Technology
Frequency Modulation
Quick fact
FM radio was invented by Edwin Armstrong in 1933 and was initially met with resistance from the radio industry, which was heavily invested in AM technology.
Why this is interesting
You've likely noticed that FM radio sounds clearer than AM, even in areas with interference—why does changing frequency instead of amplitude make such a difference?
Read the full explanation
Understanding Frequency Modulation
Imagine a steady, pure tone (the carrier wave) like a constant whistle. To send a message—say, a melody—you could change the loudness of the whistle (amplitude modulation), but static and noise distort loudness easily. Instead, frequency modulation keeps the whistle at the same volume but subtly changes its pitch in sync with the melody. The receiver detects those pitch variations and reconstructs the original sound. This method is far more resistant to electrical interference because noise typically affects amplitude, not frequency.
A deeper explanation
In frequency modulation, the instantaneous frequency of the carrier signal deviates from its center frequency by an amount proportional to the instantaneous amplitude of the modulating signal. The maximum deviation is constant for a given system and determines the bandwidth. Because the carrier's amplitude remains constant, amplitude-based noise (like static) has minimal effect. This noise immunity, along with the ability to trade bandwidth for signal-to-noise ratio (via pre-emphasis and de-emphasis), makes FM ideal for high-fidelity broadcasting. The modulation index (ratio of deviation to modulating frequency) governs the spectral spread, producing an infinite but practically limited set of sidebands. FM's robustness is why it's used for music radio, analog television sound, and many two-way radio systems.