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{
    "url": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/email/U7FQQLWTIE6JAZMWHM3WAADFGXSAMDOD/?format=api",
    "mailinglist": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/?format=api",
    "message_id": "[email protected]",
    "message_id_hash": "U7FQQLWTIE6JAZMWHM3WAADFGXSAMDOD",
    "thread": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/thread/44OSNNSFKT5S6MFEHZ6FGN4LIJ7KHK53/?format=api",
    "sender": {
        "address": "zleffke (a) vt.edu",
        "mailman_id": "57a24afb1cf641f98121841e6753c12e",
        "emails": "https://mailman.amsat.org/hyperkitty/api/sender/57a24afb1cf641f98121841e6753c12e/emails/?format=api"
    },
    "sender_name": "Zach Leffke",
    "subject": "Re: [amsat-bb] Linear vs Circular Polarization",
    "date": "2017-04-12T23:28:19Z",
    "parent": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/email/44OSNNSFKT5S6MFEHZ6FGN4LIJ7KHK53/?format=api",
    "children": [],
    "votes": {
        "likes": 0,
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        "status": "neutral"
    },
    "content": "Hi Brady,\n\nMy quick three cents:\n\nfirst penny)  The coax relay at the feedpoint method is feasible and is \nhow the M2 Antennas Inc. switchable polarization sense feedpoints work.  \nI have no personal experience fabricating these, but we use them in the \nVT Ground station to switch between LHCP/RHCP.  M2 Antennas \ndocumentation warns of a slight VSWR increase with this technique, but \nso far (couple years now) they have performed great for us.\n\nsecond penny)  While you might not have to cut phasing lines with the \n1/4 wave offset technique, you will likely need to cut 1/4 wave \nimpedance transformation lines.  If your two feedpoints are 50 ohms \neach, then a 1/4 wave transformer of 75 coax will be needed \n(transforming to 100 Ohms) so that when they are placed in parallel (via \na splitter/combiner) you present 50 ohms to the feedline/radio.  This \nlink has a lot of good info on this:\n\nhttp://www.qsl.net/sv1bsx/antenna-pol/polarization.html\n\n\nthird penny)  There is a great section in the ARRL Antenna Book (I think \nin the Antennas for Space Communications chapter) about using a coax \nrelay and a pair of 50 ohm feedpoint yagis to achieve circular \npolarization.  The coax used in that example is both for phasing and \nimpedance transformation in one, though requires 100 ohm (or close to \nthat) coax (which last time I checked was available at the RF \nconnection, who can also fabricate properly phase calibrated cables for \nyou).  Also the relay in that example was not at the feedpoint of the \nantenna.  So it does exactly the opposite of what you are trying to do \n(antennas are not offset, and you need phasing/impedance transformation \nlines) but in my experience I found it easier than trying to crack open \na (potentially expensive) coax relay and integrate it into a feedpoint \n(I left that to the pros at M2 Antennas).\n\n\nGood Luck!\n\n\n73s,\n\nZach, KJ4QLP\n\nResearch Associate\nAerospace Systems Lab\nTed & Karyn Hume Center for National Security & Technology\nVirginia Polytechnic Institute & State University\nWork Phone: 540-231-4174\nCell Phone: 540-808-6305\n\nOn 4/12/2017 6:51 PM, Richard Tejera wrote:\n> Brady,\n>\n> Domenici, I8cvs SK had published a pair of articles on making a switching relay between vertical, Horizontal, LHCP & RHCP. he sent me PDF's, which are in my to do someday folder.\n>\n> Contact me off list (email is good on QRZ), and I will send them to you. They are for 70cm, but certainly can be adapted for 2m easily enough.\n>\n> Rick Tejera K7TEJ\n> Saguaro Astronomy Club\n> www.SaguaroAstro.org\n> Thunderbird Amateur Radio Club\n> www.w7tbc.org\n>\n> On April 12, 2017, at 14:11, Brady Gordon <[email protected]> wrote:\n>\n> Hi Everyone,\n>\n> I'm working on building a pair of crossed yagis for 2m and 70cm, and I have\n> some questions.  I apologize if this has been discussed before, but I\n> couldn't find answers online so I was hoping you all could help me out.\n>\n> First, it seems easiest to me to build an antenna system that can either\n> switch between vertical and horizontal linear polarizations, or between\n> right hand and left hand circular polarization.  Which would be more\n> useful?  And is it worth the extra effort to build an antenna system that\n> can switch between all four polarizations?\n>\n> Also, I've been looking at the different ways of achieving circular\n> polarization.  I like the idea of using mechanical 1/4 wave separation\n> between the two yagis so I don't have to cut phasing lines.  Would it be\n> possible to switch polarizations by putting a relay at the feedpoint of one\n> of the yagis and switching which side of the driven element the center\n> conductor and shield of the coax goes to?  I've never seen this done\n> before, but it seems to me it would work.  Any thoughts?\n>\n> Thanks and 73,\n> Brady AC0XR\n> _______________________________________________\n> Sent via [email protected]. AMSAT-NA makes this open forum available\n> to all interested persons worldwide without requiring membership. Opinions expressed\n> are solely those of the author, and do not reflect the official views of 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> Sent via [email protected]. AMSAT-NA makes this open forum available\n> to all interested persons worldwide without requiring membership. Opinions expressed\n> are solely those of the author, and do not reflect the official views of 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",
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