The following are a set of links to websites and resources that I think are valuable or interesting. The topics and links are listed in alphabetical order.
Communication Systems
Introduction to the Controller Area Network (CAN) - Steve Corrigan
Radio
High Frequency VCO Design and Schematics
PLL Performance, Simulation, and Design - Dean Banerjee
Software Architecture
Architectural Styles and the Design of Network-based Software Architectures - Roy Fielding