B-4
Cisco uBR7225VXR Universal Broadband Router Hardware Installation Guide
OL-17309-02
AppendixB RF Specifications
DOCSIS 1.1 Transmission Characteristics
DOCSIS 1.1 Transmission Characteristics
The following tables provide information on the assumed downstream RF channel transmission
characteristics for DOCSIS 1.1.
Downstream RF Channel Transmission Characteristics
Transmission is from the headend combiner to the cable modem input at the customer location.
Measurement methods are defined in NCTA or CableLabs2 documentation.
Go to the following URL: http://www.ncta.com/. Search on “transmission”.
Go to the following URL: http://www.cablelabs.com/.
TableB-5 DOCSIS 1.1 Assumed Downstream RF Channel Transmission Characteristics
Parameter Value
Frequency range Cable system normal downstream operating range is from
50 MHz to as high as 860 MHz. However, the values in this
table apply only at frequencies ≥ 88 MHz.
RF channel spacing (design bandwidth) 6 MHz
Transit delay from headend to most distant customer ≤ 0.800 msec (typically much less)
Carrier-to-noise ratio in a 6-MHz band Not less than 35 dB1
1. Measured relative to a QAM signal that is equal to the nominal video level in the plant.
Carrier-to-composite triple beat distortion ratio Not less than 41 dB1
Carrier-to-composite second order distortion ratio Not less than 41 dB1
Carrier-to-cross-modulation ratio Not less than 41 dB1
Carrier-to-any other discrete interference (ingress) Not less than 41 dB1
Amplitude ripple 3 dB within the design bandwidth
Group delay ripple in the spectrum occupied by the CMTS 75 ns within the design bandwidth
Micro-reflections bound for dominant echo –10 dBc @ ≤ 0.5 microseconds
–15 dBc @ ≤ 1.0 microseconds
–20 dBc @ ≤ 1.5 microseconds
–30 dBc @ >1.5 microseconds
Carrier hum modulation Not greater than –26 dBc (5%)
Burst noise Not longer than 25 microseconds at a 10-Hz average rate
Maximum analog video carrier level at the cable modem input 17 dBmV
Maximum number of analog carriers 121