controlling the common mode impedance for a circuit , conductor , or multiple conductor cable by incorporating the circuit or conductor into the primary of a transformer . the secondary of the transformer is coupled to a secondary impedance selected so that the desired impedance is obtained . a capacitive shunt may be added to buffer the intrinsic primary impedance . the intrinsic impedance of a conductive antenna structure is controlled by deploying a portion of the antenna structure as the primary of a transformer and coupling the secondary of the transformer to a selectable secondary impedance .