Modes
The term mode has varying meanings, according to the context, but the most common are permitted modes in amateur licensing.
A mode is the way of changing electromagnetic waves, modulating them so that transmission of information is possible. There are three "true" modes, or methods of modulation: Amplitude Modulation (AM), Frequency Modulation (FM) and Continuous Wave (CW). Remaining modes are derived from these.
Continuous Wave (CW)
A continuous wave is an electromagnetic wave of constant amplitude and frequency, a pure carrier, and information is carried by turning the wave on and off, and measuring the interval. Morse code is often transmitted using CW.
See http://en.wikipedia.org/wiki/Continuous_wave
Amplitude Modulation (AM)
The transceiver produces a carrier wave at the frequency of transmission. Voice is superimposed on the carrier wave, and alters its shape by changing the Amplitude or height of the wave. Hence the frequency and wavelength of the carrier do not change with this form of modulation.
See http://en.wikipedia.org/wiki/Amplitude_modulation
Frequency Modulation (FM)
The transceiver produces a carrier wave, in the same way as for Amplitude Modulation. In this case however, voice is added to the carrier so that is frequency changes. This in turn affects the wavelength of the carrier, but the amplitude remains constant.
See http://en.wikipedia.org/wiki/Frequency_modulation
Lesser known modes
- Phase modulation (PM). In this mode the phase (its position relative to a central axis) of the carrier is changed by the audio signal.
- Quadrature amplitude modulation (QAM). In this mode, two carrier waves, 90° out of phase with each other are produced. QAM is a variant of AM, but both carriers are modulated by the audio signal.
Digital modes
The licensing regime defines digital modes as those modulation techniques that require digital data processing. In Australia refer to the ACMA LCD ( Licence Conditions Determination) for exact details. You will need to scroll down the page to find the link.
Technically, whenever a signal is turned on and off to enable transmission of information, it can be considered to be a digital mode. Under this definition, CW is certainly a digital mode. This section refers to methods of transmitting and receiving (rather than modulating) that are digital, or that require digital processing in part of the transmission or receiving process.