So, I just downloaded the first file along with a metadata file; I am only going to download the other files after having exhausted this one. After download I have the following files:

In [31]: ls -lh *ATA-X*
-rw-r--r--. 1 alex alex 4.5G May 25 09:31 A_Sign_in_Space-ATA-X.sigmf-data
-rw-r--r--. 1 alex alex  659 May 25 08:47 A_Sign_in_Space-ATA-X.sigmf-meta

OK, now let’s look into the metdata file.

{
    "global": {
        "core:datatype": "ci8",
        "core:description": "A Sign in Space: Allen Telescope Array
recording",
        "core:hw": "ATA 20-antenna beamformer (X polarization)",
        "core:recorder": "blade",
        "core:sample_rate": 1000000,
        "core:sha512":
"fa797c2cd5ea92f4b5ece999182bd62bfb1dcde147dac02a288b10853e9a1e397cb7f70a061ef271c83f96df623d596490957f80c662f81bb593840d8145e42b",
        "core:version": "1.1.0"
    },
    "captures": [
        {
            "core:datetime": "2023-05-24T19:11:17Z",
            "core:frequency": 8410135000,
            "core:sample_start": 0
        }
    ],
    "annotations": []
}

Sooo… what can I derive from this information. It seems to be recording from a x-polarized antenna, recorded at a center frequency of 8410.135 MHz and a sample rate of 1000000 (per second, I assume).

Doing the obvious, using file to check the data format, didn’t yield anything but simply data.

Let’s check the Shannon entropy over the whole file. It is 6.822892707768326, which is not` really helpful. Let’s inspect the file in a hexdump:

In [37]: !hexdump -n 512 -C A_Sign_in_Space-ATA-X.sigmf-data
00000000  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
*
00000040  00 00 00 00 00 00 00 00  00 00 01 01 00 00 04 0a  |................|
00000050  14 04 fe ef cd 2c f9 c5  08 0a e9 16 ff fd da 1c  |.....,..........|
00000060  0f 1b 0c ea 1d 4c 00 f3  f2 d4 0d 19 e7 14 0d eb  |.....L..........|
00000070  e8 01 27 16 2c d8 04 fc  ed 1c 1e 14 08 f6 25 e2  |..'.,.........%.|
00000080  1b 10 e5 06 fb 0d fe eb  cc 09 f8 d8 ea 21 07 01  |.............!..|
00000090  f3 f1 da 0e 1e 00 09 fe  27 17 ee fc ef f8 ea 0b  |........'.......|
000000a0  fa fe 29 05 42 e4 09 1c  0d 0a 06 f0 03 ea d1 09  |..).B...........|
000000b0  05 17 eb 07 f8 18 05 06  f8 f6 2d 06 19 d6 b9 0d  |..........-.....|

Hm, now, there seems to be some kind of empty header of all 0x00 for the first 80 bytes or so, or it’s just a measurement artifact of the receiver having a squelch turned up to some squelch level.

OK, let’s try something else; as the header file indicates that it has a sample rate of 1000000, let’s try to convert this to an audio file and see if there’s something t`o listen to. Let’s grab the first 10 seconds, assume mono audio and a sample rate of 1000000, and throw it at my soundcard.

$ dd if=A_Sign_in_Space-ATA-X.sigmf-data of=10_s.raw bs=1000000 count=10
10+0 records in
10+0 records out
10000000 bytes (10 MB, 9.5 MiB) copied, 0.0126253 s, 792 MB/s

OK, but what kind are the actual samples… 8 bit? 16 bit? Signed? Unsigned? Which endianess? One can only guess, so it’s trial and error.

ffmpeg -f s16le -ar 1000000 -ac 1 -i 10_s.raw s16le_10_s.wav

(note that the resulting file has a length of 5 seconds, as I picked a word-length of 16 bit.)

OK, that just results in white noise. Trying big endian: Also just white noise. Maybe I should fast forward a little, as the first 5 seconds might not be representative at all. Fast forwarding 30 seconds and trying again:

dd if=A_Sign_in_Space-ATA-X.sigmf-data of=1m_10_s.raw bs=1000000 count=10 skip=60
ffmpeg -f s16le -ar 1000000 -ac 1 -i 1m_10_s.raw s16le_1m_10_s.wav

Also: Nope… OK, since I have better things to do now, I’m simply gonna convert the whole file in both flavors - little & big endian - for for the whole 4 GB to be processed and listen to it again.

Read you later…