Although TX performance has mainly been focused on 3rd order IMD performance, produced by a two tone test, there are several other characteristics which can be just as harmful to the transmitted signal.
Other things we should be looking at:
- ALC overshoot
- Phase noise
- Key clicks
Understanding these issues can be difficult. Rob Sherwood has done a great job of describing these in his BARC 2009 presentation.
Due to too short rise times, key clicks can be just as bad as IMD, and are part of the reasons the bands are so full today.