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{ "url": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/email/Y7IH4WBBQMMLTBGZR7XORKPI4D5CY6E3/", "mailinglist": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/", "message_id": "20161020144852.Horde.awcC0UY7KBhyK7vGduli9lY@webmail.satavirtual.org", "message_id_hash": "Y7IH4WBBQMMLTBGZR7XORKPI4D5CY6E3", "thread": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/thread/6ANWKRMQC4HYMAREDVBEEAXR5JOWUDF2/", "sender": { "address": "pedro (a) dutrasousa.name", "mailman_id": "34c679918eec4d078abc3edf1f474373", "emails": "https://mailman.amsat.org/hyperkitty/api/sender/34c679918eec4d078abc3edf1f474373/emails/" }, "sender_name": "[email protected]", "subject": "Re: [amsat-bb] Crossed polarity dual band single feed yagi", "date": "2016-10-20T14:48:52Z", "parent": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/email/OIY4HYQWDYSTVHWKZNBVEGRELJIIMMCS/", "children": [ "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/email/36DF3LVTRX24P2CYWHZDD46JS5UJFSIZ/", "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/email/DPLAPGVF4NYFGP7VCZXOHCOX2OPDPELR/" ], "votes": { "likes": 0, "dislikes": 0, "status": "neutral" }, "content": "Hi Rico,\n\nThank you for that explanation.\n\nThe main problem here is that the original antenna has the UHF \nelements just to help the VHF tune into UHF. It's not a true dual feed \nVHF/UHF.\nSo if I get this concept in circular polarisation it'll always be for \nthe VHF leaving UHF to the mercy of a low gain.\n\nThe simulation confirms that the gain will bend into an elliptical \npolarisation, but not that significant.\n\nIt's tricky alright.\n\nHere are the calculations from 4nec2.\n\nhttps://dl.dropboxusercontent.com/u/6751494/single_VHF.png\nhttps://dl.dropboxusercontent.com/u/6751494/single_UHF.png\n\nhttps://dl.dropboxusercontent.com/u/6751494/3inch_VHF.png\nhttps://dl.dropboxusercontent.com/u/6751494/3inch_UHF.png\n\nhttps://dl.dropboxusercontent.com/u/6751494/16inch_VHF.png\nhttps://dl.dropboxusercontent.com/u/6751494/16inch_UHF.png\n\n73s Pedro\nCU2ZG\n\n\nQuoting Rico van Genugten <[email protected]>:\n\n> Hi Pedro,\n>\n> I have thought about this subject a lot. How to build an antenna that is\n> single boom, dual band, circularly polarized. I have come to the conclusion\n> that it is pretty difficult due to the following considerations:\n>\n> - To create a circularly polarized antenna a phase shift of 1/4 wl is\n> needed. A phase shift can be obtained through physical distance on the\n> boom, or a difference in feed line length.\n>\n> - When a phase shift of 0 is produced, for instance when the elements are\n> on the same location on the boom and there is no feed line difference, you\n> will end up with a diagonal linear polarized antenna. Think about it: You\n> have two perpendicular linear antennas in the same plane, the resultant\n> will be the summation of the two antennes: a diagonal antenna.\n>\n> - When a phase shift of anything in between 0 and 1/4 wl (or any multiple)\n> is produced, the antenna polarization is somewhere between linear and\n> circular: it will be elliptically polarized. This will mean that it is not\n> completely deaf in one plane like a linear antenna, but will have a gain\n> optimum in a particular plane and a gain minimum in a plane perpendicular\n> to it.\n>\n> - 1/4 wl spacing on UHF is (obviously) not the same as 1/4 wl spacing on\n> VHF, but if you use open-sleeve feeding (2 feed points) there is no way to\n> manipulate either the position on the boom or the feed line difference for\n> VHF and UHF independently\n>\n> - If you use 4 feed points you have full control of the placing of the four\n> antennas on the boom and the feed line differences and are probably able to\n> produce a true single boom, dual band, circularly polarized antenna, but\n> the VHF and UHF antennas will influence each other so strongly that you\n> will probably end up placing the UHF antenna after the last element of the\n> VHF antenna, leaving you with either a very long boom or very little gain.\n>\n> My two cents. :)\n>\n> 73, Rico\n> PA3RVG\n>\n>\n> On Thu, Oct 20, 2016 at 1:16 PM, Pedro via AMSAT-BB <[email protected]>\n> wrote:\n>\n>> Hi all,\n>>\n>> The best of ham radio is that you can build and experiment.\n>>\n>> My current portable yagi is a dualband single fed (VHF element) home\n>> built, from DK7ZB designs, 4+5 elements version. VHF has 9.25dB gain\n>> 1.03SWR, UHF 8.67dB 1.12SWR.\n>> It works like a charm.\n>>\n>> Now that I'm on the final stages of condo permits for a tower - although\n>> it's a tower on top of the building there are still space limitations - my\n>> goal is to build a crossed polarity set of my portable antenna. Something\n>> similar to what Gulf Alpha had, but instead of 4 feed points, one for each\n>> band/polarisation, I'll have only two, combined into one impedance matched\n>> feed line to the shack.\n>>\n>> Due to the required materials for the feed points and the elements\n>> positions I came up with 2 versions where the vertical antenna is ahead of\n>> the horizontal by 3 inches and 16 inches. My understanding is that circular\n>> polarisation would require a specific position for the vertical antenna\n>> plus the proper cable circuit for it.\n>> I'm aware that RHCP would give me a stable signal reception, rather than\n>> my setup even tilted 45 degrees instead of plain horizontal/vertical. I saw\n>> PU3GUO report on his VHF only antenna while receiving ANDE.\n>>\n>> I've ran the model in 4nec2 for the two options, 145MHz and 435MHz, and\n>> using 5W. Here are my findings.\n>>\n>> 3 inches separation:\n>>\n>> VHF\n>> Both antennas 1.03SWR\n>> Combined gain 9.25dB\n>>\n>> UHF\n>> Both antennas 1.12SWR\n>> Combined gain 8.67dB\n>>\n>> 16 inches separation:\n>>\n>> VHF\n>> Both antennas 1.03SWR\n>> Combined gain 9.24dB\n>>\n>> UHF\n>> Horizontal antenna 1.12SWR; Vertical antenna 1.49SWR\n>> Combined gain 8.27dB\n>>\n>>\n>> My conclusion is that advancing the vertical antenna by so many inches\n>> will result in interference from the horizontal one in such way that the\n>> gain is lower and SWR increases.\n>> Gain in UHF is lower, expected as same happens in my current portable\n>> antenna, and that's because it's being fed in the VHF element.\n>>\n>> Has anyone built something similar that can share any comments?\n>> Would there be any other configuration possible for a single boom?\n>>\n>> Thanks in advance.\n>>\n>> 73s de Pedro\n>> CU2ZG, HM77\n>>\n>>\n>>\n>> --\n>> This message has been scanned for viruses and\n>> dangerous content by MailScanner, and is\n>> believed to be clean.\n>>\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>\n> --\n> This message has been scanned for viruses and\n> dangerous content by MailScanner, and is\n> believed to be clean.\n\n\n\n\n-- \nThis message has been scanned for viruses and\ndangerous content by MailScanner, and is\nbelieved to be clean.\n\n", "attachments": [] }
