An oscillating shear valve system for generating pressure fluctuations in a flowing
drilling fluid comprising a stationary stator and an oscillating rotor, both with
axial flow passages. The rotor oscillates in close proximity to the stator, at
least partially blocking the flow through the stator and generating oscillating
pressure pulses. The rotor passes through two zero speed positions during each
cycle, facilitating rapid changes in signal phase, frequency, and/or amplitude
facilitating enhanced, multivalent data encoding. The rotor is driven by a motorized
gear drive. In one embodiment, a torsional spring is attached to the motor and
the resulting spring mass system is designed to be near resonance at the desired
pulse frequency. The system enables the use of multivalent encoding schemes for
increasing data rates.