If your Realflight G2 is the current, Interlink, version, it will not work without the Interlink controller (as the controller also serves as the copy protection device). If, from the other hand, your RF G2 is one of the pre-Interlink versions (i.e., it was originally sold with either a game port controller or a parallel port interface), any of the available TX-o-PC interfaces will work. I have an interface from www.milehighwings.com and it works fine with non-Interlink G2 as well as with many other sims.

Boris