This paper details the architecture for a minimal commensal radar system which makes use of commercial FM broadcast band transmitters for the detection of aircraft. The architecture, consisting of a RF front-end, digital acquisition and radar signal processing up to the detection stage (after CFAR on a Range-Doppler plot), is intended to be small, easily portable, low power, and yet able to operate in real-time. The system is based mostly on low cost commercial off-the-shelf (COTS) components. To this end, an Ettus Research USRP board, a NVIDIA Jetson TK1 computing board and connectorised RF components are exploited. It is shown that the presented system is able to detect commercial airliners in excess of 100 km from the receiver while providing output in a real-time streaming manner.