Using GNU Radio for ground station

[rjsdn1120]

Let me briefly explain my GNU Radio setup for the ground station.
I'm testing with the BPSK mode of CubeSatSim.

environment

• RTL-SDR V4
• WSL
• GNU Radio 3.10

GRC Diagram

I am using the BPSK demodulator from gr-satellites

For the "Correlate Access Code - Tag" block, I referred to line 479 of main.c and set the threshold to 5.
For the "Fixed Length to PDU" block, I set the packet length to 500, which is an arbitrary value.
With this setup, I can receive frames. I believe each byte in the output should be interpreted as a bit.

***** VERBOSE PDU DEBUG PRINT ******
()
pdu length =        500 bytes
pdu vector contents =
0000: 00 01 00 01 00 01 00 01 00 01 00 01 00 01 01 00
0010: 00 01 01 00 00 00 01 00 00 00 01 00 00 01 00 01
0020: 01 00 00 00 01 00 01 01 00 00 01 01 00 01 00 01
0030: 01 00 00 00 00 01 01 01 01 00 00 00 01 01 01 01
0040: 01 00 00 00 01 00 01 01 01 00 01 00 01 01 00 01
0050: 00 01 00 00 01 01 01 01 01 00 01 01 00 01 00 01
0060: 01 00 00 00 01 00 00 01 00 01 01 00 01 01 01 00
0070: 01 01 01 01 00 00 00 01 00 01 00 00 00 00 00 01
0080: 00 00 00 01 01 00 01 00 00 00 00 00 01 00 01 00
0090: 00 01 00 01 00 01 01 00 01 00 01 01 01 00 01 00
00a0: 00 01 01 00 01 00 01 00 00 00 01 00 01 01 00 01
00b0: 00 01 00 01 00 01 00 01 00 01 00 01 00 01 00 01
00c0: 00 01 00 01 00 01 00 01 00 01 00 00 00 01 01 01
00d0: 01 00 01 01 00 01 01 01 01 01 00 01 00 01 01 00
00e0: 00 00 00 01 00 01 01 01 00 00 00 01 00 00 00 01
00f0: 00 01 01 01 00 01 01 01 00 01 00 00 01 00 01 00
0100: 01 00 01 00 01 00 00 01 01 00 01 00 01 00 01 00
0110: 00 01 01 00 01 00 01 00 01 00 01 00 00 00 00 01
0120: 01 00 01 01 00 00 00 01 00 01 00 01 00 01 00 01
0130: 01 01 00 01 00 01 00 00 00 01 00 01 01 01 00 01
0140: 00 01 01 01 01 00 01 00 01 01 00 01 00 01 00 01
0150: 00 01 00 01 00 01 00 01 00 01 00 01 00 01 00 01
0160: 00 01 00 01 00 01 00 00 00 01 00 01 00 00 00 00
0170: 01 00 01 01 01 01 00 01 00 00 01 00 01 00 01 00
0180: 00 01 01 01 00 00 00 01 01 00 00 01 00 01 00 01
0190: 01 01 00 00 01 00 01 01 00 01 00 01 00 01 00 01
01a0: 00 01 00 01 00 01 00 01 00 01 00 01 00 01 00 01
01b0: 00 01 00 01 00 01 00 01 00 00 00 01 01 01 01 00
01c0: 00 01 00 01 00 01 00 01 00 01 00 01 01 01 00 01
01d0: 00 00 01 00 00 01 00 01 01 00 01 00 00 01 01 01
01e0: 00 00 01 00 01 01 00 01 00 01 00 01 00 01 00 01
01f0: 00 01 00 01
************************************

Question

• What is the packet length?
• To validate the frame above, can I know the exact parser used?

[Opubose]

Could you share your GRC files with me either now or whenever you're done?

[rjsdn1120]

Github don't support to upload grc file type.
I emailed you!

[alanbjohnston]

This is an interesting project - I'm very interested in it!

The CubeSatSim BPSK Mode 3 emulates the AMSAT Fox-1E CubeSat format. The bit stream is encoded 8b10 which means every 8 bits are transmitted as 10 bits. Here is some SatNOGS code that might be helpful. It says is for FSK (DUV) which is Mode 2, but the bitstream is the same format:

https://gitlab.com/librespacefoundation/satnogs/gr-satnogs/-/blob/master/lib/amsat_duv_decoder.cc

It also mentions Fox-1E which is very similar to our CubeSatSim format with a Sat Id of 99.

You should be able to share snippets of code using Gist: https://gist.github.com instead of uploading it here. Or you could post it in a repository.

Good Luck!

Alan

[rjsdn1120]

Appreciate it!