The rinex files downloaded from the government antennas are RINEX 2.11 and in the post-processing tutorial of Emlid they ask that the ubx of the rover be converted to version 3.03 with rtkconv. So, I can work in rtkpost with the rinex 2.11 of the rover and the rinex 3.03 of the base antenna or I have to match them in the same rinex version.