In some embodiments, an ex-situ apparatus and a system, as well as a method and an article, operate to transmit wideband modulated pulses to generate an externally-projected oscillating magnetic field in a material body, to record one or more raw echo free induction decay (REFID) signals during echo acquisition periods following some of the second modulated pulses, and to transform the acquired REFID signals via frequency decomposition to determine a preferred nuclear magnetic resonance frequency associated with a maximum amplitude of decomposed frequency components. Additional apparatus, systems, and methods are described.