As discussed earlier, a goal of communications is to use a carrier frequency
as the basic frequency of a communication, but to modify it by using a process
called modulation to encode information onto the carrier wave
.
There
are three aspects of the basic carrier wave that can be modulated:
- Amplitude
- Frequency
- Phase or angle
The three corresponding techniques are as follows:
- Amplitude modulation (AM)
- Frequency modulation (FM)
- Phase modulation (PM)
Most communication systems use some form or combination of these three
basic modulation techniques.
Extreme cases of these techniques include
the following:
-
Amplitude shift keying (ASK) – Turning the amplitude all the way off
-
Frequency shift keying (FSK) – Hopping to an extreme frequency
-
Phase shift keying (PSK) – Shifting the phase 180 degrees
Use the interactive activity to see how a zero or a one can modulate an
analog carrier signal, in each of these techniques.