Introduction to RTL-SDR using MATLAB/Simulink EE423 Applications of Digital Signal Processing Dr. Prust 4/14/2015
RTL-SDR Hardware
RTL-SDR Hardware
Rafael Micro R820T (flexible RF front end)
Realtek RTL2832U (ADC, I/Q Demod, USB data pump)
RTL-SDR Key Specs • Frequency range: 24 MHz – 1766 MHz • Gain Settings: – Automatic Gain Control (AGC) – Manual Gain Settings: 0dB – 49.6dB (29 settings)
• 8-bit I/Q samples (complex baseband) delivered to host PC over USB
RTL-SDR Key Specs • Sample Rates: – Low speed: 225001 to 300000 – High speed: 900001 to 3200000 – Note: Sample rates above 2.4MSPS tend to drop samples
• Output data is complex baseband – Can choose “int16” (raw I/Q samples), or “single”/“double” (normalized to [-1,+1]) types
RTL-SDR in Matlab • “SDRRTLReceiver” system object – Specify radio parameters (e.g., fc, fs, gain) – View parameter settings and status – Receive data % Create receiver and spectrum analyzer System objects hRadio = comm.SDRRTLReceiver( 'CenterFrequency', 91.7e6, ... 'EnableTunerAGC', true, ... 'SampleRate', 1e6, ... 'OutputDataType', 'double');
RTL-SDR in Simulink • RTL-SDR Receiver block
Example “flowgraph” in Simulink
Block Parameters
Block Parameters
“Spectrum Analyzer” Example • Open: sdrrSpectralAnalysisExample
“Play Time” Some items to investigate: – “Tuner gain” setting – Relationship between sampling rate and BW – View some other FM radio stations • Tune to your favorite, OR do a web search to find local stations
Consider the theory: – Baseband spectra are NOT conjugate symmetric, therefore time domain signals must be complex – Carson’s Rule
FM Receiver (Mono) • Open: sdrrFMMonoExample
View Demodulated Waveform • Double-click “FM Receiver” block • In “Simulink Library Browser”, select – DSP System Toolbox – Sinks
• • • •
Drag “Spectrum Analyzer” block to model Connect it to output of “FM Demodulator” Set RTL-SDR block to FM station (e.g. 91.7e6) Run
Back to MATLAB • Download getRawData_RTLSDR.m function [ data, t, infoRTLSDR] = getRawData_RTLSDR( freq, gain, fs, duration ) % function [ data, t, infoRTLSDR] = getRawData_RTLSDR( freq, gain, fs, duration ) % % This function reads complex envelope data from the NooElec R820T SDR % and returns the raw data to the Matlab workspace % % PARAMETERS: % freq is the carrier frequency (in Hz) % gain is the reciever gain (in dB) % fs is the sampling rate (in Hz) % duration is the record time (in seconds) % % RETURN VALUES: % data is the vector of raw data samples % t is the vector of time samples % info is the data structure providing actual RTL-SDR settings for the % recording
Example: >> >> >> >>
[data, t, infoR] = getRawData_RTLSDR(91.7e6,30,240e3,1); plot(t,real(data),’b’) hold on; plot(t,imag(data),’g’)
