the radio equipment carried on course must be capable of receiving the signal being transmitted by the five transmitters and useful for radio direction finding. this includes a radio receiver that can tune in the specific frequency of transmission being used for the event, an attenuator or variable gain control, and a directional antenna. directional antennas are more sensitive to radio signals arriving from some directions than others. most equipment designs integrate all three components into one handheld device. on the two meter band, the most common directional antennas used by competitors are two or three element yagi antennas made from flexible steel tape. this kind of antenna has a cardioid receiving pattern, which means that it has one peak direction where the received signal will be the strongest, and a null direction, 180° from the peak, in which the received signal will be the weakest. flexible steel tape enables the antenna elements to flex and not break when encountering vegetation in the forest. on the eighty meter band, two common receiver design approaches are to use either a small loop antenna or an even smaller loop antenna wound around a ferrite rod. these antennas have a bidirectional receiving pattern, with two peak directions 180° apart from one another and two null directions 180° apart from one another. the peak directions are 90° offset from the null directions. a small vertical antenna element can be combined with the loop or ferrite rod antenna to change the receiving pattern to a cardioid shape, but the resulting null in the cardioid is not as sensitive as the nulls in the bidirectional receiving pattern. a switch is often used to allow the competitor to select the bidirectional or cardioid patterns at any moment. ardf receiver equipment is designed to be lightweight and easy to operate while the competitor is in motion as well as rugged enough to withstand use in areas of thick vegetation.