Passive radar systems that exploit signals from the plethora of RF emissions that exist in the external environment offer a number of advantages over conventional active radar system, including procurement and operational cost saving. Each emitter has its own characteristics, including waveforms, which dictate system performance. BAE Systems Advanced Technology Centre has designed and built a demonstrator system to act as a test bed for passive sensor research. The system operates over a multi-octave bandwidth and can exploit both analogue and digital transmissions from both broadcast and communication systems. This offers advantages over single band systems; for example, multiple observations in different bands using different geometries allow fusion of tracks to achieve more robust and accurate tracks. This paper outlines the system and design issues that were addressed during the development of the demonstrator, including the simulation model, and prediction of bistatic target signature. Results of experimental work illustrating the operation of the demonstrator system with targets of opportunity are shown.