another variation of the sport, radio orienteering in a compact area, requires less athletic skill and more technical radio direction finding skills. in a roca course, the transmitters put out very little power, typically 10 to 200 mw, and can be received over only very short distances. the transmitters are physically small, and marked with a control card that is no larger than a typical postcard with a unique number identification. because of the low power and short distances involved, most roca competitors walk the entire course, and focus their attention on the radio direction finding tasks rather than navigation.