Modes: Difference between revisions
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The term mode has varying meanings, according to the context, but the most common are permitted modes in amateur licensing. | 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. | Waves have three characteristics that can be changed, Amplitude, Frequency and Phase. A mode is the way of changing electromagnetic waves, '''modulating''' them so that transmission of information is possible. Modulating signals can be either analogue, for example sound or digital. | ||
== | == Analogue Modulation methods == | ||
There are two main '''analogue''' modes, or methods of modulation: Amplitude Modulation (AM), Frequency Modulation (FM). Single Sideband (SSB) is a variant of AM. Tho final analogue mode, Phase modulation (PM) is rarely used in amateur stations. | |||
== Amplitude Modulation (AM) == | == Amplitude Modulation (AM) == | ||
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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. | 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 | See [http://en.wikipedia.org/wiki/Amplitude_modulation Amplitude Modulation] for more information. | ||
== Frequency Modulation (FM) == | == Frequency Modulation (FM) == | ||
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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. | 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 | See [http://en.wikipedia.org/wiki/Frequency_modulation Wikipedia Frequency Modulation] for more information. | ||
== Lesser known modes == | == Lesser known modes == | ||
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* 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, in which both carriers are modulated by an 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, in which both carriers are modulated by an audio signal. | ||
== Digital | == Digital modulation == | ||
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. | 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. | ||
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'''What do digital modes sound like?''' [http://www.kb9ukd.com/digital/ Click here to find out.] | '''What do digital modes sound like?''' [http://www.kb9ukd.com/digital/ Click here to find out.] | ||
== 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 Wikipedia Continuous Wave] for more information. | |||
== Amplitude Shift keying (ASK) == | |||
The amplitude of the carrier is varied according to a digital signal. | |||
See [http://en.wikipedia.org/wiki/Amplitude-shift_keying Wikipedia Amplitude Shift Keying] for more information. | |||
== Frequency Shift Keying == | |||
The frequency of the carrier is variued according to a digital signal. | |||
See [http://en.wikipedia.org/wiki/Frequency-shift_keying Wikipedia Frequency Shift Keying] for more information. | |||
== Phase Shift Keying (PSK) == | |||
The '''phase''' of the carrier is modunalted by a digital signal. In its simples terms,. this could mean for example that the phase of the carrier is turned through 180° with each change in the disigal signal. In practical terms, PSK allows long distance communication even when noise level are high. | |||
See [http://en.wikipedia.org/wiki/Phase-shift_keying Wikkipedia Phase Shift Keying] | |||
[[APRS]] | [[APRS]] | ||
== Digital modes in practice == | |||
The licensing regime defines digital modes as those modulation techniques that require digital data processing. In Australia refer to the [http://www.acma.gov.au/WEB/STANDARD/pc=PC_1256 ACMA LCD] ( Licence Conditions Determination) for exact details. You will need to scroll down the page to find the link. | |||
[[Digital Modes]] | [[Digital Modes]] | ||
Revision as of 13:53, 14 February 2008
The term mode has varying meanings, according to the context, but the most common are permitted modes in amateur licensing.
Waves have three characteristics that can be changed, Amplitude, Frequency and Phase. A mode is the way of changing electromagnetic waves, modulating them so that transmission of information is possible. Modulating signals can be either analogue, for example sound or digital.
Analogue Modulation methods
There are two main analogue modes, or methods of modulation: Amplitude Modulation (AM), Frequency Modulation (FM). Single Sideband (SSB) is a variant of AM. Tho final analogue mode, Phase modulation (PM) is rarely used in amateur stations.
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 Amplitude Modulation for more information.
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 Wikipedia Frequency Modulation for more information.
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, in which both carriers are modulated by an audio signal.
Digital modulation
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.
What do digital modes sound like? Click here to find out.
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 Wikipedia Continuous Wave for more information.
Amplitude Shift keying (ASK)
The amplitude of the carrier is varied according to a digital signal.
See Wikipedia Amplitude Shift Keying for more information.
Frequency Shift Keying
The frequency of the carrier is variued according to a digital signal.
See Wikipedia Frequency Shift Keying for more information.
Phase Shift Keying (PSK)
The phase of the carrier is modunalted by a digital signal. In its simples terms,. this could mean for example that the phase of the carrier is turned through 180° with each change in the disigal signal. In practical terms, PSK allows long distance communication even when noise level are high.
See Wikkipedia Phase Shift Keying APRS
Digital modes in practice
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.