2.4 Ghz Channel Usage Detection

Discussion in 'Wireless & RF Design' started by jlatshaw, Oct 22, 2014.

  1. jlatshaw

    Thread Starter New Member

    Jul 20, 2013
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    Hello,

    So I have a quad copter (DJI Phantom 2) that I can fly using a 6 channel 2.4 GHz transmitter. From what I understand, each channel controls a certain component of the quad copter. I want to build an external circuit that will 'listen' for activity on a specific channel. What is the best way that I could detect if a particular channel is being used?

    Also, each one of the six channels is actually a specific frequency correct? If I could find out what the frequency of my channel of interest is, could I just build a simple bandpass filter to filter all but that frequency out and then from that detect if the channel is being used?

    Finally, I heard that these 2.4Ghz transmitters tend to preform frequency hopping, so does that mean that a given channel's frequency will constantly be changing?


    Thanks for any help,
    James
     
  2. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    Dont these remote controls use "spread-spectrum" as well as frequency hopping?
     
  3. Papabravo

    Expert

    Feb 24, 2006
    10,179
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    Simple and 2.4 GHz don't exactly go together. Have you ever built a circuit to work at 2.4 GHz? You might want to start your research by renting a Spectrum Analyzer. This will give you a picture of what is going on in the frequency domain. This probably won't be cheap, but it is probably better than having to buy one.
     
  4. MaxHeadRoom

    Expert

    Jul 18, 2013
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    If you just want to monitor one of the channels being used on the quad, buy another receiver for $10.00 and put a monitor circuit of some kind on the parallel channel .
    Max.
     
  5. alfacliff

    Well-Known Member

    Dec 13, 2013
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    arent those "chanels" just groups of bits in the digital stream from the transmitter?normal radio control has two definitiions, rf channel, and digital output channel. if you want to monitor rf at 2.4 ghz, get an Icom r3 reciever or something.
     
  6. MaxHeadRoom

    Expert

    Jul 18, 2013
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    If the channel you need to monitor is on the quad 'copter then a Y connection on that channel servo could be used.
    If it is land based or separate to the 'copter, then a parallel receiver could be used.
    What is the purpose for the 'listen for activity'?
    Max.
     
  7. jlatshaw

    Thread Starter New Member

    Jul 20, 2013
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    Thank you all so much for your quick replies.

    So my team and I are trying to build a system that we will mount externally on a quad copter. The user has a 'land' button, on the transmitter, that they will press when they want the quad copter to land. We want our system to activate after the user presses that button. So basically, we just want the system to activate when a certain channel has activity. Does that help explain the situation better?

    Also, we are university students, so we have access to labs, spectrum analyzers, etc.

    In response to the parallel receiver idea, are you saying that we could purchase the same type of receiver that is on the quad copter and isolate the channel of interest on the receiver to detect activity in that way? Also, will the transmitter sync to multiple receivers using the 2.4GHz systems?

    Thanks so much,
    James
     
  8. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Is this a normal RC transmitter or one of the quad copters that operates off of a Ipad?
    If the former, it is usually normal to buy other receivers for the same transmitter for other model use, there is a 'Bind' button on the TX to lock or bind any new RX to the same TX.
    If it is the Ipad type controller, I am not sure as they use the Ipad Wi-Fi signal.
    Do you have any numbers of the Transmitter?
    Max.
     
  9. jlatshaw

    Thread Starter New Member

    Jul 20, 2013
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    It is not the Ipad one. There is a physical transmitter: http://www.chiefaircraft.com/dji-dt7.html

    So I guess I'll look into buying an extra receiver and letting this be a parallel receiver which will listen for activity in the specified channel.

    Thanks so much for the help!
    James
     
  10. MaxHeadRoom

    Expert

    Jul 18, 2013
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    That is a little more high end than the one I have so the RX may cost a little more, the ones I use are cheap, but effective 6 ch.
    I assume the instructions would show how to Bind another RX.
    Ebay 171327232490.
    Max.
     
  11. jlatshaw

    Thread Starter New Member

    Jul 20, 2013
    28
    0
    Awesome. Thank you all very much for your help.

    James
     
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