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SX1262 Message duplication

Hi,
I am using a RAK4631-based device that uses a SX1262 transceiver.
I am using just (private) LORA and interfacing directly with the lora-pkt-forwarder at the gateway.
Occasionally I get one or two duplicated messages sent from the device on a different frequency that of the first message. It only seems to happen with a spreading factor of 11.

I have debug output from my gateway software, below.
The first block of data is the rxpk message with 2 packets
Following that is my expansion of the data content showing that the packets come from the same device (field 2) and have the same f_cnt (field 5).

It is interesting that the two packets have very close tmst values.


{“rxpk”:[{“jver”:1,“tmst”:3942155167,“time”:“2022-01-18T09:55:50.201519Z”,“tmms”:1326534969201,“chan”:4,“rfch”:0,“freq”:867.300000,“mid”: 0,“stat”:1,“modu”:“LORA”,“datr”:“SF11BW125”,“codr”:“4/5”,“rssis”:-35,“lsnr”:10.5,“foff”:-50,“rssi”:-35,“size”:28,“data”:“AQGvdPxiLIrSBHwdGblQAPba+/+XAFoDANkAAA==”},{“jver”:1,“tmst”:3942155176,“time”:“2022-01-18T09:55:50.201528Z”,“tmms”:1326534969201,“chan”:1,“rfch”:1,“freq”:868.300000,“mid”: 3,“stat”:1,“modu”:“LORA”,“datr”:“SF11BW125”,“codr”:“4/5”,“rssis”:-114,“lsnr”:-19.5,“foff”:-111,“rssi”:-96,“size”:28,“data”:“AQGvdPxiLIrSBHwdGblQAPba+/+XAFoDANkAAA==”}]}

Received data: 1, af74fc, 622c8a, 1234, 7548, 5290265, -271626, 151, 90, 3, 217 Radio settings: SF11BW125, 4/5, 867.3

Received data: 1, af74fc, 622c8a, 1234, 7548, 5290265, -271626, 151, 90, 3, 217 Radio settings: SF11BW125, 4/5, 868.3


Thanks
Alan

I was hoping someone with more knowledge than me could shed some light on this behaviour and suggest how I could fix it,
Thanks
Alan