RG6 splitters & Comcast stupidity

Discussion in 'TiVo Help Center' started by Endymion_, Jan 22, 2020.

  1. Endymion_

    Endymion_ Member

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    Okay, I have a legitimate question that I have searched around quite a bit for but not found any definitive information on.

    MoCA frequencies. They go from 500MHz up to 1500. I could swear I remember seeing higher frequencies when I was reading all about MoCA maybe ten years ago, but that is the range that I see on Wikipedia currently.

    So, with a frequency range such as this, you might think that you would want equipment that is rated to pass frequencies such as this... at least to say it's tested for them, right? There are lots of splitters available that show this range on the product listing, and even list it on the front sticker, usually something like 5MHz - 2000MHz, or even higher. Well Comcast doesn't care. If you visit their forum, speak to their support, or to any tech that they send to your house, "those are garbage splitters that screw up your signal." I had a tech last week tell me that any splitter that is "gold plated," or that shows any rating higher than 950MHz - 1000MHz or so is a piece of crap that should be avoided.

    What I can't for the life of me get out of anyone is any technical reason why this is so, particularly when frequencies outside of the splitter ratings that Comcast installs are used by MoCA. I understand that Comcast, when training their people, might be trying to cut out any issues before they begin by simply saying "our splitters: good, everyone else's: bad," and that at least puts them to a standard. But their own X1 boxes use these frequencies. What exactly is it about these splitters, some of which even advertise MoCA compatibility, that Comcast hates so much?
     
  2. snerd

    snerd Well-Known Member

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    See this MoCA Best Practices document to more reliable information. MoCA frequencies extend to 1675MHz, and frequencies below 1000MHz were mainly used by DECA devices to avoid clashing with satellite receivers.

    Comcast just wants to blame your equipment for any problems that might occur so that they won't have to deal with it.

    The normal signal flow when MoCA devices communicate is this: A MoCA devices transmits signals up through the coax, and the signals go up through the "tree" of splitters until they reach the topmost splitter. The PoE filter on the input of the topmost splitter acts as a mirror to reflect the MoCA signals back down through splitters and coax to all the other MoCA devices in the house. The receiving MoCA device then figures out which signals it is supposed to receive, ignoring signals that are intended for other devices.

    Like everything else, there are good splitters and bad splitters. My personal opinion is the "MoCA rated" splitters are overhyped, kind of like "monster cables" for audio. As long as you have a MoCA PoE filter properly installed at the input of the topmost splitter in your "tree", any decent quality splitter with sufficient bandwidth will work fine. I have splitters from various sources, but have had no problems with splitters from monoprice.com, and they are well known for low prices on most of the stuff they sell.

    Having said that, if for some reason you can't use a MoCA PoE filter, then MoCA rated splitters such as the Holland M series should be used rather than ordinary splitters. The reason for this is kind of odd -- the "MoCA rated" splitters are intentionally designed to have poor isolation between the outputs of the splitter. This allows the MoCA signals to "port hop" directly between the output ports. In most RF systems, port hopping of signals would be considered a bad thing, and ordinary splitters are designed with as much port isolation as possible in order to avoid interference.
     
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  3. krkaufman

    krkaufman TDL shepherd

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    But the Holland GHS-PRO-M series splitters are also designed to have port isolation figures comparable to other cable-rated splitters in the sub-1 GHz range, right (i.e. the relaxed port isolation in these splitters is only within the MoCA frequency range, 1125-1675 MHz)?
     
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  4. krkaufman

    krkaufman TDL shepherd

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    Also, MoCA was designed to work with standard cable splitters (1 GHz), having the ability to adjust power levels, to a point, to overcome losses; further, a simple MoCA 1.1 network would only need a clean 50 MHz channel for operation, so a MoCA signal between 1125-1175 MHz wouldn't experience much more attenuation than a cable signal at 1 GHz (1000 MHz).

    As users migrate to bonded MoCA 2.0, or especially MoCA 2.5, where a wider frequency range is required for best performance, the splitter specs matter a bit more, especially if the coax plant is anything other than direct runs to a central splitter w/ PoE filter, as described by @snerd above.
     
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  5. Endymion_

    Endymion_ Member

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    Sep 9, 2011
    All right, this is better meat that I can chew on. Thanks for the link snerd, I'll digest it directly.

