• 5G NR downlink reference signals

    Last summer I looked at the demodulation of the 5G NR downlink, using a short recording of an idle srsRAN gNB made by Benjamin Menkuec. In that post I looked at the phase compensation, which is new in NR compared to LTE, the SS/PBCH block, and performed OFDM demodulation of all the signals in the recording. One of these signals was the PDSCH transmitting the SIB1 (which is done periodically even on an idle cell), and its corresponding PDCCH transmission. However, there were some reference signals that I wasn’t able to identify at the time. In this post I will look at these reference signals in detail, and also to the DM-RS (demodulation reference signal) in the PDCCH and PDSCH.

  • Decoding IM-1

    IM-1, the first lunar lander mission from Intuitive Machines, also called Odysseus, was launched on February 15 from KSC, and landed on February 22 near Malapert crater, in the lunar south pole region. The mission has been a partial success. The vehicle did not manage to land upright, and broke one of its legs due to landing with too much horizontal velocity. Despite this unfavourable attitude, communications with the lander have been able to proceed at reduced data rates, and some images and science data have been returned. On February 29, the mission ended, as lunar night started on the landing location. Congratulations to Intuitive Machines for all the milestones achieved in their first mission.

    In this post I will examine some recordings of the S-band telemetry signal done by AMSAT-DL with the 20 metre antenna in Bochum observatory. These recordings were done while the lander was still in-orbit. When landed on the Moon, IM-1 used the same configuration, but the recordings done at Bochum are probably too weak to decode, due to the orientation of the lander antennas.

  • Lunar reflections during SLIM landing

    In my previous post, I looked at the Doppler of the SLIM S-band telemetry signal during its landing on the Moon. I showed some waterfall plots of the signal around the residual carrier. In these, a reflection on the lunar surface was visible. The following figure shows a waterfall of the signal around the residual carrier, after performing Doppler correction and using a PLL to lock to the residual carrier. I was intrigued by the patterns made by these reflections, specially by some bands that look like a ‘1’ shape (the most prominent happens at 14:58).

    In this post I study the geometry of the lunar reflection and find what causes these bands.

  • SLIM lunar landing radiometry

    SLIM, JAXA’s Smart Lander for Investigating Moon, landed near Shioli crater on January 19. Shortly after the landing, the spacecraft was powered down to conserve power, since the probe had landed in an unexpected attitude which shaded its solar panels. After a few days of trying to contact SLIM, JAXA succeeded to reestablish communication with it on January 29. By then the Sun had moved west in the sky at SLIM’s location and had started illuminating the solar panels.

    AMSAT-DL recorded the S-band signal from SLIM during the landing with the 20-meter antenna in Bochum Observatory. In this post I will analyse a recording done between 14:51:51 and 15:21:54 UTC (the touchdown was at 15:20 UTC). I will study the Doppler of the residual carrier and other radiometric quantities rather than the telemetry.

  • Trying to decode LEV-1

    LEV-1 is a small lunar hopper that was carried by the SLIM lunar lander. It was released a few metres above the surface on January 19, as part of the lunar landing of SLIM. LEV-1 transmits telemetry in the 435 MHz amateur satellite band (it has an IARU satellite coordination approval), and also in S-band. Shortly after the landing, CAMRAS received the 437.410 MHz signal from LEV-1 using the 25 m radiotelescope at Dwingeloo. They have published a couple of IQ recordings in their directory of miscellaneous recordings (see the filenames starting by slim_).

    The information about the telemetry signal of LEV-1 is scarce. Its website just says

    Telemetry format of LEV-1 stands on CCSDS. The contents of telemetry are under developing.

    The IARU coordination sheet contains other clues, such as the mention of PCM/PSK/PM, CW, and bitrates of 31, 31.25 and 32 bps, but not much else. Regardless of the mention of CCSDS, I have found that the signal from LEV-1 is quite peculiar. This post is an account of my attempt to decode the data.


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