Hi Stepper,
What we mean by this is the following:
On the FMCOMMS2 board we are using a 2.4GHz Balun with a narrow band maybe 1.6 to 3.3 GHz.
This Balun has excellent performance at 2.4GHz which is the frequency it was intended to work at.
However across the 70MHz to 6GHz it will not work because it is not design for such wide range.
On the FMCOMMS3 board, we use the TCM1-63AX+ transformer which is design to operate from 10MHz to 6GHz and so, it will maintain better performance through the whole range when compare to the Balun that is on the FMCOMMS2 board.
So our terminology refers to the FMCOMMS2 board as the RF engineer platform (because RF engineers will replace the Balun if they are interested in a different frequency) where as the FMCOMMS3 is more designed for software defined radio where no components replacement is needed and you still get good performance over the whole tuning range.
I hope that explains it.
Charly