization. This is because different birds use different polarization\nfor their antenna array, and in LEO they can end up reversing polarization.\n\nHowever, adding switchable circ. polarization adds enormously to the cost\nof the array or, in the case of homebrew, to the risk of muddling the thing\nup. \n\n> \n> That being said.. Are 'Typical' terrestrial SSB Yagis  RHCP?  I am\n> looking\n> at the following antennas for known performance vs. price:\n\nNo, they're not. Yagis can produce circularly polarized signals if two of\nthem at right angles are fed in proper phase. Thus, a yagi-like antenna\nthat is circularly polarized will look like a combined vertically-oriented\nand horizontally-oriented yagi. \n\n> \n> 2m -  DPM144-5LVA  (http://www.directivesystems.com/lva.htm)\n\n\n> \n> 430-440 - DSFO432-15RS (http://www.directivesystems.com/DSFO432-15.htm)\n\nTuning on this band can be very touchy. If it says it is for 432, I'd give\nit a pass: you're going to be up at 435 MHz. \n \n> \n> You may wonder why I'm looking @ such small antennas and I will answer\n> that\n> My main coaxial run from rig to preamp may be at most 30'.  \n\nThese are not small antennas for LEO work. They are, in fact, too large if\nyou are planning to use an azimuth-only rotation setup, which is really all\nyou need (esp. with preamps on the mast). I'd go much, much smaller.\n\nAs a sort of point of comparison, I'm upgrading from homebrew 8-el on 70cm\nand 4 el on 144 with fixed elevation (az-only) only in order to work the\nbottom 5 degrees of elevation and DX into W. Europe. That modest setup has\ngarnered me hundreds of contacts and a world of fun. Like many on this\nlist, I used the WA5VJB 'Cheap Yagi' design. It works. A recent pdf is at:\nhttp://portal.ucpel.tche.br/py3vhq/home/antenas/uhf-sw.pdf\n\nMy guess is that any commercially-built array will be much more than the\ncost of a 2m/70cm SWR meter (you can even use a FT-817 as a poor-man's\nversion!) plus the materials needed for a Cheap Yagi array. You might try\nsome of the other designs that people have had success with, such as the\nTexas Potato Masher II.\n\nAll of these are predicated on the fact that a longer boom yagi will make\nyour (fixed az.) station *less* fun to work with. Greater gain comes at the\ncost of a narrower beamwidth, both vertically and horizontally. You'll\ntherefore find worse nulls as the bird goes overhead, and you'll find the\nadjustment of the az. rotor will be unpleasantly touchy. \n\nThere is a long-running debate about the optimal gain pattern for fixed\nel., but I'd say my 4-el. 2m antenna has a shade too little directionality\nfor my liking. Still, I've used it for over a year now. The 70cm antenna is\na champion in my books.\n\nI'm\n> probabaly\n> going to feed them both with an LMR-400 type cable, possibly LMR-600 on\n> UHF\n> but with such a short run and loss under 1.0db I don't know nor have\n> decided\n> if it would be worth it. Also I plan on mounting these ( or similar\n> yagis )\n> @ a 30deg angle with a simple rotor as an AZ/EL rotor is not an option\n> at\n> this moment due to cost. So to sup up my initial statement I don't need\n> another 3dB of gain to make up for line loss, So in theory I can keep\n> the\n> antennas smaller.\n\n30 deg. is pretty high, even with the short yagis (brutally so with long\nones). Unless you will not get a signal to the lower elevations, due to\nfoliage, houses, etc., I would experiment with 10 deg. to 20 deg.\n\nYou've probably read that you need to put together the 'best receiving\nstation you can'. You may also, as I did, fear that people will label you\nan alligator if you can't hear very well. In practice, folks on the birds\nare very understanding if you use modest power and are beginning. What's\nfrustrating are the people who have been around for ages, put booming\nsignals into the bird and don't seem to be able to hear anything but a\nsignal equally booming. Because one can hear one's own signals, the problem\nis quite obvious to others. \n\nA last thought, which doesn't respond to your questions, but might be as\nmuch fun for you as it was for me: one of my first satellite antennas was a\n70cm 1/4w groundplane. I just soldered some house hookup wire to a bnc\nconnector: two for a groundplane, one for a vertical element. With a 6' run\nof RG-58 and a wooden roof, I can hear many birds in CW mode: LO-19\n(booming!), the FM of AO-51 (listening in CW mode), GO-32. No rotating, no\nnothing. Granted, in my experience such an antenna doesn't quite suffice\nfor two-way communication. But it reduces the number of variables in\nsetting up a computer-aided station, if that's the way you want to go, and\nAOS prediction in any case.   It is so cool to just listen to the bird come\nup, explore the elevation at which it is heard, listen to fading patterns,\nand observe doppler. Recreate the OSCAR 1 experience in about 5 minutes of\nantenna building!\n\nLater on, when something goes wrong with your outdoor array, you can always\ngo back to this antenna as a baseline. In fact, when I lost my 70cm antenna\nto moisture in the feedline, I used this antenna a) to confirm the problem;\nb) to transmit up to VO-52! It's also a great way of testing an unknown\nreceiver on 70cm: if LO-19 doesn't come in LOUD with the 1/4w groundplane,\n I'd say that receiver is useless for LEO work. \n\nSimilarly, a three-element yagi on 2m will do a great job of picking up\nVO-52. I lashed one together, and pointed it by hand within my wood-frame\nhouse. Not  R5 copy, mind you, but great fun and cheap. It will even copy\nAO-7.\n\n73, Bruce VE9QRP\n----- End forwarded message -----\n\n\n-- \nBruce Robertson, \nDept. of Classics, Mount Allison University\nhttp://heml.mta.ca\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",
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