Distinctive propulsion

Reading modulations In their Letter, the team from South Africa´s Council for Scientifi c and Industrial Research and the University of Cape Town present a method to extract the propeller speed of an approaching aircraft using CR signals, adding to the information available for recognising a target. Their approach uses the effect of a rotating propeller on the polarisation of refl ections of RF signals such as those emitted by FM-band commercial radio stations. The rotating propeller causes modulation in the polarisation of the refl ected waves, which can be observed as amplitude modulation of the signals received by the CR system.