CubeSat ENSO on GNURadio – Telecommunications, Navigation & Electronics

Introduction

This past summer I was able to successfully receive Cubesats EIRSAT-1 and Veronika (Ref.1/6). Both Cubesats have since decayed from orbit according to the SatNOGS database. Looking through the gr_satellites supported Cubesats, I noticed that ENSO was operational having been launched recently in 2023. ENSO or ROBUSTA-1E is a 1U Cubesat developed by the Université de Montpellier in France (Ref.7). According to the SatNOGS data base ENSO transmits on 436.500MHz GMSK/9600baud.

Reception Parameters

Fig.1 Equipment & Software Setup CubeSat Reception

Fig.2 GNURadio gr_satellites Schematic Decoding CubeSat ENSO

Figure 1 shows the equipment setup. The UHF Yagi is pointed due East. The 433MHz BPF/LNA/RTL-SDR is connected to the Yagi with a sma to catv adapter. A long usb cable then feeds a laptop indoors. SDR# is used and the sampling rate is set at 250Ksps to keep file size down. The frequency is set 20KHz below the satellite frequency. The reason for this is to allow for Doppler shift. On playback, you can measure the actual packet receive frequency then set this in the GNURadio Frequency Translation Filter. The Baseband IQ recorder is used and I start recording the minute my QTH appears in the satellite footprint. The satellite pass is typically about 5-8 minutes so the files get big. You can trim them later in Audacity. I keep the gain low at 19.7dB, but this depends on the active QRM, so I adjust this for minimum intermod. Figure 2 shows the GNURadio schematic used with gr_satellites Satellite Decoder set for “ENSO”.

Signal Capture Nov1st_2025

Fig.4 GNURC Decode for ENSO Nov1st_2025 Freq Shift = 15.5KHz

Figure 3 shows a close pass of ENSO at Elev=55deg on Nov1st and Figure 4 shows the GNURadio decode. The SDR# center frequency was 436.480MHz and the freq shift was 15.5KHz. The WAV file repeats and the decoder gave several decodes and finally settled on 15bytes.

Signal Capture Nov3rd_2025

Fig.6 GNURC Decode for ENSO Nov3rd_2025 Freq Shift = 9KHz

Figure 5 shows a close pass of ENSO at Elev=38deg on Nov3rd and Figure 6 shows the GNURadio decode. The SDR# center frequency was 436.500MHz and the freq shift was 9KHz.