Software Defined Radio with HackRF, Lesson 8 - Great Scott Gadgets

Great Scott Gadgets

Software Defined Radio with HackRF, Lesson 8

On-Off Keying

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

  • analyzing a garage door opener remote
  • On-Off Keying (OOK)
  • rolling codes
  • fixed codes


  1. Find a garage door opener remote control or similar device. Does it have an FCC ID?

  2. If it has an FCC ID, look it up. What is the device’s operating frequency?

  3. Use GNU Radio Companion to find the signal produced by the device. You will probably need to hold down the button to make it transmit continuously. At what frequency did you find the device? (Hint: If your device does not have an FCC ID, try frequencies from 300 MHz to 433 MHz.)

  4. Look at the FFT plot of the signal. Does it appear to have very narrow bandwidth like my remote, or does it span more than a few kHz?

  5. Use a scope plot to look at the signal. Adjust the time scale and amplitude scale so that you can see complete data packets. Does it look like On-Off Keying (OOK)?

  6. If you are able to visually decode the transmitted bits, does the same sequence of bits repeat while you hold down the button? Does the sequence change if you release the button and press it again?



  • 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.