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{
    "url": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/email/U24EU75PHSIUNUMRS7XEBOGFETRLYJNQ/",
    "mailinglist": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/",
    "message_id": "[email protected]",
    "message_id_hash": "U24EU75PHSIUNUMRS7XEBOGFETRLYJNQ",
    "thread": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/thread/U24EU75PHSIUNUMRS7XEBOGFETRLYJNQ/",
    "sender": {
        "address": "hamoen (a) iae.nl",
        "mailman_id": null,
        "emails": null
    },
    "sender_name": "Henk, PA3GUO",
    "subject": "[amsat-bb] Re: AOP-1 Polarity Switch",
    "date": "2008-10-25T07:49:46Z",
    "parent": null,
    "children": [],
    "votes": {
        "likes": 0,
        "dislikes": 0,
        "status": "neutral"
    },
    "content": "> I realize this is a long shot, but...am looking for a PS-4\n> polarity switch that was used with the 416-TB, 70CM,\n> antenna. Any information about this switch would really be appreciated.   Tks\n> Bruce   KEØLX\n\nHi Bruce !\n   Can't help you with the original PS-4 unfortunately, but ..\n   I just finished documenting what I did in the past 3 weeks with my 416TB.\n   See http://www.pa3guo.com (click on ANTENNAS, click on Cuchcraft 416TB).\nHenk\n\n\"Modification of the Cushcraft 416TB (2x8 elements) 70cm antenna\"\n(add switchable circular polarization)\n\nIntroduction\nCushcraft provided with the 416TB antenna a polarization 'phasing harnesss'\nthat allows either fixed LHCP or RHCP. For years I used RHCP and was fully\nsatified with the performance (AO51, VO52, FO29, Cute-II, ...) Click here\nfor the original Cushcraft 416TB Manual (pdf):\nhttp://www.pa3guo.com/cushcraft_416tb_manual.pdf\n\nBelow a picture of the harness as I had it mounted (fixed RHCP) for years:\nhttp://www.pa3guo.com/cushcraft_416tb_original.jpg\n\nWith AO51's 435.150 MHz downlink I had an issue as that applies LHCP.\nI could clearly notice the signal strength difference between 435.300\n(RHCP, strong) and 435.150 (LHCP, hardly audible). Then when AO51 started\nto apply repeater modes on 435.150 as well, which I now was starting to\nmiss out on, I wanted to be able to switch between LHCP and RHCP.\n\nDesign\nAs I had only one relay available (these projects alway start on Sundays\nwhen shops are closed), the option of HOR/VER/LHCP/RHCP was dropped and\nonly switching between LHCP/RHCP remained.\n\n>From various sources on the internet and an article of Domenico Marini,\nI8CVS, (\"Switching four Polarizations on a 70cm Crossed Yagi\", AMSAT\nJournal May/June 2007) I derived the set-up needed for the Cushcraft 416TB,\nwhich has both antennas at 1/4 lambda distance separated from eachother\n(A - B in the diagram below):\nhttp://www.pa3guo.com/cushcraft_416tb_pol_system.jpg\n\nThe original Cushcraft harness basically consisted of Z1 and Z2 only, and\nRCHP vs LHCP was selected by swapping the conductor & shielding at the feedpoint\nof the front dipole.\n\nIn the new above set-up, LHCP is obtained when the relay is excited\n(signal travels through Y2), else the resulting polarization is RHCP.\n\nZ1 and Z2 form the impedance transformers, which transform the 50 ohm of each\ndipol into 100 ohm, which are then connected in parallel resulting in 50 ohm.\nY2 is the phase shifter: if enabled the signal from/to the front dipol is\nshifted 180 degrees (1.2 wave).\n\nImplementation\nFor Z1 and Z2 I used RG59B/U (75 ohm): V=0.66: ((300/435)*0.66)/4= 11.4cm.\nX1 and X2 just need to be identical in length, I have used 40 cm Aircell (50 ohm).\nu1 and u2 need to be identical in length, u2 is a small piece of copperwire between the relay pins (~4mm).\nY1 needs to be 1/2 wave longer as u2, I used Aircell (50ohm): V=0.83: (((300/435)*0.83)/2)+4mm= 29.0cm\n\nU1 is created by soldering the conductors of the two coax cables directly\ntogether and putting a closed copper shielding around that (by soldering the\nshieldings/braids of the two coax cables together and around the conductor)\nto form again a shielding. Refer to point 'u1' in the picture of the box below.\n\nDomenico Marini advices in his article to use proper coax relay and in general\ndescribes a more perfect system, including HOR/VER/LHCP/RHCP options. I have\nchosen a much cheaper and simpler implementation, which is most likely also\nless accurate. So for those that want to built this system as well, I recomment\nthem to read the article of Domenico first and decide themselves how to built.\nDo not only refer to my implementation described here.\n\nI have used a simple SDS S2-12V relay, which is expected to work up to 450 MHz.\nKey is to keep all wires as short as possible. All coax braids (shieldings) have\nto be soldered together via the shortest possible way. See the yellow circle in the\npicture of the box. Parallel to the relay I have mounted an LED, which makes it\neasy to be able to see without a voltage meter (eg outside standing at the roof)\nif the 12V is present in the box or not:\nhttp://www.pa3guo.com/pol_switch.jpg\n\nAgain: using a real coax relay would have been much better. Using a waterproof\nmetal box instead of my plastic one would have been better as well, but I didn't\nhave one and it would have made the construction much heavier. But as I am not\naiming for an EME station I decided to give this implementation a try.\n\nFirst I stripped the antenna and removed the original phasing harness:\nhttp://www.pa3guo.com/cushcraft_416tb_stripped.jpg\n\nThe baluns are carefully removed and cleaned as I needed them also in the new set-up:\nhttp://www.pa3guo.com/cushcraft_416tb_balun.jpg\n\nNext the actual switch was made and placed in a 220V outdoor box (waterproof) and mounted in the tower:\nhttp://www.pa3guo.com/cushcraft_416tb_switch_a.jpg\nhttp://www.pa3guo.com/cushcraft_416tb_finished.jpg\n\nResults\nJust comparing the 435.150 and 435.300 downlinks of AO51 I concluded the system works:\n- In the past I could not hear the 435.150 downlink. Now I can; by selecting the correct polarization.\n- Signal strength of the 435.300 downlink has not decreased compared to the past (the fixed Cushcraft harness).\n\nConclusions\nWith a few pieces of coax, a waterproof housing and a relay a Cushcraft 416TB\ncan be upgraded from fixed Circular Polarization (CP) to (remote) switchable\nLeft or Right Hand Circular Polarization (LHCP or RHCP).\n\nImplementation has been done using spare parts as I needed LHCP/RHCP to become\navailable quickly. However, a next time, instead of a normal relay, I will use\na coax relay as it is expected to give better mechanical stability and improved\nRF performance.\n\nHenk, PA3GUO\nhttp://www.pa3guo.com\nOctober 2008\n\n\n\n\n",
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}