A first transceiver and a method performed by the first transceiver for monitoring a fiber cable. The first transceiver is connectable to a second transceiver by the fiber cable. The transceivers employ SCM analog modulation where baseband is dedicated for monitoring and the subcarriers are dedicated for data transmission. The method comprises receiving, from a device, at least one electromagnetic data signal to be transmitted towards the second transceiver on the fiber cable, and shifting the at least one data signal in the frequency domain. The method further comprises generating an electromagnetic test signal in a base band, combining the at least one data signal and the generated test signal, and modulating the combined data signal and test signal to respective optical carrier. The method further comprises transmitting the modulated data signal and generated test signal on the fiber cable towards the second transceiver.