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Thread: An idea of how to decrease RF interference when using 2.4 ghz for video

  1. #11
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    Quote Originally Posted by Daemon View Post
    It's sometimes done the other way around, just to have a smaller lighter antenna in the air.
    Yes, you can use linear polarized antennas on your craft, but get ready to experience huge losses when banking or maneuvering. There is only one method to avoid this: use a CP antenna on one of the ends, either TX or RX.

  2. #12
    Quote Originally Posted by cold_dog View Post
    Yes, you can use linear polarized antennas on your craft, but get ready to experience huge losses when banking or maneuvering. There is only one method to avoid this: use a CP antenna on one of the ends, either TX or RX.
    And you lose half your power by mixing CP and LP. My point was nobody I know flies with CP on the aircraft
    and LP on the ground. Everyone who uses CP on the aircraft uses CP on the ground.
    The only time I see em mixed is with LP on the aircraft for lower size/weight/drag (small aircraft)
    with CP on the ground.

  3. #13
    Pilot Dionysos's Avatar
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    just use a different channel!

    Scherrer has done a test with horizontal polarization on the plane. Doesn't work. No need to repeat what's already been done.
    Latest Crafts: The Anti-Gravity-Machine, Carbonator, Guava 2m, Wunderwaffe I, Wunderwaffe II, Uberwaffe, Plankton v2, TBS discovery

  4. #14
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    Quote Originally Posted by Daemon View Post
    And you lose half your power by mixing CP and LP.
    When you mix CP and LP the loss is 3 db. That's not a half, to be precise

    just use a different channel!
    I use 2370 mhz. The idea was to get further gain in signal to noise ratio when flying in areas pulluted by interference on 2.4 ghz.

    Scherrer has done a test with horizontal polarization on the plane.
    But he did that for 433 mhz RC or for 2.4 ghz video?

  5. #15
    Quote Originally Posted by cold_dog View Post
    When you mix CP and LP the loss is 3 db. That's not a half, to be precise
    I said half power, not half range, and yes -3dB is half.. almost precisely. +3dB = 1.995x

    How about this. Get your hands on a spectrum analyzer with a linear antenna, and measure
    the noise floor near your chosen frequency with antenna held vertically and again with it held horizontally.
    Report back. I'll bet you see very little difference. Certainly not the >10dB difference you think.
    Last edited by Daemon; 30th September 2013 at 02:25 PM.

  6. #16
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    Bumping for more info. Horizontally polarized antennas never became the norm for 2.4 video...are there good references to testing or experiences out there that arent showing up with a search? I've got a 433 dipole that I was thinking of cutting down to 2.4ghz and running horizontally polarized this weekend on the wing paired with a horizontal yagi on the RX.

  7. #17
    Instructor Pilot Channel 1's Avatar
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    Quote Originally Posted by Tronski View Post
    I've got a 433 dipole that I was thinking of cutting down to 2.4ghz and running horizontally polarized this weekend on the wing paired with a horizontal yagi on the RX.
    I would be interested in knowing how it works out, BTW don't forget to skew your yagi when banking.

    Wayne
    Everybody loves a bunny.

  8. #18
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    will do for sure. I cant do much of a scientific test, but I've got a peak that I flew to last winter that I can no longer get to. Its not far at all (~2 miles), but my town is between me and the mountain peak. CP/helical and vertically polarized antennas cant get me there anymore for some reason even though my set up is still working fine for out in the boonies.

    I tested CP on the wing with horizontal yagi on the RX and it did seem to work well in a known good area. I want to take that one step further and put a horizontally polarized antenna on the wing so that I don't loose so much signal. I figure a horizontal 1/4 wave dipole on the wing will still give me more power at ~2 miles (even at the antenna nulls) then a low gain CP antenna feeding a horizontally polarized yagi. Lack of other people doing this makes me pretty sure it doesn't work out though lol.

  9. #19
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    I only had one free flight today for testing and I left my phone on in my pocket haha. The other flights I was getting stepped on by my friend so it will be a few weeks before I can give it a real test

  10. #20
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    and coming back to this. I've abandoned the horizontally polorized antenna. It just didnt seem to make and improvment and was worse overall I'd say. This may have been from my build job or the nulls pointing at me more often. Either way I'm back to vertical.

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