A system for directionally classifying of a radio signal originating from an emitter. The system includes a receiving-station, which includes at least two antennas, a single-channel-receiver producing a first and a second received signals and a switch alternately coupling each of the antennas with the single-channel-receiver. The system further includes another receiving-station which includes another receiver, producing another received signal, coupled with a first other antenna. The system further includes directional-classifier which includes a phase-difference-detector, coupled with the single-channel-receiver and with said another receiver. The phase-difference-detector produces a first phase difference measurement when the switch couples one antenna with the single-channel-receiver. The phase-difference-detector further produces a second phase-difference-measurement when the switch couples the other antenna with the single-channel-receiver. The directional classifier subtracts the second phase-difference-measurement from the first-phase-difference measurement producing a phase-difference-estimate. The receiving station and the other receiving station are in relative motion one with respect to the other.