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Thread: Crosshair - 10 dbic Circularly polarized antenna tutorial!

  1. #991
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    Dumb question for reflector size..

    I got a question..

    Am I stuck to use either a small reflector or a large reflector?? Am I correct in assuming that I can pick a number between 8800 and 17500..?

    Is there a preferable size reflector to use with 900 Mhz..?
    Last edited by Mykro; 18th July 2013 at 10:15 PM.

  2. #992
    Engineer for Jesus Christ IBCrazy's Avatar
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    The larger the reflector, the higher the gain and the better the F/B ratio will be. For a stand alone antenna the you do not intend to fly behind at all, larger is better. If you do intend to fly behind it frequently, a smaller reflector is better.

    -Alex
    If it is broken, fix it. if it isn't broken, I'll soon fix that.

    videoaerialsystems.com - Performance video piloting

  3. #993
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    Alex, I've got a galvalume metal sheet (Steel sheet coated with a compound that is 43,5% zinc, 55,0% aluminium and 1.5% silicon). Will it work? I'm worried about it because it is very difficult do solder...
    Last edited by thiagokern; 19th July 2013 at 11:01 AM.

  4. #994
    Engineer for Jesus Christ IBCrazy's Avatar
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    If you can solder it, it will work.
    If it is broken, fix it. if it isn't broken, I'll soon fix that.

    videoaerialsystems.com - Performance video piloting

  5. #995
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    Alex,

    Two questions for you...

    Is it critical that the top of the Balun tube be more than a 1/16th of an inch lower than the eighth of the element??. In post #3 You said.." The measurement from the top of the tube to the base of the reflector should be about 1/16” less than your height so your elements can clear it." If you look at the pics in post #4 the top of the tube looks to be lower than a 1/16" .. It looks as though 3/16" to a 1/4" lower than the height of the element.. Can I safely assume it's not that critical..?? I haven't cut my Balun tube yet to the measurement the formulas states.. Just want to be sure first..

    Also.. (See pic).. I have some L-com White 195RW coax lying around that I want to use.. (It is 50ohm) My question is: The outer insulation is a bit thicker which takes up more room inside the 3/8" tube that I'm using.. You said it needs air around the cable to work decent, would there be enough of air insulation around this cable..?? Is this cable ok to use??.. Or should I go with 1/2" tube..??
    Has anyone used this cable with good results..??

    Click image for larger version. 

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    Thanks

    Michael
    Last edited by Mykro; 20th July 2013 at 07:50 PM.

  6. #996
    Engineer for Jesus Christ IBCrazy's Avatar
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    Michael,

    Good questions. Very good questions. Here's my suggestions:

    1. Strip the insulation from your cable shield and tin it with a soldering iron. Maybe 1 wrap of packing tape or something to insulate it. This will make the balun work better.

    2. height isn't that critical but you should be fairly close. Closer is better, but maintaining 1/16" is unnecessary.

    -Alex
    If it is broken, fix it. if it isn't broken, I'll soon fix that.

    videoaerialsystems.com - Performance video piloting

  7. #997
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    Thanks Alex..

    I'm going to re-insulate the shield with a super thin coat of Goop..

    Michael

  8. #998
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    Crosshair Completed...

    Ok.. Here is my first ever Crosshair..


    Click image for larger version. 

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    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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    Last edited by Mykro; 21st July 2013 at 02:08 PM.

  9. #999
    Engineer for Jesus Christ IBCrazy's Avatar
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    ^That looks awesome to me. Wait until you fly it

    -Alex
    If it is broken, fix it. if it isn't broken, I'll soon fix that.

    videoaerialsystems.com - Performance video piloting

  10. #1000
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    Redid my elements last week after they were bent, and wow I must have done something right as the beam width seems wider and picture is more solid at distance than before!

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