Cisco Model GS7000 4-Port Node 1 GHz with 42 54 Split Installation Guide
Chapter 5 Using the Web Interface
64
4037424 Rev A
Downstream Data
Frequency — is the downstream frequency given in Hz.
Power — is the downstream power given in dBmV.
SNR / (RxMER) — this is the downstream signal quality. Modulation Error
Ratio (SNR).
Ratio (SNR).
EVM —Error Vector Magnitude calculated from MER.
CER Interval — Codeword Error Rate (CER) refresh rate.
Pre FEC CER — Codeword error rate (CER) BEFORE forward error correction is
applied.
applied.
Post FEC CER — Codeword error rate (CER) AFTER forward error correction is
applied.
applied.
Updates Remaining — this is the number of sample updates remaining for this
session.
session.
Interpreting QAM Constellation Data by Visual Inspection
The usefulness of the QAM constellation comes in the ability to recognize common
shapes and configurations within the map. The following table summarizes the
shapes commonly visible in the RF Constellation page. Examples of these shapes are
illustrated in the figures that follow.
shapes and configurations within the map. The following table summarizes the
shapes commonly visible in the RF Constellation page. Examples of these shapes are
illustrated in the figures that follow.
Shape
Focus
Impairment
Description
Individual cells
and entire QAM
constellation
and entire QAM
constellation
Normal
Dots are centered in the
individual QAM quadrants.
The QAM constellation has a
uniform square shape.
individual QAM quadrants.
The QAM constellation has a
uniform square shape.
Individual cells
Low CNR and/or
Low MER
Low MER
Individual cells of QAM
constellation contain a fuzzy
and diffused pattern.
constellation contain a fuzzy
and diffused pattern.