vimwiki/tech/Modulation.wiki

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= Modulation =
Modulation is the altering of a carrier signal to add infomration. This is done
in everything from raido, to Ethernet.
== Bandwidth ==
Bandwidth is the amount of frequencies that a signal occupies. For example, the
Human voice can make frequencies from 300Hz to 3000Hz, therefore having a
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bandwidth of 3000 - 300 = 2700Hz.
== Types of Modulation ==
=== CW ===
Bandwidth: 150hz
Continuous Wave of CW is a type of signal where the pulsing of the signal
encoded information, instead of modifying the carrier signal. An example of
this is Morse code. Due to how concentrated the signal is, CW is used for
extreme ranges.
=== AM ===
Bandwidth: 6khz (voice); 10khz (broadcast)
Amplitude Modulation of AM is a form of modulation where the amplitude of the
signal is changed to encode information. The signal as a result will take up
space both above and below the carrier, called Upper Side Band (USB) and Lower
Side Band (LSB).
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AM has a Peak Envelope Power. This is determined by the max power of the
transmitter, and the Mic gain.
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=== SSB ===
Bandwidth: 2-3khz (voice); 500-3000hz (digital)
Single Side Band (SSB) Is when an AM signal is encoded by only modulating one
part of the signal, and leaving the other unchanged. This allows for less
bandwidth use for the same information.
Due to SSB concentrating the same amount of power for the signal into a
narrower portion of the signal, it is often used for long distance VHF and UHF
(see [[frequency_range]]).
Standards have formed around SSB, and wether to use USB or LSB on different
frequencies. If < 10Mhz, LSB. Else if >= 10Mhz, USB.
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SSB has a Peak Envelope Power. This is determined by the max power of the
transmitter, and the Mic gain.
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=== FM/PM ===
Bandwidth: 10-15khz (voice); 150khz (broadcast)
Frequency Modulation (FM) and Phase Modulation (PM) are two similar types of
modulation where the signal is encoded by changing either the frequency of the
signal, or the phase of the signal.
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Because FM/PM does not change in amplitude, the power output is fixed.
Therefore, the PEP is fixed as well.
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== QAM ==
Quadrature Amplitude Modulation. See [[QAM]]
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=== Digital ===
There are several different types of digital signals, all determined by their
corresponding protocol.
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== Overmodulation ==
Over modulation or splattering is when the signal is to heavily modulated,
making it use to much bandwidth. This is generally negative, and can often be
fixed by speaking softly, changing mic gain, or moving away from the mic.
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The sound it makes to the reciever is a 'breaking up' sound, where distortion
occours on voice peaks.