  We present a stabilization technique developed to lock and dynamically tune
the resonant frequency of a moderate finesse Fabry-P\'erot (FP) cavity used in
precision atom-cavity quantum electrodynamics (QED) experiments. Most
experimental setups with active stabilization either operate at one fixed
resonant frequency or use transfer cavities to achieve the ability to tune the
resonant frequency of the cavity. In this work, we present a simple and
cost-effective solution to actively stabilize an optical cavity while achieving
a dynamic tuning range of over 100 MHz with a precision under 1 MHz. Our unique
scheme uses a reference laser locked to an electro-optic modulator (EOM)
shifted saturation absorption spectroscopy (SAS) signal. The cavity is locked
to the PDH error signal obtained from the dip in the reflected intensity of
this reference laser. Our setup provides the feature to efficiently tune the
resonant frequency of the cavity by only changing the EOM drive without
unlocking and re-locking either the reference laser or the cavity. We present
measurements of precision control of the resonant cavity frequency and vacuum
Rabi splitting (VRS) to quantify the stability achieved and hence show that
this technique is suitable for a variety of cavity QED experiments.
