Question about diplexer & interference with MoCA adapters

Discussion in 'TiVo Coffee House - TiVo Discussion' started by cambot, Mar 4, 2018.

  1. cambot

    cambot New Member

    Nov 21, 2017


    Got a technical question for you guys. I've bought a few of the Yitong bonded MoCA 2.0 adapters and they've been rock solid so far for 1 Gbps speeds, so I got more to set my parents up with OTA TV and Ethernet for smart TV sets (they've got some loathsome Cat2 cabling so MoCA was the only way to go). At their wiring closet, I'm using a BAMF 5-2300 MHz 4-way splitter. Some of the rooms with TV sets have the gigabit MoCA adapters to de-diplex the Ethernet and OTA signals, and others don't.

    My question is about the rooms with cable runs that connect directly between the MoCA splitter and a TV set. I haven't noticed any interference from the higher MoCA freqs while watching OTA channels on these TVs. But 'should' there be interference from MoCA whenever there's Ethernet signaling, due either to different wattages between the MoCA and OTA inputs in lieu of port isolation or to passive intermodulation? I'm just curious whether those rooms really need diplexing if only OTA signals are being used on a given outlet. Thanks!
  2. mdavej

    mdavej Well-Known Member

    Aug 13, 2015
    I don't think they need them. There is no impedance or voltage matching or intermodulation at play. It's simply filtering the frequencies on each port, essentially blocking Moca frequencies on the TV port. I don't think antenna inputs on a TV will even see Moca frequencies because they are well above channel 69, the highest OTA channel.

    I use diplexers with OTA essentially as POE filters. I use a single pair of diplexers in my entire 5 TV system - one to inject Moca at the bridge near my router and the other to inject OTA at my antenna. A simple splitter would probably work just as well at my Moca injection point, but I think the loss is lower on a diplexer.

    Try removing one. Shouldn't hurt a thing. If you have one near your antenna and don't have a POE filter, leave that one.

    And yes, I realize that a diplexer does not filter Moca quite as well as a POE, but in practical terms, there isn't enough Moca left to do any harm whatsoever.
    Last edited: Mar 4, 2018
  3. lisabranam

    lisabranam New Member

    Apr 5, 2018
    I think antenna frequencies are different from the Moca frequencies. The best way is to hire some technical guy who understands the frequencies so you do not end up wasting money without getting it done correctly.
  4. snerd

    snerd Well-Known Member

    Jun 6, 2008
    Althogh some devices can have interference from MoCA signals (e.g. tuning adapters and some modems), if you aren't seeing problems on your TVs then don't worry about it. MoCA devices exchange data continuously whether or not ethernet traffic is flowing between them, because MoCA is always testing a slew of sub-channel frequencies to determine the best scheme for exchanging data between each pair of MoCA devices, and adapts to changing conditions on the coax. That is why the PHY rate for MoCA is significantly higher that the usable data rate.

    So, if you have MoCA devices powered up on the coax and you're not seeing interference, it is very unlikely that you'll see interference when actual network traffic is part of the MoCA signal.
    fcfc2 likes this.
  5. V7Goose

    V7Goose OTA ONLY and Loving It!

    May 28, 2005
    New Mexico...


    I know nothing at all about the specific devices listed in the OP, and I see no reason at all to use a diplexer in a simple OTA setup.

    But I wanted to simply note that I have a MoCA setup on my OTA cable plant, and the same coax that goes to my MoCA devices also goes straight to my three different TVs and two receivers for radio reception through simple splitters, and I have absolutely no problems at all.

    Note that any MoCA setup is simply an extension of your existing Ethernet LAN that allows the same Ethernet communications that are normally restricted to twisted pair or wireless to also travel over coax to any device that can use them. Those signals are ignored by any device that does not operate in the same frequency band, just like UHF TV signals do not cause any interference with a VHF device. In a similar way, powerline Ethernet adapters simply extend those same Ethernet signals to the electrical wiring in the building.
    Last edited: Apr 10, 2018
    kpeters59 likes this.

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