HORYU-4 CW telemetry format

HORYU-4 is a small satellite from Kyushu Institute of Technology (Japan) designed to test a high voltage solar array in space and observe the effects produced by the charge on the spacecraft due to the high voltage. It transmits telemetry on the 70cm and 13cm amateur bands. It has a CW beacon at 437.375MHz, a 1200baud AFSK telemetry downlink at 437.375MHz and a 100kbaud BPSK telemetry downlink at 2400.3MHz. The digital telemetry downlinks are only active over Japan and use a custom packet format. Here we take a brief look at the format of the CW telemetry.

There is available a CW telemetry format document from Kyushu. Unfortunately, this document is a bit incomplete and the information it contains is not enough to completely decode the CW telemetry. In this post I will give the full details together with a worked example.

The CW beacon from HORYU-4 starts with the callsign "JG6YBW HORYU4", which is followed by 21 hexadecimal digits. These encode the telemetry values. The CW beacon example below was extracted from a recording made on 2n May 2016 which was kindly provided by Yoshimoto JA6PL.

HORYU-4 CW beacon
HORYU-4 CW beacon

The telemetry message in this example is

 FABC11108387B6869801E

The analog telemetry values are encoded as an unsigned 8bit integer, which is read as two consecutive hexadecimal digits (the first digit represents the most significant part). The value of this integer from 0 to 255 is mapped to the telemetry value by means of a "linear scale" that is different for each telemetry channel. The minimum and maximum values of each channel (which correspond to 0 and 255) are not written anywhere in the telemetry format document. However, it is easy to reverse engineer these values using Mike DK3WN's decoder software.

The telemetry values are encoded as follows:

  • Digits 1 and 2. Battery voltage. Value from -393.19mV (00) to 8860.72mV (FF). FA = 8679.27mV.
  • Digits 3 and 4. Battery current. Value from -3710.14mA (00) to 1706.05mA (FF). BC = 282.97mA.
  • Digits 5 and 6. Battery temperature 1. Value from 0ºC (00) to 298.9ºC (FF). 11 = 19.93ºC.
  • Digits 7 and 8. Battery temperature 2. Value from 0ºC (00) to 298.9ºC (FF). 10 = 18.75ºC.
  • Digits 9 and 10. S-band antenna temperature. Value from -150ºC (00) to 148.9ºC (FF). 83 = 3.55ºC.
  • Digits 11 and 12. 1k2 TX temperature. Value from -150ºC (00) to 148.9ºC (FF). 87 = 8.24ºC.
  • Digits 13 and 14. Board temperature. Value from -150ºC (00) to 148.9ºC (FF). B6 = 63.33ºC.
  • Digits 15 and 16. 9k6 TX temperature. Value from -150ºC (00) to 148.9ºC (FF). 86 = 7.07ºC.
  • Digit 17 bit 1. Share memory. 1 = normal, 0 = trouble. In this case, normal.
  • Digit 17 bit 2. Reservation command. 1 = reserve, 0 = nothing. In this case, nothing.
  • Digit 17 bit 3. Operation mode. 1 = mission, 0 = nominal. In this case, nominal.
  • Digit 17 bit 4. Kill switch main. 1 = normal, 0 = kill. In this case, normal.
  • Digit 18 bit 1. Kill switch main. 1 = normal, 0 = kill. In this case, normal.
  • Digit 18 bit 2. Solar cell X. 1 = sunshine, 0 = shadow. In this case, shadow.
  • Digit 18 bit 3. Solar cell +Y. 1 = sunshine, 0 = shadow. In this case, shadow.
  • Digit 18 bit 4. Solar cell -Y. 1 = sunshine, 0 = shadow. In this case, shadow.
  • Digit 19 bit 1. Solar cell +Z. 1 = sunshine, 0 = shadow. In this case, shadow.
  • Digit 19 bit 2. Solar cell -Z. 1 = sunshine, 0 = shadow. In this case, shadow.
  • Digit 19 bit 3. SW_AODS. 1 = onf, 0 = off. In this case, off.
  • Digit 19 bit 4. MUX_OBO. 1 = onf, 0 = off. In this case, off.
  • Digit 20. Hours since restart (as a 4bit unsigned integer). In this case, 1 hour.
  • Digit 21. Operation mode (see values below). E = nominal.

The possible values of the operation mode are:

  • 0. HVSA "Discharge count or I-V measurement".
  • 1. HVSA + OBO "Simple waveform capture + counter" or "Full Waveform Capture + Counter".
  • 3. HVSA + OBO + AVC "Simple Waveform Capture + AVC + Counter" or "Full Waveform Capture + AVC + Counter".
  • 5. HVSA + VAT + OBO "Waveform Capture + Counter".
  • 6. HVSA + VAT + OBO + AVC "Waveform Capture + AVC + Counter".
  • 7. AVC "AVC Reference Picture Mode".
  • 8. DLP, PEC "Normal Measurement".
  • 9. DLP + HVSA, ELF + HVSA, VAT + HVSA "Measurement with High Voltage Source".
  • A. CAM "Timer, Target, Normal Mode".
  • B. SNG.
  • C. S-band downlink.
  • D. S-band processing.
  • E. Nominal.
  • F. Processing satellite.

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