The technical layout and initial results of an experiment to generate narrow-band, coherent, tunable terahertz (THz) radiation through the down-conversion of the frequency of optical lasers using a laser-modulated electron beam are described. In this experiment, a 120 MeV electron beam is first energy modulated by two lasers with different wavelengths. After passing through a dispersive section, the energy modulation is converted into a density modulation at THz frequencies. The central frequency of the THz modulation can be tuned by varying the wavelength of one of the two lasers or the energy chirp of the electron beam. The density-modulated beam will be used to generate narrow-band THz radiation using a coherent transition radiator inserted into the beam path. The experiment is being performed at the Next Linear Collider Test Accelerator (NLCTA) at SLAC, and will utilize the existing Echo-7 beamline, where echo-enabled harmonic generation (EEHG) was recently demonstrated. Show Partial Abstract