GNU Radio “hello world” SDR Project

For people interested in using GNU Radio for real radio DSP projects a great place to start is to pair the GNU Radio DSP with the inexpensive RTL-SDR VHF/UHF receiver.  The DSP can be customized to fit the intended use.  For example, the GNU Radio DSP can configure the RTL-SDR to receive AM from commercial aircraft traffic, WBFM Broadcast stations, NBFM repeaters in the amateur radio bands, not to mention CW and SSB modulation etc.

This GNU Radio flow graph is configured as an FM Broadcast radio receiver.  Review of the flow graph, from left to right, depicts the complex digital signal stream from the RTL-SDR receiver Source, to the IF Low Pass filter, followed by the WBFM Receive demodulator block.  At this point in the data stream, the output is converted from a complex (I & Q) data stream to floating point (I only) data stream that is compatible with the computer sound card.  The data stream continues through an audio Low-Pass Filter, a Multiply Constant block (which functions as an audio volume control), finally to and Audio Sink block.  The Audio Sink block is the computer sound card.  The D/A converter in the sound card converts the digital data stream back to an analog signal that can be heard in the computer speakers.  The second row of DSP blocks in the flowgraph depicts the DSP blocks necessary to display a WX GUI FFT Sink or panadapter display.  The DSP block parameters are displayed in each block.

RTL-SDR FM Broadcast Receiver GNU Radio Flowgraph

When the flowgraph is executed the Operating GUI appears on the screen.  Inspection of the Operating GUI shows the RF FFT panadapter display in the center of the screen.  Observe the spectrum of an FM broadcast station.  The primary composite audio signal is displayed in the center of the display with the signal data subcarriers above and below in frequency.  Below the FFT displays are WX Slider controls for Frequency Tuning, Audio Gain control, and a WX GUI Chooser for Station Choice of the RTL-SDR.

RTL-SDR FM Broadcast Receiver Operating GUI showing a commercial FM Broadcast signal

Read the instructions regarding the RTL-SDR driver fix for the Ubuntu OS: Correct the RTL SDR USB connection problem

The .grc file for this receiver: RTL-SDR FM Broadcast Receiver.grc can be downloaded and executed in your own GNU Radio application.  Read important introductory information here regarding the downloading procedure: How to download and save .grc files.  When the flow .grc file is executed with the RTL-SDR connected to an antenna, the RTL-SDR will receive local FM Broadcast stations.