[plt-scheme] defmacro (define-macro) and hygienic macros

I have a question about macros in general:

When I look at the documentation for defmacro, I see that a
datum->syntax-object and back again is used, but I was under the
impression that unhygienic macros were just that because they were
lower level or less sophisticated than hygienic macros, which are a
design improvement on macros, making them easier to use and
understand.  Am I on the wrong track here?

I am having problems finding where the definition for define-syntax
is, so cannot see how it is constructed, but maybe it is done in c.
If anyone could point me in the right direction here it would be much
appreciated. 

Thanks,

rohan