3. Setting Laser Drive Levels
The HFC Enhance Return Path Transmitters for the NT/NB Nodes have been optimized based on the assumption that they
will be driven with 37 MHz of loading
(1)
.
12. The Return Path can be optimized by injecting a carrier at the node port of level “EXPECTED RETURN CARRIER LEVEL
+20 dB”
(Note: EXPECTED RETURN CARRIER LEVEL is a system specific design specification)
and adjust padding
in the return path until the level measured on the return transmitter’s -20 dB test point equals the value (in dBmV) that
is noted on the label beside the return path transmitter’s -20 dB RF test point. The label location is adjacent to the test
point on the transmitter as shown in Figure #2 below. The reverse pad locations for each port are shown in Figure #3
below. Further, there is a pad that is common to all ports in front of the transmitter in the optical lid.
(1)
The optimum operating point for the transmitter is selected as the point that is 5 dB above the location where the noise side of the
NPR curve crosses 41 dB. The NPR curve is generated using 37 MHz of noise loading and the per carrier power level is calculated
assuming that the total power is calculated at the optimum operating point is spread across 6 carriers.
Figure #2 Laser Drive Level Label
HFC Enhance
®
– NT/NB DFB Return Path Transmitter Installation & Operation Manual
Figure #3 NT/NB Node Overview
HFC Enhance
®
– NT/NB DFB Return Path Transmitter Installation & Operation Manual
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