A spectrometer named Radiation Explorer in the Far InfraRed (REFIR) is being proposed for a future space mission aimed at the spectral measurement in the far infrared of the Earth outgoing emission, with particular attention at the spectral regions that are not covered by any current or planned space mission. The instrument requirements include continuous operation in the spectral range of 100-1100 cm-1 with a resolution of 0.5 cm-1, 6.5 s acquisition time, signal-to-noise ration better than 100 in the ranges 400-600 and 650-800 cm-1 and an accuracy of absolute calibration better than 0.5 K at 280 K at least in the range 400-650 cm-1. To meet these requirements, a spectrometer based on a polarising interferometer with a new optical configuration has been designed. The main characteristics include dual input and output ports, optics of the interferometer with full tilt compensation, and measurement of both planes of polarisation of the source on a single detector. In preparation for a possible space mission, a BreadBoard version (REFIR/BB) of the Fourier transform spectrometer has been built. REFIR/BB will allow us to study the trade-off between all instrument parameters, to test the optical layout and to optimise the data acquisition strategy. In perspective the breadboard could be flown for test flight on aircraft or balloon platforms. This paper describes REFIR/BB characteristics and preliminary experimental results with particular attention to the acquisition strategy and the instrument characterisation. Tests were performed both in air, at ground level, and under vacuum.