Two typical in situ acquired RPC-MIP mutual impedance spectra (after compensation of instrumental effects such as interferences and solar wind response removal) in the ionosphere of 67P, from which the electron plasma frequency, f_p, (shown by a vertical black line) is obtained, both in a plasma dominated by a warm electron population and characterized by a single resonance (left panel), and in a plasma characterized by a mixture of warm and cold electron populations and characterized by a double resonance (right panel). For the first (resp. second) spectrum, f_p = 274 kHz (resp. f_p = 421 kHz) corresponding to n_e = 924 cm⁻³ (resp. n_e = 2198 cm⁻³). These two spectra have been measured with the RPC-MIP phased SDL sub-mode.