  Atmospheric water vapor causes significant undesired phase fluctuations for
the Submillimeter Array (SMA) interferometer, particularly in its highest
frequency observing band of 690 GHz. One proposed solution to this atmospheric
effect is to observe simultaneously at two separate frequency bands of 230 and
690 GHz. Although the phase fluctuations have a smaller magnitude at the lower
frequency, they can be measured more accurately and on shorter timescales due
to the greater sensitivity of the array to celestial point source calibrators
at this frequency. In theory, we can measure the atmospheric phase fluctuations
in the 230 GHz band, scale them appropriately with frequency, and apply them to
the data in 690 band during the post-observation calibration process. The
ultimate limit to this atmospheric phase calibration scheme will be set by the
instrumental phase stability of the IF and LO systems. We describe the
methodology and initial results of the phase stability characterization of the
IF and LO systems.
