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Cisco uBR7200 Series Universal Broadband Router Hardware Installation Guide
OL-5421-03
Chapter 4 Connecting the Cisco uBR7200 Series Router to the Cable Headend
Measuring the RF Signal at the Forward Test Point on a Laser Transmitter
Note
The slight “ramp-up” at the beginning of the preamble when viewed in this mode is attributed to the time
required to charge the spectrum analyzer’s detector circuit.
Figure 4-55
shows a smooth and easily measured signal amplitude, providing accurate measurement of
a very fast burst upstream carrier. You can compare the measurements obtained using a spectrum
analyzer with those of specialized test equipment. In general, the readings from the spectrum analyzer
will be within 1 to 2 dB of the (more expensive) specialized equipment. Because 1 to 2 dB is well within
the calibration accuracy of spectrum analyzers, you can reliably use these procedures in the cable
headend environment.
Measuring the RF Signal at the Forward Test Point on a Laser
Transmitter
This section describes RF signal measurements that should be taken with a spectrum analyzer at the
downstream forward test point on the fiber-optic laser transmitter. (See
Figure 4-14 on page 4-15
for the
location of the downstream forward test point.)
Use the following steps to measure the downstream forward test point on the fiber-optic laser
transmitter:
Step 1
Connect the spectrum analyzer to the downstream forward test point on the fiber-optic laser transmitter.
Figure 4-56
shows a typical measurement of the downstream forward test point.
Figure 4-56
Measuring the RF Signal at the Downstream Forward Test Point on the
Laser Transmitter
Step 2
Using the spectrum analyzer zoom feature, zoom the display on the first individual video channel. In the
example in
Figure 4-57
, the first video channel is channel 48.
