MoCA Networking Has Me Stumped – Low Voltage on Cable TV/Internet Line?

Discussion in 'TiVo Help Center' started by mln01, Nov 13, 2019.

  1. mln01

    mln01 Member

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    Jan 10, 2006
    Charlotte
    I’m trying to help a friend set up a TiVo and two TiVo Minis using MoCA networking at her new house and I’m stumped. I’m familiar with MoCA, having used it in two houses, but something different is going on in this case.

    Before having my friend buy new splitters and Minis, I took my Holland MoCA-rated splitters and my two Minis to her house to test. She has a TiVo Premiere Elite, cable card and Spectrum-provided tuning adapter that are set up and working fine.

    I first disconnected the inbound Spectrum cable line to isolate the house system for MoCA and then attached my Holland 3-way splitter at the central A/V box inside the house to the coax lines running to the cable modem/Premiere location, and to the bedroom and the screened porch where she wants to use Minis. I also installed my Holland 2-way splitter at the cable modem/WiFi router/Premiere location.

    After changing the Premiere’s networking settings to MoCA+Ethernet, the MoCA network worked great. Both Minis were able to access and play shows recorded on the Premiere.

    But when I reattached the inbound Spectrum cable line everything fell apart. Not only did the MoCA network stop working (i.e. the Minis could no longer “see” the Premiere), but there was no internet access. This persisted after I shut down and restarted all the devices.

    I eventually gave up for the day and restored all connections to how they were before I started. Cable TV and internet were once again working fine.

    One surprising thing I noticed was an electric current on the inbound Spectrum cable line. When I reconnected it the final time I accidentally touched its copper core and felt the telltale tingle of electric current (much like I remember from touching a 9-volt to my moistened upper lip when I was a kid). I was surprised, and touched the copper again to confirm. Sure enough there was some low-voltage current in the coax. Perhaps I’m ignorant, or perhaps this offers a clue, but I’ve never before detected an electric current on a cable/internet line.

    It appears that the MoCA and internet signals were in conflict, although they are supposed to run on different frequencies, or perhaps the electric current on the line is causing the problem. I’m hoping something I’ve written here may resonate with someone on the forum and prompt an idea or ideas about what the problem may be and how to proceed. Thanks.
     
  2. schatham

    schatham Well-Known Member

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    428
    Mar 17, 2007
    Maybe you need a MoCA filter.

    Electric shock, that is not normal, you probably have a grounding issue somewhere in your house. Unplug the power to everything that is connected to the coax lines and one by one plug them in and see if you get shocked again.
     
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  3. kpeters59

    kpeters59 Well-Known Member

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    Jun 19, 2007
    Houston, Texas
    It's really common for there to be DC Voltage on the cable line. It's not supposed to be there, it just often is. It'll cause a hum on a Subwoofer fairly easily that can be a bear to track down. Maybe tell Spectrum to see if they can fix it. Possibly a MoCA Amp might isolate that?

    DOCSIS 3.1 modems can operate with higher frequencies that can interfere with MoCA function. If you're dealing with a DOCSIS 3.1 device, maybe try the higher MoCA channels, to see if that helps.

    I recommend that you bring your MoCA devices up one at a time so that the Nodes don't connect to other nodes that aren't helpful. A Mini has no need to connect to another Mini. Probably the Router, the TiVo and 1 Mini.

    Are you sure there's no MoCA active on the Router?

    -KP
     
  4. krkaufman

    krkaufman TDL shepherd

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    Nov 25, 2003
    Yeah, when you were a kid. You know you’re jonesing for another hit.
     
  5. krkaufman

    krkaufman TDL shepherd

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    Nov 25, 2003
    Yeah, Spectrum should ensure that the coax plant is grounded at the point of entry.
     
  6. krkaufman

    krkaufman TDL shepherd

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    Nov 25, 2003
    You most definitely need at least one MoCA filter, possibly up to three (yes, 3).

    You’ll need a “PoE” MoCA filter installed, and possibly a MoCA filter on the input of a Switched Digital Video (SDV) Tuning Adapter (TA) paired with the Premiere*, and a MoCA filter on the input port of your modem (as an alternative physical solution to the above suggestion to using a MoCA channel/frequency above the DOCSIS 3.1 frequency range).

    * A MoCA-enabled DVR and TA must be connected to your coax via a splitter, rather than the DVR being connected via the TA’s pass-through port, as the TA pass-through port severely attenuates signals at MoCA frequencies.​
     
    Last edited: Nov 17, 2019
  7. kpeters59

    kpeters59 Well-Known Member

    2,520
    507
    Jun 19, 2007
    Houston, Texas
    Yeah, except it's usually doesn't end up just being ground. Somewhere back up the 'road', some voltage got on the Center Conductor. Maybe a Distribution Amp or something. No amount of grounding at your location will eliminate it. It usually goes unnoticed until a Subwoofer is plugged in or some HiFi Audio Equipment that doesn't handle it well is connected. Or you unplug it and see a spark...

    I learned that lifting a ground on an Audio Amp can help eliminate the hum, but that's a different thread.

    -KP
     
  8. krkaufman

    krkaufman TDL shepherd

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    Nov 25, 2003
    What is the brand and model # of the modem you’re using? (To check if it’s DOCSIS 3.1.)
     

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