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How is the telemetry transmitted to the RC?

Discussion in 'Pro/Adv Discussion' started by spankybear, Jul 5, 2015.

  1. spankybear

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    So on the pilot app there are 2 "s" meters (bars) on the screen. One is for the RC the other is for the video. Are they 2 separate signals? And if they are how is the flight telemetry getting to the RC? Is it on the lightbridge signal or he RC signal?
     
  2. Trumple

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    2 separate signals, 2 separate frequencies, hence 2 separate antennas. As for which one provides the telemetry...I *think* the "control" signal does, though I'm not certain. Only way to tell is to check out the telemetry when the video feed cuts out and see if it responds to any movement
     
  3. kyba274

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    I swear I remember reading here that both telemetery and video are sent on the same wireless frequency levels via the lightbridge.... Someone with more knowledge will have to chime in.
     
  4. danjordrone

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    Interesting
    Would be nice if we could all get to know all tech info how this lightbridge system does its thing
     
  5. Trumple

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    Well, let's break down what we know.

    We know there are two, independent signals sent between the RC and the P3, since one can drop out and the other can be fine, and the app gives two different readouts. As such, the two antenna must transmit on two different frequencies, otherwise they would simply strongly interfere with eachother to the point where the entire signal would simply be cancelled out by the other antenna. It also makes sense to split the video and control signals over two frequencies, since the video is such high bandwidth.

    IIRC the video is transmitted over 5.8GHz (because this is more susceptible to being reflected by buildings, ground, objects, etc.) and the control signal over 2.4GHz (again, less susceptible than 5.8GHz to reflection, which explains why your video signal drops out while your RC happily remains connected)
     
  6. FredzMaxxUAV

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    This is incorrect; everything is transmitted at 2.4 GHz. 2.4 goes much further than 5 GHz. Anyway, it's all 2.4 GHz on the P3.
     
  7. danjordrone

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    It states in dji spec its 2.4 system no mention of 5.8 at all
     
  8. Trumple

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    Yep you're right - for some reason I thought Lightbridge was 5.8GHz, sorry!

    The two signals must run on different 2.4GHz channels. Doesn't explain why the video feed cuts out more - must be a firmware thing (or simply an issue with unreliable streaming of the HD video...)
     
  9. FredzMaxxUAV

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    AFAIK they run one one channel only. When video is detected as being too low quality/far away, video just stops being sent, but control continues.

    From the Facebook group (Phantom 3 Owners): "Video feed and telemetry/rc are on the same link, just different packets. your rc tends to get further range because of how the allocate send/recieve packets over the air."
     
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  10. N017RW

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    The P3s LB system employs ODFM and MIMO technology.

    (Google it :) )
     
  11. Trumple

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    That's interesting. I wonder what the configuration of the two antenna is - MIMO perhaps? Also, why does the channel selection range from 13 to 20? 2.4GHz WiFi channels usually go up to channel 13, I'd be surprised if these operated on some extension of the standard 13 2.4Ghz channels...
     
  12. N017RW

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    Trumple likes this.
  13. BenDronePilot

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    The Phanton 3 does not use 5 ghz at all. And the inspire 1 remote uses 5ghz only for two pilot control operation where the 5.8 ghz is used to direct link the secondary control to the primary controller. The main control still uses 2.4ghz for both control and video.

    The P3 and Inspire 1 dual antennas work in a MIMO setup and are both in fact transmitting on the same channel at the same time. MIMO uses a technique called ODFM to differentiate the two separate streams coming out of each of the transmitting antennas to the receiving end. Explaining far beyond this begins getting much more complicated.
     
  14. N017RW

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    That's why I suggested to Google it.