Moca budget loss question

Discussion in 'TiVo Help Center' started by plee82, Feb 17, 2020.

  1. plee82

    plee82 New Member

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    Is it just me or the Holland 8 way splitter works better without a POE filter? The insertion loss on the splitter at the MoCa freq is 17 db. The isolation max loss is 30 db. If I do not use a POE filter, the loss of two nodes in the output ports will be 30db. If I have a POE filter in the Input port, the loss between two nodes in the output ports will be around 34 db (insertion loss x 2). Is my assumption correct?
     
  2. tapokata

    tapokata Active Member

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    For a port to port signal path, the isolation loss along the signal path is added to the insertion loss in the path. From one output port to another, the signal path loss is -17dB + -17dB + -30dB. With a PoE filter installed on the input, the isolation loss is negated, although you suffer a modest -1 to -2 dB insertion loss from the PoE filter, or -17dB + -17dB + -2 dB.

    The isolation loss can be variable (why it is stated as a max value), up to the maximum. MoCA maintains data throughput rates up to -54dB path loss, but speeds drop quickly beyond that amount of loss.
     
    Last edited: Feb 17, 2020
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  3. plee82

    plee82 New Member

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    Thanks. What would the loss be from Output to Input port? Would that just be the insertion loss?
     
  4. tapokata

    tapokata Active Member

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    -17dB plus the PoE filter insertion loss along the path
     
  5. plee82

    plee82 New Member

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    Oh my question was in regards of no POE. If I had a node in one Output port and another one in the Input Port.
     
  6. tapokata

    tapokata Active Member

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    The loss would only be -17dB across the input to output.
     
  7. plee82

    plee82 New Member

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    That explains why the nodes talking to the node connected to the IN port have a TX power of -22 while the nodes in the OUT ports are at -3 TX power between each other. Currently using Holland 8 way splitter.
     
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  8. tapokata

    tapokata Active Member

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    An important thing to keep in mind is that MoCA, by design, is very robust and forgiving- a mid 50's dB insertion loss along a signal path takes some doing (most folks aren't using a passive 8 way splitter). While it's easy to obsess over getting the lowest power rates at each node, in reality the technology has been engineered to compensate for most typical CATV installations, where existing coax cable is damaged, connectors are not torqued properly, and various property owners have split and spliced at will. TL;DR version is don't sweat the -3dB Tx power- you've still got some headway in that signal path before it maxes out to have an effect on data throughput speed.
     
  9. plee82

    plee82 New Member

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    Yup. I get it. I was just thinking maybe I should replace the 8 way splitter with a 4 way starburst splitter I got since I only have 4 moca nodes. But at -22 and -3 I guess it doesnt matter.
     
    Last edited: Feb 18, 2020
  10. tapokata

    tapokata Active Member

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    You should be fine.

    But good practice / rule of thumb is to size the splitter outputs to the number of cable drops to minimize the insertion loss. Also invest in an inexpensive 20 inch-pound slip torque wrench for tightening coax connections (not coax to electronics- finger tight will do there- but coax to splitter inputs and outputs or other connectors not associated with a printed circuit board. And since your already mucking about, examine the cable condition to make sure they're all RG-6 and that the insulation is not comprised- any drop with more than 20' of excess cable should be cut out and joined with an F-81 barrel connector (-0.5 dB insertion loss for the connector, rather -2.5 db for the 20 foot of excess cable). And any open ports on a drop should be capped off with an attenuator cap...and...

    (yeah, it's a sickness).
     
  11. tapokata

    tapokata Active Member

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    Seriously, a POE filter on the input port should help the transmission power specs from all nodes...
     
  12. plee82

    plee82 New Member

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    I do wanna try that. Put my starburst 4 way splitter with a POE in the input.
     
  13. plee82

    plee82 New Member

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    Sorry to bring this up again but I went over a lot of Moca slides that explain budget loss and it seems like the port to port isolation between output ports is just what the spec sheet displays. So in the case of the Holland 8 way splitter, it is <=30 db.
     
  14. krkaufman

    krkaufman TDL shepherd

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    That is my understanding, as well. (e.g.)

    Even better...
    upload_2020-2-24_15-20-33.png
     
  15. plee82

    plee82 New Member

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    Does this really mean that for the 8 way splitter, not running the POE yields better results? Makes no sense in my mind though. I would think with a POE the port hop would still happen at <= -30db, plus it would get some reflected signal back from the POE that goes through the -17db x2 attenuation.
     
  16. plee82

    plee82 New Member

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    Got one of those amphenol hybrid splitter to use my 4 moca adapters. -16db port to port isolation is insane... my connections are ROCK solid now.
     

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