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But what *is* the spreading factor?

LoRa Basics™
#1

I’m a student trying to write a term paper about a project that uses LoRa. After looking for information on what the spreading factor is, I’ve found three explanations and I’m completely lost on which one to use for my paper…

1: Number of bits encoded by one symbol.
2: Speed of a chirp/chirp frequency
3: SF = Chipping factor, number of chips sent per bit

Can someone help me on this? Sources would be very appreciated!

#2

This video might be interesting https://www.youtube.com/watch?v=dxYY097QNs0

#3

I was planning on adding the relevant sources, but couldn’t due to the limit of 2 links. This is the source for theory 2. After some more digging I found this paper which claims 1 and 2 to be correct (see 2.1 LoRa modulation). Source for theory two is the datasheet of the chip my HW uses (see 6.1.1.1 Spreading Factor). Latter doesn’t make much sense to me though…