Two examples of Langmuir waves observed by TDS on 13 June 2020. Panels a–c: Langmuir or beam-mode wave with a relatively broad spectral peak, while panels d–f: typical example of Langmuir waves with a narrow spectral peak. Panels a,d: waveforms of the three potentials from TDS. For these cases TDS provides three monopole potentials V_1 − 3 from each antenna. Panels b,e: waveforms of E_∥ and E_⊥. Panels c,f: power spectra of E_∥ and E_⊥. The blue and green vertical lines indicate f_pe calculated from n_e, SC and the frequency at which the power peaks f_pk.