FM (Frequency Modulation) encodes information into the carrier frequency. FM transmissions therefore center around a carrier frequency, and the frequency slightly changes based on the information encoded.
Today, FM is widely used in public broadcast, telecommunications, voice radios, and signal processing.
Analog signals can be directly modulated onto the carrier frequency by feeding the message into a voltage-controlled oscillator.
Digital Data Transmission
For digital transmissions, FSK (Frequency-shift keying) is typically used: a set of frequency deviations are used to define symbols. In its most basic form, just two frequency deviations exist, representing the bits 1 and 0.
Other more sophisticated encoding schemes exist. LoRa, for example, is a digital long range transmission protocol based on FM that can travel long distances while using very low radio emissions. It is based on Chirp-Spread-Spectrum (CSS):
- Chirp: A chirp is a radio signal with a dynamically increasing or decreasing frequency, adding additional information content.
- Spread Spectrum: The narrow bandwith of the carrier signal is spread out to a much wider frequency spectrum. This makes it more resilient towards noise signals and almost impossible to tap and listening in by unwanted third party. This modulation method is also used in WiFi, Bluetooth, and ZigBee.
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(content created Apr 15, 2024)