#### 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.)