First, let me paste this whitepaper link:
"Implementation of 16-QAM to Increase the Value of Cable Modems"
http://www.cisco.com/en/US/tech/tk86/tk319/technologies_white_paper09186a0080237c17.shtml
and now let me quote a part of it:
Most systems exhibit low frequency noise below 20 MHz, especially in the 5 to 15 MHz range.
These are some frequencies in which you should avoid placing the upstream digitally modulated carrier:
<20 MHz—Low frequency electrical noise and ingress.
27 MHz—Citizens band (CB) radio.
28 MHz—10-meter amateur radio band.
>38 MHz—Group delay issues from amplifier diplex filters.
Increments of 6 MHz (that is, 6 MHz, 12 MHz, 18 MHz, 24 MHz, 30 MHz, 36 MHz, 42 MHz), because of the possibility of CPD
My Problem:
I am fighting a losing battle trying to convince peers that one of our problems is we are not following whitepapers put out from a vendor. Now, while the CMTS doesn't report precise SNR, it's a pretty good indication of what is happening on that upstream. We graph SnR via MRTG, and it really looks like a heart beat (SNR jumps from low teens to high 20's and back and I can see this in a sh controller for the cable interface) but realworx shows nothing (or so I am told) .. When I change the frequency on the upstreams from 30 or 36 to say 31 or 34.4 the graphing from the CMTS side just smoothes out.
My Questions:
So are there any thoughts as to the validity of this, mainly, the part of the CPD and avoiding the centering on lower 6MHz increment frequencies?
what is the typical upstream frequency you center on?
CMTS Upstream Frequencies
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