I get two different dBm readings but the same V/m reading when using the MCS software using the following calibration settings:

1- Setting= BicoLOG Antenna 5070X, External Pre-Amp=None
Signal Level = ~ -32.21 dBm
V/m = 668.77 u V/m

2- Setting= BicoLOG Antenna 5070, External Pre-Amp= UBBV2
Signal Level = ~ -72.48 dBm
V/m = 674.18 u V/m

It might be confusing but both setups are correct and show the real FIELD STRENGTH and POWER DENSITY values.
The problem is that you are also looking on the dBm readings which is NONSENS if you use an antenna.

So why are both setups giving different dBm readings but the same V/m or W/m² readings? The answer is quite simple:
- The BicoLOG 5070"X" (active antenna) file is an 100% ANTENNA file, so it will give you NO changes in the dBm readings if you select it in the calibration setup. This is physical logical and 100% correct. It will ONLY influence FIELD STRENGTH or POWER DENSITY measurements.
- Instead if you use the BicoLOG 5070 (passive antenna) PLUS the UBBV2 preamp file (indeed physical the same as the Bicolog 5070X) you have two DIFFERENT files: An antenna file (which again will give NO changes in the dBm readings) PLUS a preamp file (which WILL change the dBm readings: The preamp file reduces the dBm reading by the dB amplification of the preamp). So all in all THIS setup indeed will give you a change in the dBm reading but this makes no sense to the measurement.

So all in all it simply does not matter if you use the "X" antenna file or just add the UBBV2 file to the “non active” antenna file AS LONG AS YOU MEASURE FIELD STRENGTH OR POWER DENSITY. BOTH will give you the same results.