Somehow [hvde] wound up with a CB radio that does AM and SSB on ... this frequency because it is easier to create an SSB signal at a fixed frequency. The Arduino drives a frequency synthesizer ...

(A typical CB radio uses two "sideband" signals to carry a voice; SSB only uses one.) GMRS also uses Frequency Modulation (FM) as compared to CB radio, which uses Amplitude Modulation (AM).