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Setting simulation parameters for digitally modulated signals is quite different than the considerations for a CW signal. First, the maximum offset frequency is dependent on the modulation bandwidth, not the phase noise mask. The maximum offset frequency can be set to one-half the modulation bandwidth. Next, the sampling frequency should be set to at least 4 times the maximum offset frequency (not 2 times as for the CW case). Next, the minimum offset frequency can be set somewhat higher than the minimum mask offset frequency due to the roll-off affect from the ALIGN blocks. Note: for BER systems the ALIGN block is often not used in which case the roll-off effect does not take place and the minimum offset frequency should be set lower.
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