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I'm using SX1262 radios in a custom network. I noticed that with SF5 spreading I miss about 12% of frames. This does not happen with SF6 and above, the BW (I use 500kHz) does not make any difference.

I tried several available libraries, using provided examples and only changing the SF, but the problem persists with them all.

Has anyone run into this, and if so, is there a solution?

Added from answer, which should have been a comment or edit here

I'm using the correct sync word. If I didn't nothing would be received, and I am only missing 12% of frames. Also, I am not using LoRa gateways. This is a custom network.

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  • What is your setup? How far apart are the devices? Do you have line of sight? What type of antennas do you use? What RSSI and SNR do you measure? The lower the SF the worse the sensitivity, so it may explain things if you are right at the limit. Also, did you correctly use the 12-symbol preamble, and are both transmitter and receiver only SX1262? SF5 and SF6 are not quite standard and details have changed between Semtech chip generations. Commented Dec 27, 2024 at 12:39
  • Both devices are on the bench in the lab. TX is set to 0dbm, and signals and SNR are maxed out. The measured RX frequency is only 60Hz off. CR=5. Yes, I made sure the preamble is set accordingly... I even tried more than 12. Everything is optimal, and it looks like an undocumented issue with SX1262 at SF5. I need to keep time on air to a minimum in the network due to battery issues, and am not interested in range over LOS, as nodes form a mesh. Commented Dec 27, 2024 at 14:31
  • P.S. Both devices (RX/TX) have 20db attenuators on the antennas, to ensure no receiver blocking from strong signals. There is no interference on the frequency. Measured RSSI is -30dbm with excellent SNR. However, the frames simply miss now and then. Not related to frame rate. Commented Dec 27, 2024 at 14:37
  • If you have another device it n would be interesting to see if two receivers miss the same frames from the transmitter or if the errors are independent. Also, is there any kind of pattern in the missed frames? And wouldn’t GFSK be a better alternative? Commented Dec 30, 2024 at 10:43
  • I do, and they both behave exactly the same, but miss different frames. It is easy to tell as the LED flashes on every message, and rate is 4 per sec. When frames are missed, it is sometimes 2 or 3. Again, just changing to SF6, problems go away. Sadly, I have to use SF5. Commented Dec 30, 2024 at 14:46

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Are you using sync word 0x12?

SF5 cannot encode sync word 0x34.

The LoRa gateways fix SF5 and SF6 to using 0x12. https://github.com/Lora-net/sx1302_hal/issues/124

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