LoRa

LoRa is a RF modulation technology engineered to be quite resilient to allow long-distance communications with a relatively low power-consumption.

It is also referred to as LoRa PHY.

Max Message Length

⚠️ Do not confuse with LoRaWAN limits ⚠️

Due to some legal limitations regarding the maximum RF air-time that can be used by LoRa, there is a limit to how long each packet can be.

If given more data than what should be transmitted in a single packet, the E32 modules will segment that data and transfer it as individual packets.

This automatic segmentation can be a problem in fixed transmissions since it completely erase the target address and channel from any subsequent packet.

This limit can be somewhat ignored when using transparent communications since the message doesn’t contain the target address and channel, but steps should be taken to not rely on this behaviour.

Official limits

I couldn’t find any concrete limits for packet size on LoRa PHY.

All I know is that is depends on a maximum air-time limit enforced by local RF laws which is defined by the air data rate and some other parameters.

As of now, you should try different sizes at your desired operating settings in fixed mode to find that limit.

Here is an excerpt from the “LoraWAN Regional Parameters RP002-1.0.4” document:

Mention of PHY restrictions influencing LoRaWAN max packet size.

Mention of PHY restrictions finfluencing LoRaWAN max packet size.

Observed limits

TODO: Check if it depends on the spread factor or just operating parameters and region.

If you can, please contribute to these tables by raising an issue.

Documentation

LoRaWAN Packet Size Considerations (By The Things Network)

Spreading Factor (SF)

The spreading factor is a mechanism that influence the air data rate, time-on-air and the receiver’s sensitivity.
It can be one of 6 values between SF7 and SF12.

I can’t for the life of me give you a clear and concise explanation or table of these values and their effect as well as the operating parameters that would be appropriate for them.
Absolutely nobody who should be able to can make a document that is concise, complete and doesn’t expect the reader to glue bits and pieces from 20+ different documents to get a complete view that doesn’t only cover part of these SF values because of some arcane reasons.

Here are some links to documentation I’d recommend on the subject:

Good luck.