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Thread: Fatshark attitude interference with 72mhz

  1. #1
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    Fatshark attitude interference with 72mhz

    I'm having real bad interference issues with the 72mhz rc control on my plane. I am using a corona receiver and the 250mw video tx that came with my new attitude goggles. Here is a short video showing my set up. When the video tx is powered up it literally cuts my range check distance by greater than half, closer to 2/3rd of what it should be.



    I posted this in RC groups too but got no help. I flew two flights with no issues, on the third flight I lost control of the plane at 300 yards. Here is a video of the crash.



    Please help guys, I am lost right now. Thank you.

  2. #2
    Wireless video evangelist FatShark's Avatar
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    Well, the 250mW TX is designed to be friendly with common RC frequencies and the switching frequency of the regulator selected so its not harmonic on any common RC frequency. That said I do see some problems with your setup:
    1) Your camera, TX, power cabling is very long and not filtered, any noise will radiate nicely off those wires. At the very least some filtering at cable endpoints would be a good idea.
    2) I can't say for certain what model camera you are using, but it looks like those new 600+TVL OSD cameras that have a 5-15V input. I've tested some of these "FPV cameras" from some vendors and they aren't particularly friendly on RC frequencies especially at the lower frequency range. I'd get that camera away from your RX stuff, shorted up the cable and put some filtering in there. I can't say for certain that is the case with your camera as you've purchased it from a reputable retailer.
    3) You should expect a decrease in range to about 2/3 normal anytime you put transmitting equipment in the same vicinity of your RX. I haven't flown 72Mhz for a few years but when I did I did 2 things: 1) tuned the RX antenna length and 2) ran the RX antenna straight out the bottom of my plane and let it dangle down.
    FatShark - RC vision systems - www.fatshark.com

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    Thank you

    OK, thank you for the help. I messed around with the system yesterday for a few hours and found a few things.

    -I twisted all the servo leads
    -I powered the receiver with a separate batt with the same results.
    -I powered the video tx with a separate batt with the same results.
    -I tried testing the rc rx ant polarization with different positions (up, down, down the wing) and it helped a little, but not much.
    -I installed another corona rx with the same results.
    -I installed chokes on the power wires going to the video tx near the tx and it didn't help much.
    -I installed a choke on the neg lead from the video camera with no real results. This is the camera I am using.

    http://www.readymaderc.com/store/ind...roducts_id=582

    Today I will try and disconnect the camera and see what that does to the range.
    I will also try different servos and get rid of the hxt900 I am using.
    I will poke around the forums and figure out how to tune the rc rx ant length.
    I will try different channels on the video tx.

    Questions:

    You say i should shorten up my video tx and camera cables. Does this mean I can't power the system through my flight pack anymore? I'd really like to use the LC filter that came with the video tx so I don't have to use a separate batt to power the video system. That being said, it is a solid 3 feet between my camera and rc rx/ant, not sure I can get it further away than this.

    Thank you for the help, I'll get to work now.

  4. #4
    Wireless video evangelist FatShark's Avatar
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    How did you record the 2nd video? It looks like it was recorded with an onboard recorder (no static, rolling shutter).
    FatShark - RC vision systems - www.fatshark.com

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    5.8 issues

    Yes, the onboard video was with a separate video camera from hobby king, it survived, but just barely.

    I spent the day trouble shooting again. I made another video of my progress. Still have no idea what could be causing this, I've tried everything I can think of and still have terrible interference. Here is an update video:


  6. #6
    Wireless video evangelist FatShark's Avatar
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    Ok wow, big missing piece of information just came out. Your HD camera is the 1st place to look. HD cameras are notoriously RF noisy.
    Do a quick google search on "Hobby King HD camera RF noise"

    You need to simplify your setup and progress one step at a time. Don't use an HD, use a battery to power your camera/TX separately for the 1st flights or so to get a bearing on your range, then try sharing the pack. the problem with long cables is they act as radiating antenna for any RF the FPV components may generate.
    FatShark - RC vision systems - www.fatshark.com

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    5.8 issues

    This is the cam I had on the plane during the crash.

    http://www.hobbyking.com/hobbyking/s..._5MP_CMOS.html

    However, I have not used that camera during these range checks and still have unsatisfactory range.

    I read in another thread someplace that the main leads from the batt to the esc should be kept short. If you need to extend leads you should extend on the esc to motor side and then twist/braid them. Is it possible this may be the problem? I did notice when I powered the rc rx with a separate nicad batt and left the main power leads unplugged I had significantly more range. When I plugged the main flight batt in though the problem came back. This was all with the video tx powered up.

    Also, I tried not using the long braided cable from the flight pack to the LC filter and instead powered the video tx right at the LC filter with a separate flight pack. So, the only cable was the short 1" power cable from the LC filter to the video tx, and the 2" cable from the camera to the video tx. Again, same issues.

    I'm going to buy some more chokes and install some on the servo wires. I'll also shorten the main power cables from the batt to the esc if you think that's a good idea.

    Thank you for your help, this is turning into a headache, sorry.

  8. #8
    Wireless video evangelist FatShark's Avatar
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    It's a love/hate thing. On one hand you want FPV to be simple but at the same time part of the fun is in the challenge of optimizing the performance. There's a lot going on with conflicting gear on an FPV plane. Trying to put a bi-directional link on different frequencies sharing the same small area is technically very challenging.
    The only way to be successful is to keep everything minimal and make incremental changes. Its a shame such a nice plane was ruined but a cheap RTF foamy is ideal way to prove out your systems before risking nice planes and gear.
    Keep posting here and we can all learn from your experience towards success. Hopefully some others can chime in here that are using similar gear.
    FatShark - RC vision systems - www.fatshark.com

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    5.8

    Can you recommend a camera I can record with that won't cause the RF interference problems the hobby king camera causes? I'd prefer not to use a go pro as they re too expensive and big/heavy.

  10. #10
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    Fixed

    Got the issue fixed. I've attached a somewhat long video, but long story short I replaced the corona rx with the futaba pcm rx and added chokes to the servo wires. I also shortened the main power leads and extended the leads from the esc to the motor then braided them. Works great now, time for a test flight.




    Sorry for the long vid.

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