4-7
Cisco uBR7200 Series Universal Broadband Router Hardware Installation Guide
OL-5421-03
Chapter 4 Connecting the Cisco uBR7200 Series Router to the Cable Headend
Connecting and Configuring the Downstream
Testing the Upconverter Output Level
If you are using a GI, Barco, or Scientific Atlanta upconverter, you can measure the 0 dBmV test point
at the
front
of the upconverter. If you are using a Vecima upconverter, you can measure the 0 dBmV test
point at the
back
of the upconverter. Your spectrum analyzer should display a signal similar to the one
shown in
Figure 4-5
.
Note
The digitally modulated carrier’s average power level should be set between 6 and 10 dB less than the
cable network’s video carrier amplitude.
Figure 4-5
shows a sample digital channel power measurement made on an Agilent 8591C spectrum
analyzer at a 44 MHz IF test point (North American headend).
Figure 4-5
Sample Digital Channel Power Measurement at 44 MHz IF Test Point
Setting the Upconverter Output Frequency
You must now select an output frequency. DOCSIS specifications permit channels from 91 to 857 MHz
(center frequency of 91 MHz is not required). In the example shown in
Figure 4-14
, a center frequency
of 610 MHz is used.
The following excerpts from the DOCSIS Radio Frequency Interface Specification define downstream
digitally modulated carrier frequencies.
•
DOCSIS — “The downstream frequency plan should comply with Harmonic Related Carrier (HRC),
Incremental Related Carrier (IRC), or Standard (STD) North American frequency plans per [IS-6].
However, operation below a center frequency of 91 MHz is not required.”
•
EuroDOCSIS — “The downstream frequency plan will include all center frequencies between 112
and 858 MHz on 250 kHz increments. It is up to the operator to decide which frequencies to use to
meet national and network requirements.”
Your output frequency should be in your narrowcast band of frequencies, or the narrowcast combiner.
Narrowcast frequencies are defined as frequencies that are transmitted to certain groups of fiber nodes
or regions in your network. (See
Figure 4-6
.) The same programming content is received within each
group of fiber nodes or regions. Different groups receive different content.
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