I'm very good at RF hardware and antenna design; grok that as I do it for a living.
I have dabbled in DSP and FPGAs, hacking some Verilog together with Xilinx blocks to do RF in to USB out. Not a DSP comms guru, but know my way around the theory.
Then got into GNU Radio, so had to learn Python. Got the basics down on that and wrote a GNU radio based app, putting it on Github.
Though then came C++, and the whole Linux development environment. Totally new stuff to delve into. Still trying to wrap my head around that.