Why is the aircraft radio always using the AM band instead of the FM band?

- Jan 07, 2019-

Wireless communication is essential for aircraft navigation in passenger aircraft and fighter aircraft. Due to the different motor performance and flight objectives of the two machines, a completely separate VHF band and UHF band are used. However, both aircraft can send and receive AM band radio broadcasts. Why does the aircraft radio use the AM band instead of the FM band?

Recently, wireless communication has also a digital mode, but still retains the FM band. On the other hand, the aircraft's use of the AM band in the air is mainly used as the wireless communication mode. Let us see why the aeronautical radio continues to use the AM band.

First, AM is the initial letter of amplitude modulation (amplitude modulation), a method of transmitting information by the intensity of radio waves. The disadvantage is that the sound quality is poor or weak compared to FM frequency modulation (frequency modulation).

However, the reason why the aircraft continues to use AM frequency wireless communication is that even if the weak radio wave is covered by strong radio waves, it will not be submerged. Even if multiple aircraft appear at the same frequency, the AM frequency is characterized by its transmission without being flooded by strong radio waves.


Moreover, the AM radio can hear weak radio waves from the back of strong radio waves when it is disturbed at night. The control tower can receive rescue communications for aircraft flying in the distance, while eliminating the danger of flying near the aircraft.

That is to say, the radio characteristic that is indispensable for the safe operation of the aircraft is the reason why the AM band continues to be used for air flight. In addition to this, the circuit configuration of the AM frequency radio is simple, and it is possible to transmit voice even in a narrow band.

Since aeronautical radio is a global system, it is not digitized. It is almost impossible to update the radio of all aircraft at the same time. In this sense, aircraft radio can be said to be usable for a long time.