[1] https://github.com/kc1awv/KISSLoRaTNC

APRS aside, as far as I've found, there are about a half dozen Winlink nodes in the area and one BBS. And one lovely node in Cambridge (KZ2X-1 [1]) which provides connectivity to a bevy of ancient (though virtualized) OSes.

I don't know how much AMPRnet activity there is. There are only 7 allocations in the area (mine included). I'd love to be able to e.g. log in to my home network from a few radio hops away but I don't think there's any infrastructure in place for that (such as Mobile IP).

[1] https://kz2x.radio/posts/complex/

Is your goal nondetection? If so, know that triangulating a radio signal is fairly straightforward, even in a dragnet fashion. The exception I think is something like cryptographic DSSS (found in military use) wherein not only is the signal far below the noise floor, but the spreading function is not predictable by an adversary (LoRa being very much predictable). Even then, you're limited by physics to only be able to transmit so far without the signal being detectable near the transmitter.

The trick is understanding LoRa's trick, which is simply to "skew" the signal across time (via chirps), modulo a window of the configured bandwidth around the center frequency. The key is that the skew rate is purely a function of the spreading factor, bandwidth, and IQ polarity (= pol × BW² / 2^SF), so there's a small-ish finite number of skew rates. So you can just modulate raw IQ data with carriers at each of these skew rates to find one which gives you a bunch of carrier waves that hop around discretely at about twice the symbol rate, looking like an FSK signal. You can then bin this at a factor of, say 2^(SF-2) to correlate the signal and raise it up above the noise floor, on which you can apply any standard triangulation technique.

I'll try vetting this soon and reply to this post with results.

(500 kHz bandwidth is indeed a valid setting for the underlying LoRa protocol, and is used when the radios get certified.)

Unfortunately the community meshes in most/all US metros have coalesced around these settings, meaning one is forced to choose between linking with "the" mesh, or operating legally.

[1] https://www.ecfr.gov/current/title-47/part-15/section-15.247...

Comments URL: https://news.ycombinator.com/item?id=46252266

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With the "cell phone + companion radio" setup which is currently very popular, it would seem the correct solution is to perform encryption on the phone – using the Signal protocol – and use the companion radio only to send/receive these blobs.

This has the added benefit that you can pair with _any_ arbitrary companion radio, rather than your identity being tied to one specific radio you own.

For triangulation though, if you have a reference signal at a known location, TDoA (time difference of arrival) requires less hardware (just a single receiver at each location, e.g. an RTL-SDR). I don't know of any open-source software which does that though I've been slowly building some for my own use (it's pretty janky at the moment).

This would be a great learning tool for those of us who are trying to learn it also.

[1] https://en.wikipedia.org/wiki/Definable_real_number