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SX1261 GetRssiInst setup time

Hi,
I’m doing some RSSI measurements with the SX1261.
In my test setup, after setting the transceiver to receive mode, I start reading the RSSI using the GetRssiInst function every 200us. I see that the value becomes constant and close to the right value after 20-25 measurements (this mean more than 4ms!).

The pseudo-code command sequence is:

  SX126xSetRx ();
  while (SX126xGetOperatingMode ()! = STATUS_RX) {}; // wait start reception
  for (uint8_t i = 0; i <100; i ++) {
      RSSIval [i] = SX126xGetRssiInst ();
      udelay (200);
  }

Is there an initial delay required before getting the correct and constant value?

Thank you,

What is your symbol duration? 4ms is a reasonable symbol duration. There are some app notes about getting stable RSSI samples on LoRa. If I recall correctly, it needs roughly 2 symbols, depending on SF and BW.

As you indicated, if I try to replicate the test with different SF and BW, the RSSI settling time changes. So that time window is related to the modulation parametes.
In my case the symbol time is less than a 1ms, so it’s mean that more than 2 symbols are required.

If you confirm that a few milliseconds are a reasonable time window for RSSI settling, then I can exclude that there are configuration errors on my part.

Thanks,

Caveat Emptor: I am a lora user, not a Semtech employee.

Anyway, I can confirm that lora rssi needs some time to settle. You can look at the app note for SX127x, which probably is similar for SX126x: AN1200.21 Reading channel RSSI during a CAD