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Thread: cable modem signal levels

  1. #1
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    cable modem signal levels

    this is what i go by just incase anyone is using the 192 diag to pull up info. if you are ourside of this than that is probably the cause of your porblems.
    signal to noise = 30-35
    downstream power level (or just power level) = +5-
    upstream power level = 40-50
    signal to noise, or carrier to noise, is a ration expressing the amout of signal at a given point compared to unwanted "interfernece" if you will
    downstream power level is the amount of signal that is reaching a given point. the sgnal come from the cable co's head end.
    upstream power is the amount of signal comming out fo your modem heading to the head end. it is important that this signal is not too low so that it can stay out of the "noise floor" and reach the head end at an acceptable level. also if it is to high it will overwork your modem and cause sporatic drop offs in service.

    think of it like this 40-50db is like me and you talking at a close distance in a normal tone....30 would be me wispering and you struggling to hear me over erverthing else around us. 55 and i am screaming. eventually my voice will want a break and i will stop yelling until it feels better.

  2. #2
    Second Most EVIL YARDofSTUF's Avatar
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    I always wondered about what was good or not, and hwo to tell. thanks for the post.

  3. #3
    Regular Member buckifan's Avatar
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    Quote Originally Posted by travis2144
    upstream power is the amount of signal comming out fo your modem heading to the head end. it is important that this signal is not too low so that it can stay out of the "noise floor" and reach the head end at an acceptable level. also if it is to high it will overwork your modem and cause sporatic drop offs in service.
    There is nothing that the end user can do to change the upstream level at the CMTS. The output level of the CM is adjusted automatically until the level at the CMTS is acceptable (usually 0 dbmv). If you add more loss by adding a splitter the CM will automatically raise its output by the amount of loss added. The end result is that the level at the CMTS remains unchanged.

    Acceptable upstream output from a CM is between 35 to 50 dbmv.

  4. #4
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    yes that is right, are you trying to say that i am not b/c i was strickly talking about the return coming out of the modem...also 35 is low, i see modems that low drop off all the time, esp in poorer systems with high common path. ok i get what you are saying now...once you hit the first actives return amp it taked over but you still have to have your modem in that sweet spot to get to that active solid. i guess heading to the headend could be better stated by heading through the actives and the rest of the plant to the headend.
    Last edited by travis2144; 09-12-06 at 07:31 PM.

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