Spectrum Analysis of Signals
This example shows downstream spectrum analysis of signals using MATLAB®, Communications Toolbox™ and DSP System Toolbox™. You can either use captured signals, or receive signals in real time using the RTL-SDR Radio, ADALM-PLUTO Radio or USRP™ Radio. You can change the radio's center frequency to tune the radio to a band where a signal is present. You can then use the spectrum analyzer to view and make measurements on the received spectrum.
Required Hardware and Software
To run this example using captured signals, you need the following software:
To receive signals in real time, you also need one of the following hardware:
RTL-SDR radio and the corresponding software Communications Toolbox Support Package for RTL-SDR Radio
ADALM-PLUTO radio and the corresponding software Communications Toolbox Support Package for ADALM-PLUTO Radio
USRP radio and the corresponding software Communications Toolbox Support Package for USRP Radio
For a full list of Communications Toolbox supported SDR platforms, refer to the "MATLAB and Simulink Hardware Support for SDR" section of Software-Defined Radio (SDR).
The receiver asks for user input and initializes variables. Then, it calls the signal source and FM broadcast receiver in a loop. The loop also keeps track of the radio time using the frame duration and lost samples reported by the signal source.
For the option to change default settings, set |cmdlineInput| to 1.
cmdlineInput = false; if cmdlineInput % Request user input from the command-line for application parameters userInput = helperSpectralAnalysisUserInput; % Set initial parameters [SAParams, sigSrc] = helperSpectralAnalysisConfig(userInput); else % Set initial parameters load defaultInputSpecAnalysis.mat [SAParams, sigSrc] = helperSpectralAnalysisConfig; end
spectrumAnalyzer object and configure based on user input
hSpectrum = spectrumAnalyzer(... 'Name', 'Passband Spectrum',... 'Title', 'Passband Spectrum', ... 'Method', 'Welch', ... 'SpectrumType', 'Power density', ... 'FrequencySpan', 'Full', ... 'SampleRate', SAParams.FrontEndSampleRate, ... 'SpectralAverages', 50, ... 'FrequencyOffset', SAParams.CenterFrequency, ... 'YLimits', [-120 10], ... 'YLabel', 'Magnitude-squared, dB', ... 'Position', figposition([50 30 30 40]));
View the spectrum. While the spectrum analyzer is running, you can measure peaks, occupied bandwidth, and other properties of the signal.
% Initialize radio time radioTime = 0; % Main loop while radioTime < userInput.Duration % Receive baseband samples (Signal Source) if SAParams.isSourceRadio if SAParams.isSourcePlutoSDR rcv = sigSrc(); lost = 0; late = 1; elseif SAParams.isSourceUsrpRadio rcv= sigSrc(); lost = 0; else [rcv,~,lost,late] = sigSrc(); end else rcv = sigSrc(); lost = 0; late = 1; end rcv = rcv - mean(rcv); % Remove DC component. step(hSpectrum, rcv); % Update radio time. If there were lost samples, add those too. radioTime = radioTime + SAParams.FrontEndFrameTime + ... double(lost)/SAParams.FrontEndSampleRate; end % Release all System objects release(sigSrc); release(hSpectrum);
In this example, you used Communications Toolbox™ System objects to analyze the spectrum of a received signal.