Observation 4812435: CuPID (99511)

Regarding Observation 4812435

First data frame from CuPID?! It’s alive!?

What’s the likelihood of a successfully decoded frame for a GFSK transmission being a false positive?

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It happens, and that looks like a false positive.

The checksum on AX.25 frames is only a CRC16, and with the amount of random noise we are passing through the decoder we expect to see false positives from time to time. (can’t put a number on it, but it happens)

It’s important to check against the waterfall display to look for signs of the signal that generated the packet. There’s also other factors you can look at, like the expected behaviour of the satellite - would a satellite with the note “only transmits over ground station” really only emit one short packet over an entire observation window?

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Ok, thanks for this. I didn’t realize it was only CRC16 and point taken on a matching pattern that can randonly happen given the volume of bits.

As you noted, there is no visible signal in the waterfall. The frame was decoded about 20 minutes after passing out of the range of the uplink ground station at Boston University-- I was hoping the satellite was experiencing a downlink delay (for whatever reason) and that the decoded frame was an indication the satellite finally made first contact. This appears to not be the case and that of a false positive.

The CuPID team is aware of this observation and is investigating either way.

Thanks again

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