Appendix C Using Modulated Carriers - Harmonic PWRLink II 4100S Series Product Manual

This appendix provides information about setting up PWRLink™ II 4100S
Series Optical Transmitters for use with modulated carriers.
PWL 4100S transmitters are adjusted at the Harmonic factory for specified
CNR, CSO and CTB using NTSC unmodulated carriers.
When the carriers are modulated:
• The average power of the modulated carrier is about 2 dB lower than the
unmodulated carrier.
• Sideband signals are generated and the carrier level is reduced. The
average carrier level is about 3 dB lower than the unmodulated carrier.
• There will be a period when the carrier is not being modulated, so that
the peak value of the modulated carrier is the same as that of the
unmodulated carrier.
When setting up the transmitter with modulated carriers, there are typically
two different objectives, as described in the two sections below. You need to
choose the objective that best fits your system requirements.
Objective 1
When following Objective 1:
• The goal is to achieve the maximum possible modulation, with better
CNR by about 2 dB compared to unmodulated carriers.
• Average CSO and CTB will be the same as the unmodulated case. Higher
CSO and CTB occur occasionally, for brief instants.
This objective can be achieved by setting up the transmitter with modulated
carriers in CW mode when running Autosetup. See Figure C-1 on page C-3.
Remember that the modulated carriers are about 2 dB lower in average RF
power. This is what the transmitter's built-in detector will determine. The
transmitter responds to this drop at the detector by setting the pad 2 dB lower
than the factory optimized setting.
In this case, the average input RF power is adjusted to be the same as in the
unmodulated carrier. However, the carrier peak level is about 2 dB higher.
Thus, the CNR is typically 2 dB better in this scenario than in the case of
unmodulated carriers.
PWRLink™ II 4100S Series Optical Transmitter Product Manual Rev A (3/06)
Using Modulated Carriers
Appendix C
C–1