We're making an open-source $30 GPS/mesh radio, would like advice

Re:We're making an open-source $30 GPS/mesh radio, would lik... by bigiain on Tuesday March 10, 2020 @07:38PM (#22541236)

This stack overflow question has some nice pictures of the LoRa "chirps". They use rising/falling frequency modulation to allow operation at startlingly low signal to noise ratios.

(Also, the hardware they're using is fairly generic, and pretty much all the vendors selling them offer them in 915/920MHz and also 868MHz and 433MHz variants. I've seen claims of over 10km range with 433MHz LoRa gear without special antennas or clear line-of-sight...)

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Re:We're making an open-source $30 GPS/mesh radio, would lik... by bigiain on Tuesday March 10, 2020 @10:57PM (#22542532)

Just noticed I'd left out the link to the SO question I mentioned (and it's too long ago to let me edit that post):

https://electronics.stackexchange.com/questions/278192/under...

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Re:We're making an open-source $30 GPS/mesh radio, would lik... by dfox on Tuesday March 10, 2020 @08:45PM (#22541746)

LoRa has very peculiar modulation scheme that in the end is not CDMA-ish spread spectrum but an interesting way how to extend straight FSK into spread spectrum modulation with respectable processing gain and interference rejection.

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Re:We're making an open-source $30 GPS/mesh radio, would lik... by bigiain on Tuesday March 10, 2020 @10:55PM (#22542520)

I recall reading that part of the design was so that not only was it good at rejecting interference, but that it also caused little interference to other users of the spectrum.

If someone else's ISM radio is using a specific frequency (perhaps with CDMA or TDMA), a "chirp" that's spears over about a hundred kHz and -20db or so down in the noise is unlikely to bother them, but is quite useable/reliable for the LORA gear to detect.

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