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FM Broadcast Receiver in Simulink

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This example shows how to build an FM mono or stereo receiver. You can either use previously captured signals, or receive signals in real time using the RTL-SDR, ADALM-PLUTO or USRP™ radio.

Required Hardware and Software

By default, this example runs using previously captured data. Optionally, you can receive signals over-the-air. For this, you also need one of the following:

Introduction

For an introduction to the FM broadcasting technology and demodulation of these signals, refer to the FM Broadcast Receiver example.

Running the Example

To run the example using captured signals, select the FM Broadcast Captured Signal block as the source using the Signal Source Selector block. Then click the run button.

To run the example using the RTL-SDR radio, ADALM-PLUTO radio or USRP radio as the source, select the corresponding RTL-SDR Receiver, ADALM-PLUTO Radio Receiver or USRP Radio Receiver block as the source using the Signal Source Selector block. Double-click the Center Frequency (MHz) block and select the value to the center frequency to a broadcast FM radio station near you.

If you hear some dropouts or delay in the sound, run the model in Accelerator mode. From the model menu, select Simulation->Accelerator, then click the run button. If you still experience dropouts or delay in Accelerator mode, try running the model in Rapid Accelerator mode.

Receiver Structure

The receiver structure in this block diagram represents the FMReceiverSimulinkExample.slx model used in this example. The processing has three main parts: signal source, FM broadcast demodulation, and audio output.

Signal Source

This example can use three signal sources:

  1. ''Captured Signal'': Over-the-air signals written to a file and sourced using a Baseband File Reader block at 228e3 samples per second.

  2. ''RTL-SDR Radio'': RTL-SDR radio running at 200e3 samples per second. Set the center frequency to a broadcast FM radio station near you.

  3. ''ADALM-PLUTO Radio Receiver'': ADALM-PLUTO radio running at 200e3 samples per second. Set the center frequency to a broadcast FM radio station near you.

  4. ''USRP Radio Receiver'': USRP radio running at 200e3 samples per second. Set the center frequency to a broadcast FM radio station near you.

FM Broadcast Demodulation

The baseband samples received from the signal source are processed by the FM Broadcast Demodulation Baseband block. This block converts the input sampling rate of 228 kHz to 45.6 kHz, the sampling rate for your host computer's audio device. According to the FM broadcast standard in the United States, the de-emphasis lowpass filter time constant is set to 75 microseconds. This example processes received mono signals. The demodulator can also process stereo signals.

To perform stereo decoding, the FM Broadcast Demodulator Baseband object uses a peaking filter which picks out the 19 kHz pilot tone from which the 38 kHz carrier is created. Using the resulting carrier signal, the FM Broadcast Demodulator Baseband block downconverts the L-R signal, centered at 38 kHz, to baseband. Afterwards, the L-R and L+R signals pass through a 75 microsecond de-emphasis filter. The FM Broadcast Demodulator Baseband block separates the L and R signals and converts them to the 45.6 kHz audio signal.

Audio Device Writer

Play the demodulated audio signals through your computer's speakers using the Audio Device Writer block.

Further Exploration

To further explore the example, you can vary the center frequency of the RTL-SDR radio, ADALM-PLUTO radio or USRP radio and listen to other radio stations using the Center Frequency (MHz) block.

You can set the Stereo property of the FM Broadcast Demodulator Baseband block to true to process the signals in stereo fashion and compare the sound quality.

Selected Bibliography

https://en.wikipedia.org/wiki/FM_broadcasting