Harmonics produced in an early stage of a transmitter may be reduced in a later stage by:

A tuned circuit consists of an inductor and a capacitor resonating at a specific frequency. When used to couple one transmitter stage to the next, it functions as a highly effective band-pass filter. Because the tuned circuit is designed to allow signals at or very near its resonant frequency to pass easily, it heavily attenuates signals at other frequencies. This ensures the desired fundamental frequency transfers efficiently to the next stage, while harmonics (which are multiples of the fundamental frequency) are effectively blocked. Using larger coupling capacitors, as suggested in one distractor, would actually allow higher-frequency harmonics to pass even more easily. Driving the final stage with greater input might push the amplifier into non-linear operation, thereby generating more harmonics rather than reducing them.