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Re: Recommended modem levels?

Due to the very specific problem you are having, my first guess is that you may have a CMTS configuration problem. Though there may be RF level issues that are causing the MTAs to drop.

The recommended -15 to +15 dBmV DS level is correct and if the DS levels fall within this window, the modems should work just fine, assuming no DS impairments causing MER/BER degredation.

Very generally, if a system is designed and set up properly, the avearage DS level at modems will be 0 dBmV with most devices falling between -8 to + 8 dBmV. Devices out of this range are usually caused by poor legacy installs with RG59 and cascaded splitters or drops from taps with high RF outputs going directly to the modem. Again, this a general statement, but most systems will run this way.

So just think about the statement that the optimum level should be -15 dBmV...you would have to lower your DOCSIS carriers (or the entire system!) by an average of 15 dB to achieve that level...funny stuff!

As far as US, generally most systems try to maintain TX levels between 35 and 50 dBmV. This is a general rule, and is vey dependant on your DOCSIS mode, modem types, CMTS configuration and carrier bonding.

I am concerned about your DS DOCSIS carriers set at 8 dB below analog. Are they 256 QAM? If so, with out knowing more about your system, in my humble opinion, those carriers should be 6 dB below analog at the very least.

As far as US. Are you running 16 or 64 QAM or a mixed mode 16/64 QAM carrier? If I remember correctly, the mixed mode can raise heck with some devices.

This is such a specific problem...when did this start? Was something changed recently? Anyway, I sent you a PM if you want to talk more.

Gary Muth
This is CABL.com posting #357614. Tiny Link: cabl.co/mbFb8
Posted in reply to: Recommended modem levels? by woodybeetle
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