What is the stage in a VHF FM transmitter that generates a harmonic of a lower frequency signal to reach the desired operating frequency?

A 'multiplier' (or frequency multiplier) is a circuit stage designed to take an input signal and output a harmonic multiple of that exact frequency, such as doubling or tripling it. In older or simpler VHF FM transmitters, it is easier and more stable to generate an FM signal at a lower frequency (like the HF range). That lower frequency signal is then passed through a multiplier stage to mathematically step it up to the final VHF operating frequency. A mixer combines two different signals rather than multiplying a single signal's frequency, and a reactance modulator is the component used to actually create the FM modulation itself, not step up its frequency.