Monopole antennas operating at lower frequencies, below 20 MHz, use the Earth as part of the antenna, as a conductive plane to reflect the radio waves. These include the T and inverted L antenna, umbrella antenna and the mast radiator used by AM radio stations. The feedline from the transmitter is connected between the antenna and ground, so it requires a grounding (Earthing) system under the antenna to make contact with the soil to collect the return current. In lower power transmitters and radio receivers, the ground connection can be as simple as one or more metal rods or stakes driven into the earth, or an electrical connection to a building's metal water piping which extends into the earth. However, in transmitting antennas the ground system carries the full output current of the transmitter, so the resistance of the ground contact can be a major loss of transmitter power. The ground system functions as a capacitor plate, to receive the displacement current from the antenna and return it to the ground side of the transmitter's feedline, so it must be located directly under the antenna.