An apparatus and a system, as well as a method and an article, may include operating a positive displacement motor having a pair of output orifices including a selectably movable outer output orifice disposed proximate to a fixed inner output orifice. Operation may include rotating the outer output orifice about the longitudinal axis of the motor when drilling fluid is flowing through the pair of orifices to control fluid pressure pulse amplitude from the outer output orifice. Additional apparatus, systems, and methods are disclosed.