To convert the HCB-10C portable to a mobile radio: Disconnect the "Rubber Duck" or telescopic antenna and connect your vehicle/boat's mobile CB antenna (or optional magnetic mount antenna WTA-4W).NOTE: Mobile antennas utilize the vehicle's metal body as the "ground" plane. When mounted on the corner of the vehicle, this type of antenna tends to become slightly directional by the particular corner it is facing. (This slight directional characteristic will only occur when transmitting/ receiving over an extreme distance).