Software Defined Radio with HackRF, Lesson 2 - Great Scott Gadgets

Great Scott Gadgets

Software Defined Radio with HackRF, Lesson 2


In order to clearly see my screen during the demonstration, viewing the video in full screen mode may help. Even better: You can download this video in high resolution (720p). (torrent)

In this Lesson

  • lesson 1 homework review
  • introduction to Digital Signal Processing
  • a simple flowgraph


  1. Create a flowgraph like the one in the video or the screenshot below.
    simple flowgraph screenshot

  2. Does the flowgraph behave differently if you remove the throttle block? (Connect the source directly to the sink.)

  3. Does the FFT sink correctly indicate the frequency produced by the source? What if the source and sink have different sample rates configured?

  4. What happens if you configure the signal source with various frequencies between 0 and 16k?

  5. What if you specify frequencies greater than 16k? Any idea why?

  6. What if you specify negative frequencies? Mathematically, is there a difference between cos(x) and cos(-x)?

  7. Does the plot indicate the presence of any frequencies other than the one produced by the source? (Hint: Use Autoscale or increase dB/Div.) What is the apparent amplitude of the noise? Why is there any noise at all?

  8. Try multiple signal sources added together. Are there any other interesting operations you could try?

  9. Try various waveforms (instead of cosine) in the signal source.



  • 5 October 2015: I used the WX GUI option in GNU Radio Companion. The default has since changed from WX GUI to QT GUI in the Options block. If you are using a newer version of GNU Radio, you’ll need to change it back to WX GUI to follow along with my flowgraph.

Software Defined Radio with HackRF is copyright 2014, 2015 by Michael Ossmann and is released under the CC BY license.