Â© 2014 SPIE. We present an ongoing effort to achieve a Double Fourier Modulating (DFM) interferometer in the thermal infrared wavelength range. We describe a testbed designed to combine a sky simulator in the form of a miniaturized complex calibration source at the focus of a parabolic collimator with an interferometer baseline consisting of two parallel telescopes each mounted on a motorized linear stage. The two input arms are combined after one of them is modulated via a fast-scanning piezoelectric roof-top mirror. The optical design and layout of the testbed, the choice of interferometer parameters as well as the calibration scene adopted as source are described.