User:Duggabe

DRAFT 3rd REVISION Guided_Tutorial_Hardware_Considerations

Introduction

One of the more basic (and also incredibly useful) things you can do in GNU Radio with a receiver is to create a software radio spectrum analyzer. This is also a great first step because it will verify that your hardware is working correctly.

Prerequisites

• Tutorials:
  • A brief introduction to GNU Radio, SDR, and DSP
  • Intro to GR usage: GRC and flowgraphs
  • Understanding sample rate

What Will I Need?

There is a large and growing number of vendors who provide hardware with GNU Radio drivers.They span from very cheap ($20) receivers to very high-performance tens-of-thousands-of-dollars systems. Parameters for four of the most popular devices are presented below. Other devices are listed in Hardware.

Creating a Software Radio Spectrum Analyzer

This example uses an Ettus Research USRP B200 and the USRP Hardware Driver (UHD). The B200 provides a fully integrated platform with continuous frequency coverage from 70 MHz to 6 GHz.

In order to use UHD blocks, you must have UHD installed. See Installing the USRP.

Using gnuradio-companion (GRC) and the following Block descriptions, build this flowgraph.

Setting Parameters

The parameters are set as shown:

    

Tuning and Using the Spectrum Analyzer

Set the following parameters in the QT GUI Sink block:

• Center Frequency (Hz): tuning
• Bandwidth (Hz): samp_rate
• Show RF Freq: Yes

The analyzer can be tuned with the Frequency control widget. If you check the "Display RF Frequencies" box in the run-time GUI window, then the scale on the 'Frequency Display' and 'Waterfall Display' tabs will show the actual frequencies with the tuned frequency in the center.

You can adjust the Sample Rate to see the effects on the received spectrum. This trace shows four FM stations.

Hardware Considerations

Setting the sample rate involves several factors to consider.

• The various hardware devices have limits on what sample rates they can deliver. Some, such as the FunCube Pro+, have a fixed sample rate of 192kHz. Setting the flowgraph sample rate must be within the limitations of the device.
• The computer hardware and operating system you are using will set limitations on the data throughput, such as:
  • USB2 vs USB3
  • processor speed
  • number of CPU cores
• Data overruns are indicated by the letter 'O' displayed on the terminal screen. These are because the input data stream is producing data faster than the flowgraph can consume it. Adjusting the sample rate and/or the input buffer size (where available) should alleviate the problem.

Building an FM Receiver

Now that you have a tested input device, you can build an FM Receiver with it. See the following examples and use your hardware.

• Wide Band FM Receive Block
• Narrow Band FM Receive Block
• RTL-SDR FM Receiver

For audio considerations, see Audio_Sink.