RGB and 2*XLR down one Cat5?

Discussion in 'The Projects Forum' started by jss10, Jul 13, 2015.

Will it work?

  1. Yes

    0 vote(s)
  2. No

    0 vote(s)
  3. Yes, but with adjustments

  1. jss10

    Thread Starter New Member

    Jul 13, 2015
    I work in the broadcasting industry and am constantly looking for better ways of doing things. Right now we have 3 500 FT reels to roll out for the broadcasts to carry the video signals from the cameras and the intercom for the headsets to our production trailer. This works well and all but 10 ft of this cable weights about 30 lbs and it would be much easier just to use Cat5.

    In this project of mine I'm going to try and fit RGB (Component) video and 2 XLR signals down one Cat5 cable using a breakout box on each end. Is it possible to passively send this down one cable without melting the cable or corrupting the video signal?

    Here's how I see it: A cat5 cable has 4 twisted pairs for a total of 8 wires. I would use 3 of the wires for the component signal, 2 for one XLR, 2 for the other XLR, and use the last wire as a ground. Will this work? Can I have all of these cables use the same ground or will it cause too much interference?

    Please point out anything that could go wrong or won't work.
  2. Papabravo


    Feb 24, 2006
    There is a reason why the pairs of wires are twisted and your use of them defeats that purpose. 500 ft. of Cat5 will greatly attenuate the video signal to the point where there might be nothing left. Sounds like a really inferior plan. That said, if you want to run the experiment -- who am I to dissuade you.

    The XLR (audio) signals may be OK since they are differential and don't require a separate ground, but the standard 3-pin connector uses the third pin for a cable(chassis) ground. This would not be available in your Cat5 scheme. Also XLR connectors are designed to carry power to loaudspeakers, up to 15 Amps if I recall correctly. This might be a problem for for the 24-26 AWG wire in Cat5 cable.
    Last edited: Jul 13, 2015
  3. AnalogKid

    Distinguished Member

    Aug 1, 2013
    First, the easy part - you will not melt the cable if the audio signals are line level and not speaker drivers.

    Second, this will not work. 500' audio runs need *shielded* twisted pairs, with no signal current in the shield. Combining the grounds of the three video signals will not work because the resistance of 500' of *anything* will be enough to develop common-mode noise among the signals, not even counting the audio ground current noise. This would not work even if you had five ground wires, one for each signal, because standard video is designed for 75 ohm coax that is properly terminated on both ends. You could design and build an unbalanced-to-balanced driver and receiver and use transformers to create balanced pairs for each video signal, but that would take 6 wires. I pretty much guarantee failure with a single ground wire and no shielding if you are hoping for "broadcast quality" results.

    Count your blessings. Before Philips invented Triax, TV-81 cable weighed about 1/2 pound *per foot*. Try hauling a mile of that around a golf course.

    Papabravo likes this.
  4. DickCappels


    Aug 21, 2008
  5. Nykolas


    Aug 27, 2013
  6. crutschow


    Mar 14, 2008
    There are some Component to CAT5 extenders listed here that say they will go to 1000 feet, which may work for you.
    But you would need a separate cable for the audio.
  7. jss10

    Thread Starter New Member

    Jul 13, 2015
    Currently we're using ~20awg wires to transport the composite signal over the 500 ft and the same gauge for the XLR signal granted there is a ton of shielding. We do have an amplifier in the production trailer that boosts the signal and I figure with using 26awg cable there would only be less resistance. If the problem is shielding could I use Cat7 cable?

    Also related: We have a 250ft Cat5e cable that we use to transfer non-essential video to and from the pressbox such as the scoreboard cam and program monitor. We have 2 BNC balun's with what looks like some transformers on the inside. Here is the exact model: http://www.bhphotovideo.com/c/product/852273-REG/MuxLab_500037_Quad_Video_Balun_with.html

    I would like everything on the end of the camera to be passive but I'm okay with having something powered on the receiving end.
  8. djsfantasi

    AAC Fanatic!

    Apr 11, 2010
    26awg wire has more resistance than 20awg. 26awg is about 40.8Ω per foot; 20awg wire is about 10.1Ω per foot.
  9. jss10

    Thread Starter New Member

    Jul 13, 2015
    Yeah I totally got that wrong. Both the cables are about the same gauge.
  10. ebeowulf17

    Active Member

    Aug 12, 2014
    Your point is still correct, but aren't those resistance values per 1000ft, not per foot?
  11. djsfantasi

    AAC Fanatic!

    Apr 11, 2010
    Slip of the decimal point. I need new glasses. This pesky black things move on their own
    ebeowulf17 likes this.