Hello there,
I’m working on a project requiring to transmit over Lora the RTK corrections obtained with a Sparkfun RTK Express in base mode. How would you connect the Express with any Lora transmitter? Anything else required?
LoRaPTP not LoRaWAN
Same Radio settings on each end.
Need transparent data movement, not adding any of your own data bytes, or losing them.
No point retrying, fresh data is baked continuously
Data may exceed LoRa packet sizes, I’d recommend aligning on RTCM3 packet boundaries, so they don’t span. Decompose large RTCM3 packets into two or three equal sized radio packets.
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Thanks for your fast answer; sorry I’m just a beginner. I was thinking to use SparkFun Pro RF or the RFD 900x-US Modem as radio. Do you have any suggestions on the easier brand/model to configure? Do you think that connecting the radio with the RTK express over LoraPtP with RTCM3?
As I recall the RFD 900x-US is a SiK radio (Si1000 from SiLabs) and not LoRa (Semtech)
Some serial modems have headers for destination station, packet/buffer limitations, etc, where as what you need is a transparent serial tunnel. But then you’re reliant on the modem watching for end-of-transmission.
Ideally you want some packet level awareness, the RTCM3 packets impart size, and have a CRC24 checksum for integrity. They can split over several radio packets/transmission, and you need to have them reassemble / concatenate at the far end. Having the RTCM3 packets unnecessarily span two radio packets simply based on being sent end-to-end and not an observable delay, make recovery and resync more difficult, or introduce unnecessary latency.
The RTK receivers don’t care how you move the data, just that data going in one end of the link appears at the other, nothing added, nothing lost. In the same order, and quickly.
The SiK modems used by 3DR/Mission Planner are fine. Similar LoRaPTP would also be fine. But got to read the data sheets, and configure appropriately.
I would avoid correction / retry options, it’s a waste of time/bandwidth. RTCM3 is a constant, evolving stream, the next packets will have newer / better data, the RTK receiver isn’t keeping a long historical log to match measurements, it wants current data, with low latency.
LoRaSerial should work
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