  An empirical Compton up-scattering model is described which reproduces both
the fractional amplitude (RMS) vs. energy and the soft time lags in the 830 Hz
QPO observed in 4U1608-52 on Mar. 3, 1996. A combination of two coherent
variations in the coronal and soft photon temperatures (with their relative
contributions determined by enforcing energy conservation) gives rise to the
QPO's energy dependent characteristics. All input parameters to the model, save
a characteristic plasma size and the fraction of Comptonized photons impinging
on the soft photon source, are derived from the time-averaged photon energy
spectrum of the same observation. Fits to the fractional RMS and phase lag data
for this kilohertz QPO imply that the spatial extent of the plasma is in the
range from 4 to 15 km.
