New electronics for the multichannel far infrared tangential interferometer/polarimeter system employed on the National Spherical Torus Experiment (NSTX) have greatly extended its capability to monitor high frequency density fluctuations. Such measurements are essential in understanding transport physics issues in NSTX as well as for the coming ITER device. The electronics, which were previously limited to ∼250 kHz, have been upgraded with a video bandwidth that extends to 4 MHz when operating as an interferometry-only configuration, and to ∼500 kHz when operating as a simultaneous interferometer/polarimeter system. Experimental details and test results of the new electronics are presented.