The SGC understood the functions of a dial-home device and was able to create their own when the gate they had didn't have a DHD.
I remember in one or two episodes there were issues that led to characters (like Samantha Carter) having to fix a Stargate. It looks like they had a clear understanding, at least after several years, of how the gate worked and what it took to repair it (in some situations).
Was there something, in particular, that was missing that kept the SGC from building their own Stargates? Perhaps a need for a rare material the gate needed? Or did they never reach the level of understanding of how a stargate worked to actually be able to build one?