47 CFR § 95.787 - RCRS additional requirements.
Each RCRS transmitter type must be designed to satisfy all of the following additional requirements:
(2) The gain of the antenna must not exceed that of a half-wave dipole; and
(c) For RCRS transmitter types incorporating plug-in frequency-determining modules that are intended to be changed by the operator, the modules must be submitted for certification together with the transmitter type. Each module must contain all of the frequency determining circuitry including the oscillator. Plug-in crystals are not considered modules and must not be accessible to the user.