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They show digital FM Coder based on ADSP2181 and a direct modulation with a DDS chip to 1/3 of the base frequency of fm band. the third harmonic lies within 89-108MHz.
So it works completely digital. by adding a SPDIF receiver you can build up a professional fm coder with very high quality. (if calculation power of the DSP is enough, you can even add a limiter for analog signal.)