Two different methods for the creation of low-frequency waves in the drift plasma frequency range () have been investigated in the TAU-1 device. The first method is based on the beat process between two initially excited oblique Langmuir waves, when the frequency of the beat wave is near the draft plasma frequency. The second method is based on the modulation of the initial excited oblique Langmuir wave by a low-frequency signal . The shape of the frequency spectra is significantly modified by the presence of the externally excited waves.