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{ "url": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/email/B5YEHMQKGNQHUZCNWI5L6BINFJERIR6G/?format=api", "mailinglist": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/?format=api", "message_id": "[email protected]", "message_id_hash": "B5YEHMQKGNQHUZCNWI5L6BINFJERIR6G", "thread": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/thread/6VKSY2YUOJBL374MDTP74B2LXFYTBD44/?format=api", "sender": { "address": "wa5vjb (a) flash.net", "mailman_id": "542e9d070f55492f953bc190bd8cff2d", "emails": "https://mailman.amsat.org/hyperkitty/api/sender/542e9d070f55492f953bc190bd8cff2d/emails/?format=api" }, "sender_name": "KENT BRITAIN", "subject": "[AMSAT-BB] Helix for 1.2/2.4 GHz", "date": "2021-02-28T21:02:18Z", "parent": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/email/ZNASKAJ7X4CIWWTTVT7ZQOGXH2FVUED2/?format=api", "children": [ "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/email/HCQZOC2XXHBIODR26RVMQGEI53XFAXAU/?format=api", "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/email/2IOCSGZSQQL44M7X4537HYJVO42JJGKP/?format=api" ], "votes": { "likes": 0, "dislikes": 0, "status": "neutral" }, "content": " Hi Jerry\nI have taken an antenna range to over 60 conferences. And done quite a bit or work with Helix antennas at my lab. Of the 100 or so Helix's I have tested, only about 10% were circularly polarized.That's right, only about 1 in 10. I have proven many many times, HAMS CANNOT BUILD CP HELIX ANTENNAS! It is amazing how a Helix Antenna can have an Axial Ratio of over 20 dB. That's about the same axial ratio as you get from many Yagi's. The few helix's that worked were usually built by a professional in the field.\nUnless you have actually tested your Helix on a range, the chances are about 9 out of 10 is it not CP(Yes, it is a valid statement that all antennas are ellipticaly polarized, CP and Linear are just special cases.).\nAs an example, the wave comes down the helix, hits the tip, them reflects as a standing wave on the helix structure with an opposite CP sense.You can put a helix antenna on an antenna range, then start trimming the tip with some wire cutters a few millimeters at a time. The Axial ratio will be constantly changing. You can, with some experimenting, find the CP point, but statistics are against you without any testing. \nAnd the Kraus Formulas are about 3 dB Optmistic.\nWinding the helix on a plastic pipe creates all sorts of problems. In free space the radio wave travels along the wire at about 95% the speed of light. When you wrap the wire on a plastic tube, the velocity factor is now about 60%.The effective length and turns ratio is completely different from the calculations. And darn near impossible to even simulate What is the dielectric constant of that plastic you got at the hardware store? And If you did look up the Er, that value was measured at 1kHz, not 1269 MHz! So unless you actually measured the Er at 1269 MHz, your CST, HFSS, OPENEMS, etc simulation is not valid.\nSam, G4DDK was the first to measure the effects of using just one dielectric boom with the helix winds attached directly to the boom. i.e. one boom and the helix turns attached to the boom at their 12 O'clock position.The dielectric effects of the boom tilts the beam in the direction of the boom.and really reduces the gain of long helix antenna. \nThe NASA way, central boom and spokes to support the helix is by far the best way to go.\n73 Kent WA5VJB\n\n On Sunday, February 28, 2021, 01:39:25 PM CST, <[email protected]> wrote: \n \n Build one myself for 23cm years ago on 1268Mc. 2*19el fixed RHCP. The tricky part was the DR environment because spacings are small on 23cm.\nMade it with 1/4L mechanical spacing. It never lead me dwn, worked beter then my 30t helix.\nI hope my 4pol switch for this crossyagi will be finished in a month or 2, but busy with building µwave EME setup.\nMaybe i will try it first with my 70cm 4pol switch, but this will have more loss. \n\nI've never seen commercial crossyagis for 23, but WIMO used to have helix antennes for 23c,and 13cm, or try to make them yourself.\n\nbest 73's\n\nJerry,ON4CJQ\n\n----- Oorspronkelijk bericht -----\nVan: \"amsat-bb\" <[email protected]>\nAan: \"amsat-bb\" <[email protected]>\nVerzonden: Zondag 28 februari 2021 11:41:35\nOnderwerp: [AMSAT-BB] WTB: Circular Polarized Yagis for 1.2/2.4 GHz\n\nTrying to locate a good source for these. M2 doesn't have these. Ideas pls?\n\n73/Ed NI6S\n\n-----------------------------------------------------------\n\nSent via AMSAT-BB(a)amsat.org. AMSAT-NA makes this open forum available\nto all interested persons worldwide without requiring membership. Opinions expressed\nare solely those of the author, and do not reflect the official views of AMSAT-NA.\nNot an AMSAT-NA member? Join now to support the amateur satellite program!\n\nView archives of this mailing list at\nhttps://mailman.amsat.org/hyperkitty/list/[email protected]\nTo unsubscribe send an email to amsat-bb-leave(a)amsat.org\nManage all of your AMSAT-NA mailing list preferences at https://mailman.amsat.org\n\n-----------------------------------------------------------\n\nSent via AMSAT-BB(a)amsat.org. AMSAT-NA makes this open forum available\nto all interested persons worldwide without requiring membership. Opinions expressed\nare solely those of the author, and do not reflect the official views of AMSAT-NA.\nNot an AMSAT-NA member? Join now to support the amateur satellite program!\n\nView archives of this mailing list at\nhttps://mailman.amsat.org/hyperkitty/list/[email protected]\nTo unsubscribe send an email to amsat-bb-leave(a)amsat.org\nManage all of your AMSAT-NA mailing list preferences at https://mailman.amsat.org \n\n\n", "attachments": [ { "email": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/email/B5YEHMQKGNQHUZCNWI5L6BINFJERIR6G/?format=api", "counter": 2, "name": "attachment.html", "content_type": "text/html", "encoding": "utf-8", "size": 7826, "download": "https://mailman.amsat.org/hyperkitty/list/[email protected]/message/B5YEHMQKGNQHUZCNWI5L6BINFJERIR6G/attachment/2/attachment.html" } ] }