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shielded cable helpful here?

Discussion in 'General Electronics Discussion' started by drmax, Dec 30, 2013.

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  1. drmax

    drmax

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    Dec 30, 2013
    Hello. I'm wondering if I should replace this standard 2 wire cable, with a shielded hdmi cable, if it will reduce the "common mode noise" induced by the electromagnetic interference which I am receiving? (usb power switching) Or, should I just buy some of those ferrite clips and put on either end and call it a day. I am using this device in a gen aviation aircraft to extend out a couple items, and thought that a shielded cable may help. Let me know before I proceed in creating another issue with the shielded cable. Also, if you recommend the new cable, how would I then introduce the shield to this circuit? Here is a picture of the device as sold on line, that I am referring to. http://dx.com/p/3-socket-triple-soc...57256?tc=USD&gclid=CJLK39-Y2LsCFbA7MgodWWAA2w
    Thx, DM
     
  2. Arouse1973

    Arouse1973 Adam

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    Dec 18, 2013
    Hello
    I don't quite understand what your trying to do, can you explain a bit more. What is the cable doing, why HDMI?. Just bog standard twisted pair cable is quite good at reducing CM noise, that is if it is CM noise. Is the cable transferring data or power.
    Thanks
    Adam
     
  3. drmax

    drmax

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    Dec 30, 2013
    Hello. I didn't get an alert I had a reply even though I thought I had this set up for instant notification...The cable in question, is supplying 12V dc to a small gps battery for continual charging. I was told this is a magnetic interference. The noise is brought into my aviation headset. When I unplug it, the noise goes away. I am not alone with this noise. I understand it's been around for years. I thought that possible a shielded cable would help, hence the hdmi cable as it as that outer shield. I don't really know much about what I'm doing, so needed to ask. If the existing (normal cig lighter plug cable with the standard wire that comes with it) is sufficient, I was leaning on snapping a pair of the ferrite chokes on either end, to help reduce noise.
     
  4. mursal

    mursal

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    Dec 13, 2013
    Does the noise go away if you turn the engine off?
     
  5. drmax

    drmax

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    Dec 30, 2013
    No sir. Only when I unplug that one charging cable, to the external portable gps battery.
    Any idea why I am not getting email notifications? It's turned on
     
  6. shrtrnd

    shrtrnd

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    Jan 15, 2010
    Since we don't know the problem, you have to experiment.
    Arouse1973's twisted pair (I'd use shielded, twisted pair) can't hurt.
    I'd be extra-careful watching where you ground the shielding, as the grounding shield
    is your best bet in beating this.
    You may not be able to eliminate this problem with this method, but you should be
    able to reduce it, if nothing else. Good Luck.
     
  7. Arouse1973

    Arouse1973 Adam

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    Dec 18, 2013
    Shielded cable will only help if the noise is air bourne. If its in the cable it will only stop the cable radiating not solving the problem. Shielded cable is only really effective with a 360 degrees seal. The old fashioned pig tail is rubbish at this an is only any good at at a few Mhz.
    Thanks Adam
     
  8. Arouse1973

    Arouse1973 Adam

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    Dec 18, 2013
    You were told what was magnetic interference? If you unplug your headset then it will go away, you won't hear anything. What do you mean the noise has been around for years.
    Thanks Adam
     
  9. drmax

    drmax

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    Dec 30, 2013
    When I unplug the charging cable, the noise goes away. This has been a known problem for years and it can be hard to "reduce" (not just me) I may possible just route that charging cable differently. Here is a picture of that battery. Just imagine the charging cable as being an additional cig adapter, wire and plug. http://ifly.adventurepilot.com/portals/0/documentation/iFlyBatteryManual.pdf
     
    Last edited: Dec 30, 2013
  10. davenn

    davenn Moderator

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    Sep 5, 2009
    Hi drmax
    welcome to the forums :)

    it sounds like the GPS unit charger is possibly a switching regulator and is outputting noise onto the DC rail. small ferrite beads and also filter caps may solve the problem

    it IS going to require some experimentation


    Dave
     
  11. drmax

    drmax

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    Dec 30, 2013
    So the ferrite clips I can get from Radio Shack is the place to start, right? Also there then is no reason to add a shield cable in place of the other? I mean it will not help in noise reductions? Thx again and like a dummy I didn't ck my spam folder. The replies were there....:p
     
    Last edited: Dec 31, 2013
  12. Arouse1973

    Arouse1973 Adam

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    Dec 18, 2013
    I agree with Dave, ferrite beads in the wires. But make sure they have the correct current rating, otherwise they will be useless. Try a small capacitor after the ferrite connected to 0volts this will form a low pass filter and which will attenuate high frequencies better than just a ferrite on its own. If is common mode noise you might need a cm choke for the power rails. Twist the wires together anyway.
    Thanks Adam
     
  13. davenn

    davenn Moderator

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    Sep 5, 2009
    no, not the big clip on clamps the really small beads that the individual wire will fit through

    [​IMG]

    a few mm long, a few mm diameter
    the capacitors will be disc ceramics in the range of 0.1uf to 0.01uF range

    cheers
    Dave
     

    Attached Files:

  14. Rleo6965

    Rleo6965

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    Jan 22, 2012
    I agree with Dave. Some Switching Power Supply have 22khz. Possible that frequency have varied to near audible frequency range due to charging load current. Do you still hear noise when the Battery Pack was almost fully charge?

    Does Battery Pack have a Metal Ground Screw connection to be connected wire to vehicle metal ground?

    Or try reduce the wire length and change to bigger wire of charging cable to avoid voltage drop.
     
    Last edited: Dec 31, 2013
  15. shrtrnd

    shrtrnd

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    Jan 15, 2010
    I don't know if this helps, but most aviation electronics I've worked on operates at 400hz. Is it possible this add-on electronics is not designed to filter-out the possible
    400hz of the airplane's electrical system?
     
  16. Arouse1973

    Arouse1973 Adam

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    Dec 18, 2013
    If it is 400Hz then a ferrite bead won't do the job, they are for higher frequencies. Are you able to measure the noise on a scope and tell us what frequency it is.
    Thanks Adam
     
  17. drmax

    drmax

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    Dec 30, 2013
    Since I do not know what I'm doing, can you give me the layout of the size of ferrite clamps to clamp onto the ends of the wire, as well as the size of the caps? Thank you
     
  18. davenn

    davenn Moderator

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    Sep 5, 2009
    reread the other posts, obviously you havent ;)



    Dave
     
  19. drmax

    drmax

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    Dec 30, 2013
    I'll need to find a different forum to find out "how to" for my intermediate electronic knowledge, I suppose. I've seen the advice and I do thank you. I see the round chokes, and I suppose I run the cable through and either coil the wire around it, or zip tie it. That is one thing I don't understand.
    Getting a cap inline I'll just hold off on that and try the other first. I need to have better understanding of how this all works, before I create more problems. Thx
     
  20. drmax

    drmax

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    Dec 30, 2013
    Dave, do I just use one of those on either end and then run some electrician tape around it to keep it in place? Are the clamp on ferrite filters the same thing? Those I would not have to cut an end off to get the wire through, is my reasoning of using that style. My local radio shack has a very small clamp style that would grip the wire. Thx DM
     
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