Technical data

www.westermo.com Theoretical and general applications 67
Modulation
Modem is a composite of the word modulation, i.e. signal conversion, and demodula-
tion, which is the regeneration of the original signal. The data signals must be convert-
ed and adapted in order to be transferred over different types of cable. The digital sig-
nal levels (ones and zeros) are converted to readable transformations for the chosen
cable. There are three basic types of modulation. Frequency modulation where differ-
ent frequencies are used to represent ones and zeros. Phase modulation utilises the
phase variation of a carrier to represent ones and zeros. Amplitude modulation utilises
the signal level, or amplitude peaks, to create readable ones and zeros. More complex
modulation techniques are created by combining the basic types.
Phase modulation
Frequency modulation
0 01 10100010
Amplitude modulation
B A C K