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LoRa
Someone put together a nice google sheet calculator for airtime / time-on-air / transmission time.
The LoRa modulation scheme is closed and patented. I'm really hoping to have DisasterRadio v2 hardware using low bandwidth SDR instead of these chips. I know @papazoga is keen on working that. However, since no affordable transmit-capable SDR systems exist, for now these chips are our best bet at getting to prototype and v1.
The good news is that LoRa has been reverse-engineered and implemented as a GNU Radio module:
- Talk from GRCon16
- Slides from GRCon talk
- Talk from 33c3
- Technical writeup in PoC||GTFO
- GNU Radio module mentioned in GRCon talk
- Different LoRa GNU Radio module (based one the other one but this one is actually maintained)
The other good news is that transmit-capable SDR is expensive mostly because all of the existing SDR systems are extremely precise high-bandwidth systems capable of transmitting on 2+ GHz. We should be able to make a cheap send/receive SDR for low-bandwidth sub-Ghz operation (though it might be somewhat challenging to keep the power consumption low enough) but it's going to be a bunch more work than using an existing off-the-shelf LoRa chip.