Upstream RF Troubleshooting

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Upstream Integrity • Verify that the upstream digitally modulated carrier amplitude at the input to the CMTS upstream port is within spec Upstream RF Troubleshooting A typical value is 0 dBmV, but this may vary depending on the CMTS manufacturer’s specs and CMTS configuration • Check the upstream carrier-to-noise, carrier-to-ingress, and carrier-tointerference ratios DOCSIS assumes a minimum of 25 dB for all three parameters © 2003, Cisco Systems, Inc. All rights reserved. 6
Digitally Modulated Carrier Amplitude • Because of the bursty nature of upstream digitally modulated carriers, it’s difficult to measure average power level Upstream RF Troubleshooting © 2003, Cisco Systems, Inc. All rights reserved. • The zero-span method is the easiest way to obtain an accurate amplitude measurement 7
Page 1 and 2: Upstream RF Troubleshooting © 2003
Page 3 and 4: CMTS Configuration • Check this f
Page 5: Check the Upstream at the CMTS Conn
Page 9 and 10: Check the Upstream at the CMTS Spec
Page 11 and 12: Upstream Constellations Poor carrie
Page 13 and 14: Upstream RF Impairments Stationary
Page 15 and 16: Upstream RF Impairments Multiplicat
Page 17 and 18: Thermal Noise Poor carrier-to-noise
Page 19 and 20: Intermodulation Distortion • An e
Page 21 and 22: Frequency Response • Defective co
Page 23 and 24: Microreflections • The reflected
Page 25 and 26: Microreflections Causes: • Kinked
Page 27 and 28: Microreflections • Here’s anoth
Page 29 and 30: Transit Delay (cont’d) • Signal
Page 31 and 32: Group Delay (cont’d) • Group de
Page 33 and 34: Group Delay vs. MER • QPSK typica
Page 35 and 36: Group Delay • Specialized test eq
Page 37 and 38: Upstream Over-The-Air Spectrum, 5-3
Page 39 and 40: Impulse Noise Upstream RF Troublesh
Page 41 and 42: Signal Clipping • RF ingress and
Page 43 and 44: Signal Clipping (cont’d) Noise ab
Page 45 and 46: Transient Hum Modulation • Ferrit
Page 47 and 48: Intermittent Connections Upstream R
Page 49 and 50: Still Having Problems? • If every
Page 51 and 52: Still Having Problems? • If CMTS
Page 53 and 54: Out in the Field… • Verify that
Page 55 and 56: A Few Potential Problems • Improp
Page 57 and 58:
DOCSIS 1.0 Assumed Upstream RF Chan
Page 59 and 60:
DOCSIS 1.1 Assumed Upstream RF Chan
Page 61 and 62:
Useful References—Magazine Articl
Page 63 and 64:
Useful References—Magazine Articl
Page 65 and 66:
Useful References—Books • Farme
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Upstream RF Troubleshooting

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