Cisco 7246 - uBR Router, Руководство по установке оборудования

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4-5
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
Setting the North American Upconverter Input Level
You must set the upconverter IF input level, according to the manufacturer’s instructions, to match the
downstream output level of the cable interface cards. Earlier Cisco cable interface card output was
+32 dBmV (+/–2 dB). More recently, however, Cisco cable interface cards feature an output rating of
+42 dBmV (+/–2 dB). Refer to the
“Measuring the Downstream RF Signal” section on page 4-16 and be
sure to check the documentation that accompanied your Cisco cable interface line card or the faceplate
of the cable interface line card itself to determine its downstream output level.
Depending on the upconverter model selected (see Appendix F, “Manufacturers for Headend
Provisioning Requirements,” for manufacturers and models), you might need to add attenuation between
the cable interface line card IF output and upconverter input to achieve the recommended input level to
the upconverter. For example:
• The recommended IF input to the General Instrument C6U is +23 dBmV; this upconverter requires
6 to 9 dB of attenuation on the input cable.
•
The IF input to the Vecima MA4040 is +33 dBmV; this upconverter requires no attenuation on the
input cable. (See
Figure 4-3 .)
To verify the input level, connect a spectrum analyzer to the test point on the upconverter input. If your
upconverter is equipped with a built-in meter, you do not need to connect a spectrum analyzer. The IF
input level at the test point should be 0 dBmV at 44 MHz.
Figure 4-3 Setting the North American Upconverter Input Level
Tip •
To adjust the General Instrument (GI) C6U to the correct level at the test point, use the Manual IF
Gain Control (MIGC) on the C6U to adjust the level until the output at the test point reads 0 dBmV
at 44 MHz on a spectrum analyzer, when +23 dBmV is present at the upconverter IF input.
• The test point on the GI upconverter has a +/-2 dB accuracy specification.
•
To adjust the Vecima MA4040 to the correct level at the test point, set the
Automatic Gain Control (AGC) to auto. The Vecima MA4040 has a built-in meter
to verify this setting.
Cisco uBR7200
series
Downstream output
44 MHz IF
+32 dBmV ( 2 dB)
+
-
6 dB to 9 dB attenuator
for GI upconverter
IF input
RF output
Upconverter
Spectrum analyzer
or meter at test point
should equal 0 dBmV
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