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Communication
A1A signals are an interrupted carrier wave. A1A
cannot be heard unless the receiving equipment is
equipped with BFO, which is a special device that
puts sound on where there is no carrier wave.
Old radio beacons can broadcast A1A identification.
4.13.2.3 A2A and low-frequency tone
Inventive people figured out how to send audible tones.
In A2A, the amplitude height of
the carrier wave is modulated
with a low-frequency tone.
This is called amplitude
modulation (AM).
The audible tones have a lower frequency than the carrier wave.
4.13.2.4 A3E
A3E is the name of the waves we transmit
when we talk on the radio from an airplane.
It is not far from modulating the amplitude
with an audible tone to modulating it with
speech. All that is required is a microphone.
4.13.2.5 F3E / FM
This way of modulating is called frequency modulation (FM).
Here the amplitude is
constant, but the frequency
changes.
These waves are called F3E and are used for vehicle communication.
Flight Theory PPL(A)(UL)/LAPL Henning Andersen, Midtjysk Flyveskole© 2025 432
