Page 433 - PPL BEG-engelsk

Communication

4.13.2 Waveforms and modulation

The shapes and properties of waves are called waveforms.

Modulation is the process of changing a signal to transmit information.

In communication systems, modulation is used to combine a low-frequency

signal (such as sound) with a high-frequency carrier signal so that it can be
transmitted efficiently over long distances.

4.13.2.1 N0N

The NON signal is just a carrier wave. It can be heard

as a hiss if you listen to the frequency.

4.13.2.2 A1A

It wasn't long before people figured out how to code using radio signals.

Initially, this was done by interrupting the

transmission with intervals of size, like a dot or a

dash in the Morse code system.

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.

Flight Theory PPL(A)(UL)/LAPL Henning Andersen, Midtjysk Flyveskole© marts 2026 433