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Cisco uBR7225VXR Universal Broadband Router Hardware Installation Guide
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Chapter4 Connecting the Cisco uBR7225VXR 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 4-43 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 2dB 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.
Use the following steps to measure the downstream forward test point on the fiber-optic laser transmitter:
Step1 Connect the spectrum analyzer to the downstream forward test point on the fiber-optic laser transmitter.
Figure 4-44 shows a typical measurement of the downstream forward test point.
Figure4-44 Measuring the RF Signal at the Downstream Forward Test Point on the
Laser Transmitter
Step2 Using the spectrum analyzer zoom feature, zoom the display on the first individual video channel. In the
example in Figure 4-45, the first video channel is channel 48.