I need pypy to speed up my python code. While the pypy doesn't support a lot of modules I need (e.g. GNU Radio). Could I use pypy to speed up parts of my python code. Could I use pypy to only speed up some of my python files? How can I do that?
No, you can't. And GNU Radio does the signal processing and scheduling in C++, so that's totally opaque to your python interpreter. Also, GNU Radio itself is highly optimized and contains specialized implementations for most of the CPU intense tasks for SSE, SSE4, and some NEON. 

I need pypy to speed up my python code. 

I doubt that. If your program runs too slow, it's probably nothing your Python interpreter can solve -- you might have to look into what could take so much time, and solve this on a higher level.
Could pypy speed up parts of my python code?