non c'entra niente
io mi riferisco al fatto che certe frequenze insieme a certe modulazioni sono più adatte a fare una cosa piuttosto che un altra ( e non parlo di normali comunicazioni radio )

Radio wave experiments have been conducted at Arecibo, Puerto Rico and Gakona, Alaska together with numerical analyses aimed at investigating man-made and naturally-occurring ionospheric plasma turbulence. Research progress and results reported include the following. (1) Ionospheric ELF and VLF experiments in Alaska discover that a horizontal Hertzian magnetic dipole (HMD)) with a radius of about 7 km at an altitude around 70 km is responsible for the generation of ELF/VLF waves. (2) Numerical analyses of ELF and VLF wave generation show that the modulation scheme using the half-wave rectified wave is the most efficient one to generate signals at the modulation frequency and second harmonic, confirming our theoretical predictions. (3) Theoretical study of ionospheric HF heating experiments finds that the dominant factors, determining the number of cascade lines in the radar-detected spectrum of HF enhanced plasma lines (HFPLs), include the ion-to-electron temperature ratio, Ti/Te, the background plasma inhomogeneity scale length, and the heating wave field intensity. (4) The very intense ionospheric plasma turbulence observed over Arecibo, Puerto Rico on December 26, 2004 was possibly triggered by the tsunami-induced gravity waves propagating from Sumatra, Indonesia to Puerto Rico about 23 hours after the occurrence of a Mw = 9.2 earthquake.