4.0 Managing the SMG, Continued
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018-354-B0-001, Rev. A (05/2018)
Constellation Page
The Constellation page provides a constellation view of the DOCSIS channel that may assist in identifying and
troubleshooting common network impairments.
The page will automatically refresh until the samples remaining counter reaches 0. Clicking the Restart button refreshes
the constellation tool, and clicking the Stop button halts the analysis.
The number of samples can be changed from 100 (default) on the sampling control to either 150 or 50 for more or less
sample rates.
Fig. 4-10, QAM Constellation Tool
The tables on the right hand side of the screen provide a summary of common parameters associated with QAM
Constellation analysis. Here’s a breakdown of the parameters listed:
• Frequency - The tuned downstream frequency given in MHz.
• Power – Downstream power given in dBmV.
• SNR / (RxMER) – Downstream signal quality. Modulation Error Ratio (SNR)
• EVM – Error Vector Magnitude (from hardware MER (Modulation Error Ratio) / software MER).
• CER Interval – Codeword Error Rate (CER) refresh rate.
• Pre FEC CER – Codeword Error rate (CER) BEFORE forward error correction is applied.
• Post FEC CER – Codeword Error rate (CER) AFTER forward error correction is applied.
