  We derive the distribution of flux density of a compact source exhibiting
strong diffractive scintillation. Our treatment accounts for arbitrary spectral
averaging, spatially-extended source emission, and the possibility of intrinsic
variability within the averaging time, as is typical for pulsars. We also
derive the modulation index and present a technique for estimating the
self-noise of the distribution, which can be used to identify amplitude
variations on timescales shorter than the spectral accumulation time. Our
results enable a for direct comparison with ultra-high resolution observations
of pulsars, particularly single-pulse studies with Nyquist-limited resolution,
and can be used to identify the spatial emission structure of individual pulses
at a small fraction of the diffractive scale.
