A method for detecting a change of an impedance of a magnetic field receiver of a metal detector, including: having a first network of passive components, including the impedance of the magnetic field receiver having a second network of passive components, excluding the impedance of the magnetic field receiver and processing a first measurement signal from a first node of the first network with a second measurement signal from a second node of the second network to detect the change in the impedance of the magnetic field receiver wherein the first network, the second network, the first node, the second node is configured such that in an absence of an external influence which affects the impedance of the magnetic field receiver, the first measurement signal is substantially the same with the second measurement signal and in a presence of the external influence, the first measurement signal is different from the second measurement signal.
