ardf transmitters have a low power output and operate in either the two meter or eighty meter amateur radio band. the transmissions are in morse code. each transmitter sends a unique identification that can be easily interpreted even by those unfamiliar with the morse code by counting the number of dits that follow a series of dashes. the transmitters on course all transmit on the same frequency and each transmit in sequence for one minute at a time in a repeating cycle. within a few meters of each transmitter, an orienteering control flag and punch device will be present. for many events and all major events, the punch device is an electronic system, such as sportident, used in orienteering competitions. this records the time competitors visit each control on a small device that they carry. an alternative is to use pin punches which the competitor uses to make a distinct pattern on a control card they carry. competitors need to locate the control flag at the transmitter site and use the punch device to record their visit. good course design will attempt to preclude, as much as possible, runners interfering with the transmitter equipment as they approach the control. at large international or national events, jurors might be present at transmitter controls to ensure fair play.