Avionics Project

Hey again, I pretty much told use what i was doing for my project in my other thread. Erm, I think it was Ash that mentioned doing some sort of practical, basically I dont have time to do any sort of practical because my folder has to be re-submitted on monday again. The only requirement I need at the minute is suggestion of a circuit that I could look at and describe how the circuit works. The circuit would have to be something ivolved with navigation systems or communication systems, help would be much appreciated. 😛