What is AM Modulation?
AM (Amplitude Modulation,) originated in the mid 1870’s and is the simplest form of radio broadcast. Its ‘carrier wave’ is modulated in amplitude while the frequency remains the same- this means that a signal can remain steady over a longer distance. The receiver detects changes in the amplitude of the carrier frequency and amplifies it to drive a speaker.
Unfortunately, AM broadcasting is susceptible to distortion and harbours background noise making the sound quality poorer overall. So why use AM? In addition to its signal remaining steady over large distances, it was, until recently, the cheaper option for broadcasting given its simplicity to implement. It is still used for radio stations globally, as well as walkie talkies which do not necessarily require crystal clear sound.
What is FM Modulation?
FM (Frequency Modulation,) was developed in 1933 and provides some substantial benefits over AM. It is able to send out two channels of information simultaneously and due to its complex algorithms, is able to produce stereo sound by utilising both the left and right audio channels. The sound quality is far superior to that of AM radio because the signal does not degrade as easily and the environmental factors which disrupt AM signals do not affect frequency.
While this sounds ideal for communication, the distance FM signals are able to reach is nowhere near that of AM and drop out at around 50 miles from the station. Due to its complexity and the need for a higher power output, FM broadcasting was initially a much more expensive option but this has changed over the years and is now on a par with AM, meaning even smaller radio stations are able to broadcast with much better clarity.
In addition to radio broadcasting, FM is utilised by electronic music technology such as wireless microphones and electric guitars. This is the natural choice over AM given the quality of sound it provides.
In summary, AM provides a steady and reliable signal over long distances, although the sound quality is not the best. FM can create a much better quality of sound but only works over shorter areas. Given the advancement in technology it is now common to find circuitry for both modulations within a single device.