Decoding the LilacSat-1 FM to Digital Voice Transponder

LilacSat-1 is an educational CubeSat built by students from the Harbin Institute of Technology (HIT) in China. It was recently launched from the ISS on 25 May 2017 as part of the QB50 science experiment to explore the lower thermosphere, and it is expected to stay in orbit for about 3 months. Apart from BPSK telemetry at 145.935 MHz, LilacSat-1 is interesting because it contains on board an FM to Codec2-BPSK digital voice amateur radio transponder at 145/436 MHz (uplink/downlink). It is probably the first amateur radio satellite to contain an FM to digital voice transponder.

To decode LilacSat-1 digital voice and telemetry you can use a Linux live CD provided by HIT, or download the GNU Radio decoder directly from the LilacSat-1 information page on the HIT website. The GNU Radio program can be used with any GNU Radio compatible SDR, such as an RTL-SDR.

Over on his blog, destevez has also created a lower latency digital voice decoder for LilacSat-1 that can found in the gr-satellites GNU Radio package, which contains decoders for multiple satellites as well. Destevez has also written about the Codec2 implementation used in LilacSat-1 in one of his previous posts.

An example of LilacSat-1 being decoded has also been uploaded by YouTube by Scott Chapman. In his test he used an RTL-SDR to work the pass live, but in the video shows an offline decoding received by his SDRplay which was also monitoring the same pass.

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