Hello everyone!
I came across a strange behavior of the SX1276 transceiver (and probably others in the SX127x series). When attempting to send data with inverted IQ from one SX1276 to another, I found that I was unable to receive the data if both devices were configured the same way (i.e., both configured to inverted IQ or both to non-inverted). I was able to receive only when the devices were configured opposite to one another.
To me this was rather strange, so I took a couple SDR recordings:
The first one is when I manually invert the IQ on the transmitter, the second one is when manually setting non-inverted IQ and the third one is when using the default configuration (without touching RegInvertIQ). What strikes me as odd is that the transmission from default configuration seems to match the “inverted” configuration - I would expect the opposite. Here’s the relevant register from rev 7 of the datasheet:
Is it possible that the logic of the InvertIQ TX bit in the RegInvertIQ is swapped? Neither the datasheet nor the errata say nothing about this, but I think this issue was encountered before in this post: https://forum.lora-developers.semtech.com/t/troubles-setting-up-the-sx1272-to-receive-a-packet-please-help/1245
Thanks!