AM is Amplitude Modulation.. aviation Frequencies are FM, which is short for Frequency modulation. Mhz is Mega Hertz, a measurement of how Frequent the wave passes through each faze. Modulation is another word for change, so as you Modulate the Frequencies you are changing them, as in changing the station, channel or Frequency. Aviation frequencies are the same as regular radio stations, just starting around 120.00 Mhz and going up, they use VHF and military mostly uses UHF for very high frequency and ultra high frequency... all still Frequency Modulation, or FM.