To Receive EntrySat

The beacon :

Entrysat plans to stay in orbit for at least six months before launching its scientific mission to study the environment of re-entry into the atmosphere. During its orbital mode operation, Entrysat will emit a beacon every minute. This 50-byte message contains basic information such as satellite operating mode, power supply voltages and currents, and platform temperatures (see below). At the approach of the ground station (Toulouse, France) additional information on cubesat sensors will be sent to the ground.

The radio link :

The downlink uses a 9600 bps BPSK modulation on 436.95 MHz frequency on the amateur radio band. Moreover Entrysat has an amateur radio call sign ON2FR essential to transmit on this band. There are several ways to receive and demodulate its signal. This is left to the discretion of everyone to experience the receipt of digital data. However, we propose a solution via an SDR receiver with a RX software (Gqrx from OZ9AEC for example) and a demodulation software like SoundModem from UZ7HO (version G3RUH-BPSK-9K6). The SDR receiver shall be in USB mode, with a bandwidth of at least 24kHz and an offset of the receive frequency of -12kHz to recover the offset of the USB (or + 12kHz if you choose the LSB mode)


Decoding the beacon :

The beacon uses an AX25 frame to deliver a PUS packet to the ECSS standard. Here is an example of a received frame:

8c 6c 96 a8 82 40 e0 : F6KTA-0 (ASCII<<1)
9e 9c 60 64 8c a4 61: ON02FR-0 (ASCII<<1)
03 f0 : Control Bit / Protocol Identifier (fixed)
—————–Information Field ——-
00 00 00 00 : Time not used
————— TM PACKET————–
08 01 : packet ID
c7 29 : packet sequence control
00 12 : packet length
10 : Spare/TM source packet number/ Space (fixed)
03 19 : service / service sub_type (3,25)
23 fe bd cd 17 : time (0x23256^3 + 0xfe256^2 + 0xbd256 + 0xcd + 0x17256^-1) = 2019/02/19 @ 13:14:53
time since 2000/1/1 @ 00:00:00
————–SOURCE DATA——————
06 : SID (6)
00 : Mode Safe
f1 : EPS_VBATT ( 3+0.05×241 = 15.05V ) Battery Voltage
6b : EPS_BATT_VCURRENT ( -1+0.0078740×107 = -157.48mA ) Battery consumption
00 : EPS_3.3V Current (0.025×0 = 0A) 3.3V current sink
00 : EPS_5V Current (0.025×0 = 0A) 5V current sink
9e : TRX_TEMP (-15+0.25×158 = 24.5°C) Radio Transceiver temperature
a0 : EPS_TEMP ( 25 °C) Power Management module temperature
98 : BATT_TEMP ( 23°C ) Battery temperature
1f c6 : Packet CRC
b0 : Frame status, AX.25 transfer frame information field (fixed)
09 be fe 23 : Time, AX.25 transfer frame information field, Coded in Little Endian (last packet sent)

In this example the cubesat is in survival mode. It therefore does not consume current on its 3.3V and 5V power lines payloads (EPS 3.3V and 5V), Current = 0A.
A decoding software has been written by the AMSAT-FR and is available for download. It interfaces with the demodulation software through the KISS server of the latter.

Experience receiving and decoding Entrysat signals !!