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Passive coherent location (PCL) systems are a variant of bistatic radar that exploit 'illuminators of opportunity' as their sources of radar transmission. Dispensing with the need for a dedicated transmitter makes PCL inherently low cost, and hence attractive for a broad range of applications. Although a number of experimental and development examples exist, relatively little has been reported on the detailed performance of these systems and the resulting effects that these will have on the interpretation of backscatter and exploitation of derived information. In this paper, a bistatic form of the radar range equation, specifically tailored to PCL systems, is developed. Realistic examples are used to examine and compare variations in sensitivity and coverage for three candidate transmitters of opportunity. These are analogue FM radio, cellular phone base stations and digital audio broadcast (DAB). These examples show that a wide and extremely useful set of detection ranges are achievable and also highlight some of the key issues underpinning more detailed aspects of predicting detection performance.