    I had these very splitters in use the last time they came out for a signal issue. It was nothing but badmouthing about the things with all kinds of colourful language. And the comcast forums are filled with all kinds of anecdotes that amount to little more than "don't use them," nobody ever elaborates. I guess when you are trying to train someone who might not have a high school education (their techs) it is simpler and easier to just keep it with the company equipment.
     
  6. snerd

    snerd Well-Known Member

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    I believe that is correct, in the sub-GHz range they should behave the same as ordinary splitters.
     
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  7. snerd

    snerd Well-Known Member

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    Sort of. MoCA actually divides a 50MHz channel into a bunch of independent sub-channels, and measures the characteristics of each sub-channel in order to optimize overall data flow through the 50MHz channel. Technically, that doesn't alter the amount of attenuation, it just tries to compensate for varying amounts of attenuation across the (unclean) 50MHz channel. A lot of modern RF systems (e.g. DOCSIS 3.0, 3.1) play similar games. The difference with MoCA is that the specific path for each pair of MoCA devices is constantly measured and tweaked to optimize data flow for whichever pair has use of the network.

    The problem with old splitters is that they were never designed or charachterized at the higher frequencies. Some might work fine, others not so much. Using splitters that are spec'd to handle higher frequencies is likely to allow better MoCA communications.

    The specs matter more in the sense that the splitters need more bandwidth overall. The same games are still in play to compensate for any "uncleanliness" in whichever broadband channels are employed. If your argument is that using "MoCA rated" splitters becomes more important for MoCA 2.0 or MoCA 2.5, I don't believe that is necessarily true whenever a PoE filter is used.
     
  8. krkaufman

    krkaufman TDL shepherd

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    OK, but the very basic points were (1) that attenuation increases with frequency, but (2) the typical MoCA 1.1 network operating at 1150 MHz won’t experience much different attenuation from a cable signal at the top end of 1 GHz (so a splitter rated for cable, 1 GHz, would likely work as well as a “designed for MoCA” splitter).

    Eh, I’d think using splitters actually rated and tested for the full MocA 2.0 spectrum would be more relevant as the MoCA devices require greater portions of that space — whether port jumping or not.
     
    Last edited: Jan 22, 2020
  9. snerd

    snerd Well-Known Member

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    That's why I wrote "... the splitters need more bandwidth...", meaning rated to 1675MHz or above.
     
  10. krkaufman

    krkaufman TDL shepherd

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    Sure, but that wasn't all you said, which is why my reply was phrased the way that *it* was.

    Both this tangent and I are past our bedtimes. I concede all points on the matter, explicit or implied.
     
  11. Sparky1234

    Sparky1234 Well-Known Member

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    Wow, best practical MocA discussion on splitters I have seen. Thanks krkaufman and and snerd.
     
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  12. Fugacity

    Fugacity Member

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    Brighthouse would split the line with a comscope 2way one to the cable modem, and then put a poe filter on a holland splitter for the whole home dvr setup. So far Spectrum has my line juiced so high that the POE filter in front of all the things on a 3way filter doesn't effect the 400mb modem connection.

    But the post brings up an interesting thought in their setup in that by doing that they severely limited the possibility of crosstalk with the cable modem at all by essentially creating a firewall to keep cable modem away from any of the set top boxes/DVR communication.
     
  13. krkaufman

    krkaufman TDL shepherd

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    Wouldn’t the PoE filter be irrelevant to the modem connection if the modem is hung off a separate output of the Commscope 2-way splitter?

    Providers tend to prefer getting maximum signal strength to the modem, employing a 2-way as you’ve described. Keeping the modem path isolated from MoCA signals is useful if the coax and equipment (spec, locations) allows, especially with the advent of DOCSIS 3.1, which overlaps with MoCA frequencies.
     
  14. Fugacity

    Fugacity Member

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    Yes, but I wrote that in a confusing way. Spectrum doesn't use moca stuff for their non legacy customers and they only put in a single 3 way splitter in my wiring cabinet when i switched from directv in november. I'm in the middle of finishing the basement remodel and misplaced the brighthouse splitters and filter so I bought new stuff on amazon and its slowly making its way through the mail. The Tivo POE filter got here first so I tested to see if it would cause issues with the modem and if i could skip the double splitting. Will have to see later if the moca communications mess with it.
     
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