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Bah Humbug
The Boro
·Comcast Business..
·Cingular Wireless
reply to harald

Re: [Signals] Should SNR swing as much as 1dB with temperature?

said by harald:

No cable modem is capable of reading SNR.

What they display as SNR is a calculated value based upon the ratio of packets with correctable errors to good packets, using the formulas derived by Claude Shannon in the 1040's. The details of how this is done is proprietary to Broadcom and other chip makers. Inferences about what will cause the SNR to change are pretty shaky...

I have seen references to that as well, but that does not explain why Channel ID 6 in my SB6121 does not have a much higher DS SNR than the other three channels, instead of all of them reading 38dB.

A well-regulated militia, being necessary to the security of a free State, the right of the people to keep and bear arms shall not be infringed.

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Columbus, OH
What is missing is an understanding of what time frame is used for the calculation. Here is a white paper from Broadcom that explains the issues, but does not even hint at what the averaging parameters are:

»www.broadcom.com/collateral/wp/C ··· 01-R.pdf