Low Pass Filter Example

This tutorial will describe how to use a low-pass filter in GNU Radio. The previous tutorial can be found here: Creating Your First Block

Creating the Flowgraph

Begin by adding the following blocks to the GRC work space:

1. Signal Source
2. Low Pass Filter
3. Throttle
4. QT GUI Frequency Sink
5. QT GUI Range

Connect the blocks in the following manner:

The QT GUI Range block will be used to control the frequency of the Signal Source block. Double-click the QT GUI Range block and edit the properties:

• Id: frequency
• Default Value: 0
• Start: -samp_rate/2
• Stop: samp_rate/2

Click OK to save.

Double-click the Signal Source block and enter frequency from the QT GUI Range variable:

Click OK to save. The flowgraph will look like the following image. Notice that the Low Pass Filter has a Cutoff Freq and Transition Width of 0:

Double-click the Low Pass Filter block and edit the properties:

• Cutoff freq: samp_rate/4
• Transition Width: samp_rate/8