A mechanism for identifying a low performing radio branch at a radio transceiver device. A method is performed by the radio transceiver device that comprises transmitting a reference signal for at least some of the N radio branches in a respective test period. The reference signal in each test period is transmitted according to a test configuration that specifies that during each test period the reference signal is mapped to only one of the N radio branches such that in test period k, where k=1, . . . , N, the reference signal is only transmitted from radio branch k. The method comprises receiving at least one report from another radio transceiver device relating to measurements made by this so-called another radio transceiver device on the reference signal transmitted for these at least some of the N radio branches to identify which of the N radio branches is the low performing one.