  Uncertainty principles for concentration of signals into truncated subspaces
are considered. The ``classic'' uncertainty principle is explored as a special
case of a more general operator framework. The time-bandwidth concentration
problem is shown as a similar special case. A spatial concentration of radio
signals example is provided, and it is shown that an uncertainty principle
exists for concentration of single-frequency signals for regions in space. We
show that the uncertainty is related to the volumes of the spatial regions.
