Abstract: The stop-band and pass-band frequencies of a duplex filter which includes a plurality of helix resonators must not change when the temperature changes. Therefore the resonators used must be temperature compensated. One known method is to injection-mold plastic bonds (3, 8) to the cover (2) of the resonator shield in such a way that the last turns of the helical coil (4) of the resonator are inside the bond (3, 8). Through a suitable selection of the bonding material it is possible in part to compensate for changes in the distance between the open end of the resonator coil and the cover of the shield and for changes in the pitch of the turns of the conductor (4) wound into a helical coil and in the coil length. In practice this compensation is undercompensated in character. According to the invention it is possible, by making one interval (pitch) (7) between the free turns of the coil greater than the others, to make the temperature compensation just right.