Low Pass Filter Example

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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:

LPFTutorialFlowgraphStart.png

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

SetQTGUIRangeValuesFrequency.png

Click OK to save.

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

EditSignalSourceFrequency.png

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:

FlowgraphWithZeroCutoffFrequency.png

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