Receiving SSTV images from SONATE-2
#RadioIn March 2024, the Julius Maximilian University of Würzburg launched a CubeSat called SONATE-2 (SOlutus NAno satelliTE 2) with a ham radio payload. The mission includes transmitting images via analog SSTV on several occasions. Information about the downlink frequency and modulation, as well as the transmission schedule, can be found on the projects page with information for radio amateurs.
This satellite did a pass over my location which coincided with the SSTV transmission scheduled for 20.05.2024 13:52:00 UTC. I made two simultaneous recordings of the signal. The first setup consisted of a V-dipole antenna built from the RTL-SDR blog dipole antenna kit connected to an RTL-SDR and my phone running SDR++ and the second setup used a QFH antenna built for NOAA-APT signals connected to an AirSpy mini and my laptop.
Both setups used narrowband FM centered at 145.88 MHz with a bandwidth of 12.5 kHz. While the signal was clearly visible in the waterfall, the images resulting from both recordings were suboptimal. The image created from the recording made with the V-dipole antenna is rather noisy. Furthermore, QSSTV messed up the synchronization for the recording taken with the QFH antenna, resulting in a distorted image.
After a bit of fiddling in Audacity - which was mostly trial and error - I was able to align both recordings and combine them into a single sound file using the better parts of each.
Finally, the resulting image is considerably less noisy. The beginning of the transmission is still missing, but in the top left corner a yellow box with the satellite’s call sign, DP0SNX, is faintly visible.
The image was captured by the satellite’s wide-angle color camera and shows the Strait of Gibraltar. This was not a live image. Instead, it appears to be the first high-resolution image captured by the satellite several weeks before.