47 CFR 95.859 - Antennas.
(a) The overall height from ground to topmost tip of the CTS antenna shall not exceed the height necessary to assure adequate service. Certain CTS antennas must be individually licensed to the 218-219 MHz System licensee (see § 95.811(b) of this part) and the antenna structures of which they are a part must be registered with the Commission (see part 17 of this chapter).
(c) The RTU may be connected to an external antenna not more than 6.1 m (20 feet) above ground or above an existing man-made structure (other than an antenna structure). Connectors that are used to connect RTUs to an external antenna shall not be of the types generally known as “F-type” or “BNC type.” Use of an external antenna is subject to § 95.861.