How to Demodulate FM Signals Over-the-Air

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Extracting audio from OTA FM signals

Demodulating frequency-modulated (FM) signals requires extracting the original information, typically of an audio signal, from the carrier frequency. As the FM signal frequency deviates from its carrier, the output voltage of the demodulator changes. This voltage represents the instantaneous frequency of the FM signal and corresponds to the audio signal. Engineers demodulate FM signals by optimizing their spectrum analyzer settings — activating the preamplifier, minimizing RF input attenuation, and fine-tuning the reference level to enhance signal clarity and reduce audio static. For testing compliance with standards such as the International Telecommunication Union (ITU), test against maximum FM deviation and analyze carrier power, frequency, and modulation rate.

Extracting audio from the FM signal over-the-air requires a frequency demodulator to convert the FM signal from the radio transmitter into its baseband audio signal. Understanding the core requirements of engineers for FM demodulation lays the groundwork for selecting the right tools and methods. Engineers need spectrum analyzers with wide dynamic range and accurate frequency readings to electronically monitor radio signals and other wireless transmissions. When assessing real-world wireless device performance, handheld spectrum analyzers are preferable to benchtop alternatives due to their portability and over-the-air testing capabilities. Handheld analyzers offer features such as filtering, data display and logging, and audio output, allowing operators to perform tasks such as analog demodulation during spectrum analysis.

Demodulate FM Signals Over-the-Air with FieldFox Handheld Analyzer analog demodulation

FM signal over-the-air demodulation solution

Demodulating radio-transmitted FM signals over-the-air requires a spectrum analyzer. The Keysight FieldFox handheld analyzer performs scanning, demodulation, filtering, audio output, and data display with a single portable instrument. Collect and analyze real-time information such as carrier power, frequency, modulation rate, and deviation. Conduct ITU conformance testing of FM deviation by selecting radio standards and deviation types. Tune to a signal and listen to the audio tones with the built-in tune and listen capabilities.

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