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MX-20 range and antenna position

Discussion in 'Electronics' started by Scott Aubuchon, May 13, 2013.

  1. Scott Aubuchon

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    Let me pull this thread back up... so, I purchased / installed the above recommend mod to get the receiver up high. Strangely, I get even worse results. In the attached screen shot, flying at that height, I get a whopping 15% receiver strength. Antenna on the radio is straight up. If I'm on the ground and match the angle of the antennas (Tx/Rx) so they are parallel, I get 95-100% (within close range).

    Should I extent the plastic support to get the antennas to stick vertical? Could anything else be causing this?

    Also attached the GPX files, but what graph shows receiver strength?
     

    Attached Files:

  2. Gary Haynes

    Gary Haynes Administrator
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    Scott makes no sense at all. Something you could check is to make sure that the antenna cable inside the MX-20 is full inserted. Take the back off of the MX-20 (remember to remove both the battery and the MicroSD card first). You will see a small cable coming from the antenna and using a micro RF plug to plug into the TX. Check that it is fully inserted, perhaps unplug and replug.

    If that doesn't fix it the cable may have broken inside the antenna.

    Also have you tried another receiver to eliminate that as an issue.

    Do you have someone nearby with another MX-20 or receiver that you could swap out. It may be the receiver but there really isn't anything on it to check.

    Also if you have logging enabled in the MX-20 those log files will show great data on RX values.

    When i did my range testing earlier this year I didn't get down to 15% until I was out a 1.5 miles.
     
  3. Scott Aubuchon

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    K, well I'm glad I'm not crazy...o_O earlier this year I did drop the MX-20 on the antenna, but nothing appeared to break. BUT, thats not to say internally something didn't wrong. I will do what you suggested and take it apart to inspect. only other Rx I have access too it the GR-12 on the gimbal.

    Could it be the cabling from the Rx to the board?

    Thanks
     
  4. Gary Haynes

    Gary Haynes Administrator
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    Doubt that would affect the readout on the MX-20. And your GPX files show a solid RX signal from the RX. Very well could be an internal antenna failure.
     
  5. Scott Aubuchon

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    Thought Gary had saved me with a spare antenna he had sent... but I still don't like these numbers?



    Any other suggesting other than what Gary recommended? sending the transmitter in for check/repair
     
  6. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    Scott: The "jumps all over the place" would suggest that there is interference in the 2.4Ghz band which the MX-20 uses.
    Do you have lots of WiFi nodes around you, by chance?

    I realize your first posting was speaking about problems out on a golf course -- so my questions really only relate to the test you show in the video.

    Andy.
     
  7. Scott Aubuchon

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    This is what I see as I sit here... I am going to head out to a field and test again. I'm hoping its just some interference, but don't feel good about it.
     

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  8. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    Hmm. Just a couple of WiFi nodes at full strength. Would not have though that those would have caused problems, but....
    The next things I'd try are to approach a local RC model club and see if anyone's flying with an MX-20 and wouldn't mind letting you test your receiver briefly with their MX-20 -- and see if you get the same results (or ask nicely at a local hobby shop if they carry Graupner).

    Andy.
     
  9. Scott Aubuchon

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    Well... Not sure why I didn't think of this, but the problem is solved. It was the IB Crazy circular polarizer antenna that was causing the issue. Replaced it with the old whip antenna (per quadrocopter recommendation) and fixed.

    I could probably mess with the placement, but I think I'll just go with the whips for now. In one of the previous posts, you can see the placement in relationship with the receiver.

    I also tried different channels to no avail.

    So, we end another thread in closure... ;)
     
  10. Gary Haynes

    Gary Haynes Administrator
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    Scott which video tx are you using and what Freq? Also consider moving the TX out on a boom or landing leg to get it further away from the stack. If the TX is on 1.2mhz that might have been causing the issue. Or if it was high power version same might be true. Even with the whip I would suggest moving it.
     
  11. Scott Aubuchon

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    Not sure of the brand, but its 1.3ghz... the only channels on it are 8,9,H,C (whatever that means).
     
  12. Gary Haynes

    Gary Haynes Administrator
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    Yeah that freq combined with the BluBeam might do it. Try putting the TX elsewhere on the copter and it may go away. Distance does make the interference grow fonder....
     
  13. Josh Lambeth

    Josh Lambeth Well-Known Member

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    Did you have a low-pass filter on your 1.3? I need to get one on mine because im getting crappy reception as I go farther out with it...

    Josh
     
  14. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    Josh: The low pass filter may not help the reception quality -- it will pass the 1.3Ghz signal as before -- the original idea was that for 1.2 Ghz Tx, the first harmonic is 2.4Ghz -- right in the same band as the typical flight control Tx/Rx....so that's my understanding of why the low pass filters are used.

    Andy.
     

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