PlutoSDR FM Voice Transmission System: From Audio File to Wireless Reception
A complete guide to building an FM voice transmission system using PlutoSDR — covering UI design, transmitter/receiver configuration, FM modulation/demodulation, audio playback, and signal analysis.
Introduction to FM Modulation
FM (Frequency Modulation) is an analog modulation technique where the baseband signal is carried by variations in the carrier frequency. It is an angle modulation method and is inherently non‑linear. FM modulation and demodulation principles are well‑documented and widely available — this article focuses on system implementation rather than theoretical fundamentals.
System Overview & UI Design
The system implements FM signal transmission and reception using PlutoSDR. A custom UI interface provides:
- Voice file selection: Dropdown menu for selecting the audio file to transmit (analog signal)
- Receiver gain control
- Carrier frequency configuration
- Received audio saving: Save demodulated audio for later analysis and playback
System Configuration Parameters
The following MATLAB code configures the PlutoSDR transmitter and receiver. Parameters use a combination of UI‑driven dynamic configuration and static settings.
% Pluto transmitter configuration
sdrTransmitter = sdrtx(deviceNameSDR);
sdrTransmitter.RadioID = 'usb:0';
sdrTransmitter.BasebandSampleRate = fs; % Sampling frequency
sdrTransmitter.CenterFrequency = sim_options.carr_f * 1e9; % Carrier frequency
sdrTransmitter.ShowAdvancedProperties = true;
sdrTransmitter.Gain = 0;
% Pluto receiver configuration
sdrReceiver = sdrrx(deviceNameSDR);
sdrReceiver.RadioID = 'usb:0';
sdrReceiver.BasebandSampleRate = fs; % Sampling frequency
sdrReceiver.CenterFrequency = sim_options.carr_f * 1e9; % Carrier frequency
sdrReceiver.Gain = 30; % Receiver gainTransmission Workflow
- Load the selected voice file
- Play the original audio (listen to the transmitted signal)
- Pass the signal through the FM modulator
- Transmit via the PlutoSDR antenna
Reception Workflow
- Signal propagates through the wireless channel
- Receiving antenna captures the signal
- Pass the received signal through the FM demodulator
- Play back the demodulated audio for comparison with the original
- Save the received audio using the filename specified in the UI
Audio Comparison Results
The system displays a comparison between transmitted and received audio signals:
The system also displays time‑domain and frequency‑domain comparisons between transmitted and received signals:
Key Takeaways
- FM modulation provides robust analog voice transmission over wireless channels
- The PlutoSDR platform successfully implements both transmission and reception with simple MATLAB configurations
- Received audio can be saved for offline analysis and playback
- Time and frequency domain comparisons help visualize channel effects on the signal
Project Files & Resources
The complete project files, including MATLAB code, UI design, and documentation, are available upon request.
Hardware Support
This system is designed for the PlutoSDR platform. For a ready‑to‑use PlutoSDR with full frequency support (70MHz–6GHz) and Gigabit Ethernet: