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The problems with bandpass filtering a high frequency modulated data
signal can be eliminated if the pulse shaping is performed on the baseband input data
stream, and a linear modulation process employed which preserves the amplitude information
of the data signal. Using the mixer-based approach the baseband data stream can be pre-filtered using a low pass (root raised cosine) filter and this pulse shaping information will be imposed (assuming the mixer is sufficiently linear) as the envelope variation of the carrier. |
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In practical terms, linear active integrated mixers capable of operating at carrier frequencies up to several GHz are now readily available off the shelf, costing only a few dollars (see in-depth.) |