> Simple home-made driver for the SX1276 and SX1262 LoRa chip
Beware of what nailed the Meshtastic people: These chips don't have temperature dependent crystal oscillators. Transmitting more than a few milliseconds causing a temperature rise, throwing the clock off, causing transmission warpage, causing timing errors, causing transmission failures.
Temperature Compensated Crystal Oscillators (TCXOs) is what they should be looking for. And to be clear you can get SX1262 variants with such, eg: https://wiki.seeedstudio.com/wio_sx1262/
> In the case of an SX1262 operating at +22 dBm in the US 902 – 928 MHz band, the frequency drift measured during the maximum LoRAWAN™ packet duration stays below the maximum limit, provided thermal insulation is implemented around the crystal during PCB design.
> At extreme temperatures (below -20 °C and above 70 °C), it is recommended to use a TCXO.
> For any other frequency bands corresponding to longer RF packet transmissions at +22 dBm, it is recommended to use a TCXO.
Chat/text over LoRa always sounded intriguing! I'm merely a 1000km away from Sicily (which antirez say they wanna cover with the network at first), I wonder if it would be possible to do what AM radio does, bounce against the ionosphere and get huge ranges for transmission? Maybe it would need way too much transmission power? Maybe hopping all the way P2P style makes more sense, although surely would be slower.
Shame, but at least now I understand why, thanks :)
> you’re realistically limited to near line of sight paths
Wonder exactly how far one would be able to get up to reach 1,000km line of sight, assuming you put both points equally far up. Guessing it's the curvature of the earth that gets in the way at that distance?
Unlikely since the most ISM bands are UHF (EU is 868 MHz) and skywave propagation (what you’re referring to) is characteristic of HF radiation (3-30MHz). VHF/UHF radiation passes through the ionosphere instead of refracting.
I tried doing something like this on an ESP32 last year, I wanted to understand how to do an actual mesh with devices that can't transmit and receive at the same time, but I didn't find documentation.
I managed to get 2 devices communicating across town at least ! (After having antenna issues)
> Simple home-made driver for the SX1276 and SX1262 LoRa chip
Beware of what nailed the Meshtastic people: These chips don't have temperature dependent crystal oscillators. Transmitting more than a few milliseconds causing a temperature rise, throwing the clock off, causing transmission warpage, causing timing errors, causing transmission failures.
Temperature Compensated Crystal Oscillators (TCXOs) is what they should be looking for. And to be clear you can get SX1262 variants with such, eg: https://wiki.seeedstudio.com/wio_sx1262/
For the detailed run down, see https://cdn.sparkfun.com/assets/f/f/b/4/2/SX1262_AN-Recommen... page 14
> In the case of an SX1262 operating at +22 dBm in the US 902 – 928 MHz band, the frequency drift measured during the maximum LoRAWAN™ packet duration stays below the maximum limit, provided thermal insulation is implemented around the crystal during PCB design.
> At extreme temperatures (below -20 °C and above 70 °C), it is recommended to use a TCXO.
> For any other frequency bands corresponding to longer RF packet transmissions at +22 dBm, it is recommended to use a TCXO.
Theory and reality are different here.
As used in the meshtastic devices this chip does actually fail doing normal Lora transmission under reasonable conditions.
I know because I've seen the exact failure.
You mean they don't have temperature compensated? What you described is temperature dependent
too late to edit now :)
The chip itself supports using a TCXO instead of a regular crystal
This is a radio module issue, not a chip issue.
Cheap modules have cheap crystals, better ones have a TCXO.
Chat/text over LoRa always sounded intriguing! I'm merely a 1000km away from Sicily (which antirez say they wanna cover with the network at first), I wonder if it would be possible to do what AM radio does, bounce against the ionosphere and get huge ranges for transmission? Maybe it would need way too much transmission power? Maybe hopping all the way P2P style makes more sense, although surely would be slower.
Not at 900MHz. Skywave propagation mode is only available under about 30MHz. Above that, the signal reliably continues on into space.
At frequencies this high, you’re realistically limited to near line of sight paths.
> Not at 900MHz
Shame, but at least now I understand why, thanks :)
> you’re realistically limited to near line of sight paths
Wonder exactly how far one would be able to get up to reach 1,000km line of sight, assuming you put both points equally far up. Guessing it's the curvature of the earth that gets in the way at that distance?
Yep. There are cubesats running LoRa payloads in low earth orbit[0], and between mountaintops, terrestrial paths of hundreds of km are possible[1].
[0] https://www.hackster.io/news/fossasat-1-an-open-source-satel... [1] https://meshtastic.org/docs/overview/range-tests/
Checkout MeshCore; we're doing 400 miles using 12 hops going from north Vancouver to Eugene Oregon https://analyzer.letsme.sh/map?lat=47.36113&long=-122.20419&...
> 400 miles using 12 hops
What's the E2E latency on that, for curiosities sake :)
Unlikely since the most ISM bands are UHF (EU is 868 MHz) and skywave propagation (what you’re referring to) is characteristic of HF radiation (3-30MHz). VHF/UHF radiation passes through the ionosphere instead of refracting.
I tried doing something like this on an ESP32 last year, I wanted to understand how to do an actual mesh with devices that can't transmit and receive at the same time, but I didn't find documentation.
I managed to get 2 devices communicating across town at least ! (After having antenna issues)
Previously [2023]: https://news.ycombinator.com/item?id=35882967