In-depth

 

Baseband filtering method

 

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.
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.)