Note on the Spreading Factors SF7 and SF12

  • SF7 is default and works perfectly. Messages need approx. 250 ms. Low range
  • SF12 is the largest spreading factor which does not always work reliably. Messages need approx. 6 s. Very high range

The spreading factors SF7 until SF11 work reliably with our LongRa and ECO Power boards. I prefer SF7 because this spreading factor has very short transmission delays and I do not need an extreme range.

SF12 entails the following problem: the frequency must be as exact as possible between all participants, but this is not the case. In my case, for example, two modules differ by approx. 4000 Hz, which is also displayed under “RxFrequencyOffset” when receiving. The following changes can be made in the configuration:

old: { 868100000, 125000, 14, 12, 0 }
new: { 868100000, 125000, 14, 12, 3890 }

Thus SF12 works with me too, but our LoRa modules have no TCXO, so the frequency between two modules varies depending on the different temperature.

At smaller bandwidths (e.g. 62,500 Hz instead of 125,000 Hz) the problem is even more serious; a TCXO is really needed here. A TCXO solution is currently not planned for cost reasons.