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Thread: Tune your 1.2/1.3GHz patch to the proper resonance

  1. #1
    Engineer for Jesus Christ IBCrazy's Avatar
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    Tune your 1.2/1.3GHz patch to the proper resonance

    Thanks to sim io for sending me his 1.3 GHz patch, we now know that the 1.3GHz L-com patch (part# AN1308) is utter garbage. SWR of 6:1! Come on now, that's awful!

    So how do we fix this? Well, it's not easy, but it's not hard either

    In this thread, I'll show you how to tune you patch to whatever frequency you like

    -Alex
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    Last edited by IBCrazy; 5th March 2011 at 10:32 AM.

  2. #2
    Engineer for Jesus Christ IBCrazy's Avatar
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    I tested the resonance at 1160 MHz, a far cry from the 1280 that it was supposed to be. Luckily antennas scale really well. What does this mean? This means you follow the equation:

    Tuned dimensions = (old dimensions * old frequency)/Your frequency

    The element was measured at 4.5"X 4.75"

    Plugging the numbers into the formula and solving we get the new dimensions as such: 4.02X4.25"

    So now we have to get the thing apart, trim it, and glue it back together.

    -Alex

  3. #3
    Engineer for Jesus Christ IBCrazy's Avatar
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    Opening the antenna

    Opening the antenna is no easy task. I used a flathead screwdriver into the side of the patch. Forget about the corners, they're not coming up.

    Pry gently along the edge as you pull the antenna apart. Be careful not to bend the ground plane.

    -Alex
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  4. #4
    Engineer for Jesus Christ IBCrazy's Avatar
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    Now it's time to trim down that top plate. I used a set of tin snips. Aviation snips will do ok. If you have some really strong scissors, those might work.

    I needed to cut 1/2" off of the top and sides of the antenna. So I took 1/2" off the top and 1/4" off each side.

    The result? Perfect 1.0 SWR! You can't beat that! Just glue the element down to the stubs and glue the lid back on and you're ready to fly
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  5. #5
    I Like Waffles... SENTRY's Avatar
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    I imagine you're pretty busy with antenna testing and tuning. Per frequency - what manufacturers/retailers would you suggest at getting great quality tuned antennas w/out having to modify them?

    900 / 2.4 / 1.3 / 5.8
    "I Like Waffles" : FPVLab on Facebook and FPVLab on Twitter

  6. #6
    Engineer for Jesus Christ IBCrazy's Avatar
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    Quote Originally Posted by SENTRY View Post
    I imagine you're pretty busy with antenna testing and tuning. Per frequency - what manufacturers/retailers would you suggest at getting great quality tuned antennas w/out having to modify them?

    900 / 2.4 / 1.3 / 5.8
    I would suggest buying from IBCrazy or readymadeRC, his partner in crime

    -Alex

  7. #7
    Navigator GoldCraft's Avatar
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    Thanks for sharing Alex.....

  8. #8
    I tested the resonance at 1160 MHz
    Alex, can you explain how you determine its resonant frequency? What equipment do you use?
    I finally got a SA a couple years ago but tracking generators and signal genorators that go to 2.4GHz+ are too expensive for me.

  9. #9
    Engineer for Jesus Christ IBCrazy's Avatar
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    I use a frequency generator and a directional coupler. Alternately you can use a regular SWR meter and a transmitter. Either method works fine.

  10. #10
    Navigator Rcmonster99's Avatar
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    Wow...what an eye opener....So I don't have a SWR meter or any whips and mirrors .... can theoretical values be checked against the patch ? for example, if I known what frequency I am using can I measure the element and then trim it to size ?
    Houba Houba !!!

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