Modulation is the method of taken your voice or any other sound and putting it into a radio signal that can be transmitted and understood by other people using the same radio equipment as you, that’s basically how radio modulation is explained.
Now for the techie stuff………
In CB radio you will come across a few types of modulation with the main ones being AM, FM and SSB, here is a quick guide to how they work.
AM stands for Amplitude Modulation and is the most basic of the types you will encounter using CB radios. The louder the sound that is picked up by a transmitters microphone the more energy is sent out to the radios aerial, this is considered a “messy” form of communication and at high power levels can interfere with TV’s and other radio receivers.
FM or frequency modulation is used in almost all modern equipment from taxi radios to cordless telephones. Its is a much cleaner type of modulation the AM and will cause less interference. As sound is picked up by a transmitter the FM signal increases in frequency, the more sound the more the frequency will shift.
SSB (single sideband operation) is a favorite of radio operators who are trying to work over long distances. The transmitter converts sound into an AM signal then strips away one half of the signal before transmitting it, this gives the radio signal a compressed quality which allows for reception at greater distances. When the signal is received at the other end a device known as a BFO (beat frequency oscillator) recreates the missing half allowing the original sound to be heard.