Building a FM Receiver with the USRP and GNU Radio

Overview

In this application note, a Universal Software Radio Peripheral (USRP™) N200/N210 and a WBX daughterboard is used with GNU Radio to build a simple FM receiver. The intent of this example is to:

• Teach some basic DSP and RF concepts including: filtering, demodulation, and sample rate conversion.
• Show how to build graphical applications with GNU Radio Companion
• Illustrate the simplicity of the software tools that can be used with the USRP product family.

Requirements

• USRP with compatible daughterboard to receive 88-108 MHz
• GNU Radio
• UHD

Blocks

UHD Source Block

• Configures USRP
• Receives data stream from USRP

FFT Sink

• Display Fast Fourier Transform of data stream

Low Pass Filter

• Apply low pass filter to data stream
• Optional: Decimation or Interpolation

WBFM Receive

• Demodulates Wide Band Frequency Modulated signal from data stream

Rational Resampler

• Decimate or Interpolate data stream to desired sample rate

Audio Sink

• Audio hardware interface
• Optional: Decimate Audio Rate

Wav File Sink

• Save data stream as WAV file type

WX Widgets

• Textbox - Input field
• Slider - Adjustable slider
• Notebook - Assign Widgets/GUI Sinks to tabs within flowgraph

Variable

• Creates variable within flowgraph

You can download the sample GRC file here: http://files.ettus.com/app_notes/fm_rcvr/fm_example.grc