  The remarkably strong radio gravitational lens PKS 1830-211 consists of a one
arcsecond diameter Einstein ring with two bright compact (milliarcsecond)
components located on opposite sides of the ring. We have obtained 22 GHz VLBA
data on this source to determine the intrinsic angular sizes of the compact
components. Previous VLBI observations at lower frequencies indicate that the
brightness temperatures of these components are significantly lower than 10E10
K, less than is typical for compact synchrotron radio sources and less than is
implied by the short timescales of flux density variations. A possible
explanation is that interstellar scattering is broadening the apparent angular
size of the source and thereby reducing the observed brightness temperature.
Our VLBA data support this hypothesis. At 22 GHz the measured brightness
temperature is at least 10E11 K, and the deconvolved size of the core in the
southwest compact component is proportional to the wavelength squared between
1.3 cm (22 GHz) and 18 cm (1.7 GHz). VLBI observations at still higher
frequencies should be unaffected by interstellar scattering.
