A balanced series mixer with a balun transformer (10)that has a high-frequency source port and an antenna port on one side, two diode ports on the other side, two diodes (20,22) that are switched between the diode ports and the high-frequency ground (24,26), and a wanted signal detection device (48) for a diode-generated mixed product of a high-frequency signal fed through the antenna port and a part of the high-frequency signal fed through the high-frequency source port, characterized by the fact that each of the diodes (20,22) are biased over bias-voltage leads (50,52) attached to the side of the high-frequency ground (24,26), that the diodes are separated with respect to direct current from the wanted signal device (48) and from the conductors (34,42) attached to the high-frequency source port and the antenna port, and that both bias-voltage leads (50, 52) have low-pass filters (54) constructed symmetrically to one another.