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How to Measure and Decode an ISM868 Car Key

We are using the following mission to capture and record the car key:

ISM868 Car Key Capturing Mission

After capuring the transmission we get the following 2D and 3D waterfall view. We can see 4 quite narrow transmissions:

ISM868 Car Key RF Capture

If we look nearer at one of the 4 transmissions we can notice that it is frequency shifted:

ISM868 GFSK Modulation Spectrum

If we zoom into the bottom part of the transmisson the modulation and coding gets much clearer:

ISM868 Car Key Decoding @ 868MHz

This looks like a GFSK coding. We can now decode the transmission with the help of our IQ Pulse Inspector block and a new mission:

IQ Pulse Inspector Block Mission

After a new recoding we get the follwing 4 automatic decodings:

  • GMSK
  • GFSK
  • GFSK
  • GFSK

Automatic ISM868 Car Key Decoding

We can now click at one of the decoded transmissions and get a full bit wise decoding:

Bit Wise GFSK Car Key Decoding

If you are interested how the IQ data get decoded simply zoom in to the graph. You can now see I and Q and how the decoding took place:

ISM868 IQ GFSK Decoding

Now it will be interesting to save the IQ data on disk and to play them back via the SPECTRAN V6 inbuild IQ vector signal generator. Will the car unlock? But this is an other story.