Radio Experimenter Theory Notes

Modulation

To modulate a signal or carrier means to somehow modify it in order to carry some form of intellegence. A transmitter sending out a signal, does just that. It sends out a carrier which can be detected by a receiver. As it stands, this system would be fairly useless for most applications. However, if we could change this carrier in some way to contain information we are said to modulate the signal.

The simplest way of doing this is to switch on and off the transmitter in a way which represents information. This is called continuous wave or CW and is used to send and receive Morse Code. The transmitter is keyed (switched on and off) using long and short pulses in various combinations representing the letters of the alphabet, numbers and punctuation. The receiver which detects the signal is then to switch on and off a light or more commonly generate a sound in sympathy with the transmitter.

CW is the simplest and oldest way of communicating intellegence via radio and is still quite popular among radio amateurs/experimenters to this day. However, if we want to send more complex information such as voice, data or images then more complex methods of modulation are required. The most common of these are Amplitude Modulation (AM), Frequency Modulation (FM) and Single Sideband (SSB). Of course, these are not the only methods of modulating a carrier but they are the principle ones and the ones that we are going to deal with in this course.

Continue to Amplitude Modulation  >>>

| Amplitude Modulation (AM) | Frequency Modulation (FM) | Single Sideband (SSB) |