Design Issues and Solutions Is this cable suitable for DMX

Discussion in 'Lighting and Electrics' started by Crisp image, Sep 3, 2019.

  1. Crisp image

    Crisp image Well-Known Member

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    Following on from my last post "should I do this with DMX cable" I have been given some cable that is shielded twisted 2pr along the lines of Belden 8723 which has an impedance of 52 ohm and about 15 ohm resistance per meter https://catalog.belden.com/techdata/EN/8723_techdata.pdf
    Can this be used successfully for an install DMX run from box to stage?
    I am really interested in results here as I have quite a bit of it and a little project I could use it for.
    Regards
    Geoff
     
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  2. RonHebbard

    RonHebbard Well-Known Member Premium Member

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    Last edited: Sep 3, 2019
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  3. JD

    JD Well-Known Member

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    As Ron said, DMX is incredibly robust! However, compromised DMX has a habit of working just fine until 5 minutes into the show on opening night!
    I would heed Ron's caution list above. If it is not mission critical, then try it, but have a backup plan. 52 is a long way from 110
     
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  4. MNicolai

    MNicolai Well-Known Member Fight Leukemia

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    Comparing 8723 to 9451, it's not any worse than using standard mic cables. The characteristic impedance is one strike against it and the relatively high capacitance is another. Over long distances, the electrical properties of the cable will smear the clean edges of the digital signal and will cause "true"/"false" bits of data to turn into "maybe" or "the exact opposite true/false you intended". How long the cable is, what your environment is, and how forgiving the devices connected to it will all play into whether it's passable or not for you.

    Good practice for a reliable, mission-critical solution? No.
    Is there a fair chance it'll work? Yeah, if you're not taking it very far.
    Is it going to suck if during a ballet performance your rig goes into "Last 5 Minutes of Any Korn Concert" on you in front of an audience and then you have to pull new, better cable to prevent that from happening again? Also yeah.
     
  5. TimMc

    TimMc Well-Known Member

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  6. Crisp image

    Crisp image Well-Known Member

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    oops missed the 1000ft after the 15 ohm.
    But thanks for the replies. Think I will give it a miss.
     
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  7. eadler

    eadler Active Member

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    Cat5. From the official and testing side, there's this: https://tsp.esta.org/tsp/working_groups/CP/docs/DMXoverCat5_P3.pdf

    From the nominal side, Cat5 spec is 100 +- 15% (85 through 115; 100+-5 at 100MHz, 95 through 105).
    AES3 is 110 +- 15% (93.5 through 126.5)
    DMX512 portable cables per E1.27 shall be 100 through 120 ohms but 120 ohms is preferred as it is standard for RS485.
    High quality cable manufacturers keep their cable close to the spec's center. There's a chart of Belden Cat6 that shows a nice impedance line of random tests that show a low point around 97 ohms and a high point around 105 ohms. As you can see from above, anything that meets Cat5 (or 5e or 6) will meet AES3 spec. Cat5 will *likely* meet DMX512 spec (although it may drift out a bit)

    In short: Cat5e is cheap and readily available and will more than likely work just fine.
     
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