Hi @gonzalocasas,
Do you have a default configuration for the RN2483 to use TTN?. On the IMST im880a there is not much to setup, i'm using the LoRaWAN endnode studio from IMST to work with the radio. The only serious parameters that can be set are the following (the settings i'm using behind it):
device addres : 02030501
appskey : 2B7E151628AED2A6ABF7158809CF4F3C
netwkskey : 2B7E151628AED2A6ABF7158809CF4F3C
adaptive data rate : off
default rate : SF7, BW 125 khz (also tried 250 khz and SF12)
ABP
But unfortunately no packets received 
Kind regards,
Sven-Erik Haitjema