Comparison of the measured receiver power spectral density with the theoretical received power. Upper: for the sensor V1-V2, as a function of the frequency, calculated from the minimum background. Black dots represent the data points. Lower: daily minima of the HFR spectra minus as a function of the frequency, over the time span March 1-December 31, 2020 for the sensor V1-V2. Red solid line represents the theoretical receiver power, expected for the model Novaco & Brown (1978), as obtained from Equations (8), (A.1),(A.2) using Γl_eff = 3.4 ± 0.1 m (from the galactic background measurements). The increase of the measured voltage spectral power at frequencies above 4 MHz is the consequence of the antenna resonance.