Raymarine Wireless Mast Rotation Transmitter antennas am fm antennas when mounted with a WeatherDeck™ Extras::Boat,Console & Tank, Bolster Tube, Bench Seat, T Top, Hydraulic Steering & Trailer when mounted with a WeatherDeck™ Toggle Switch Boot (8 24138) complete the set up Operating as a wireless device on a Micronet network the Mast Rotation Transmitter compares compass information from the boat with its own information and corrects the wind angle coming from a standard wind transmitter at the mast head Easily installed at any convenient position on the mast the Mast Rotation Transmitter can be calibrated simply from any Digital or Dual Digital Display in the system