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Radio signal modulation
A radio signal comprises two parts:
- the message (information)
- the frequency for transmission of the information (the carrier)
The process of adding information (an audio signal) to a carrier is called modulation.
Amplitude modulation (AM)
The message is combined with a carrier on a set frequency.
When the message is added to the carrier wave, the amplitude of the wave form varies depending on the volume of the audio signal.
Frequency modulation (FM)
Again the audio signal is combined with a carrier on a set frequency however the amplitude of the resulting signal remains constant. The freequency changes relative to the volume of the audio signal. When the volume of the audio signal is louder, the waves are closer together. In other words, the frequency of the waves per second increases.
Continuous wave modulation (CW - Morse code)
A continous wave has a constant amplitude and frequency. To send information you simply switch this wave on and of. When it is on, the radio wave is transmitted. When it is off, nothing is transmitted.
This is the basis for communication using Morse code over radio waves.