Cisco 7246 - uBR Router, Руководство по установке оборудования

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4-13
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
Figure 4-12 Increased Frequency Resolution on IF Input Sweep and RF Output Sweep
Note
This step displays an even greater resolution for both the IF input and RF output signals at your
upconverter.
Fine-Tuning the Center Frequencies
The signals in Figure 4-12 feature a very slight frequency error. Continue with the final steps in this
procedure to resolve this frequency error and display the low-frequency additive phase noise at and
below 10 kHz.
Step 1
Eliminate the offset between the IF and RF output traces by fine-tuning the RF output center frequency
on the spectrum analyzer. The difference between the center frequencies in these two signals is referred
to as the “frequency error” of the upconverter.
Note
The FCC specifies that the frequency error of an upconverter cannot exceed 5 kHz in the aviation bands.
Step 2
Repeat Step 3 and Step 4 under the “Viewing the RF Output Signal” section on page 4-11 , substituting
the exact center frequency for 555 MHz. In the example, the exact center frequency is 544.99970 MHz.
Your analyzer should display a signal similar to the one shown in
Figure 4-13 .
Note
Your spectrum analyzer must feature frequency counting capability in order for you to be able to work
out the new, adjusted center frequency.