High resolution FT rotational spectroscopy of gases in the decimeter spectral region with a heterodyne detection system, that uses the Fabry-Perot resonator and supersonic jet for the maximal sensitivity and resolving power, is introduced as a unique tool for the conformational analysis of complex molecules. The paper describes technical spe¬cifications of the new FTMW spectrometer recently built up at the Institute of Chemical Technology, Prague.