Two forms of transmitting antennas are employed. Most commonly used are standard non-directional vertical antennas. However, an alternate implementation, called "leaky cable", is a form of carrier current transmission, which employs long horizontal conductors, commonly run alongside roadways. Stations using a standard antenna are generally limited to a coverage radius of , with an antenna height of no more than 15 meters (49.2 feet), and a maximum power of 10 watts, although critical evacuation systems, such as those in the Florida Keys and near chemical and nuclear facilities, have been granted waivers to exceed that limit for emergency operations, typically for up to 100 watts.