Explanation: The RF (Radio Frequency) stage is the first active component to process the extremely weak signal from the antenna. The noise figure of a receiver is primarily determined by this initial stage because any noise added here is amplified by all subsequent stages (mixer, IF amplifier, audio amplifier). While later stages like the IF strip and audio stage also introduce noise, their contributions are effectively *reduced* by the gain of the preceding stages. This means the noise from the RF stage, which amplifies both the signal and its own inherent noise, sets the fundamental noise floor for the entire receiver. The local oscillator generates a frequency but doesn't primarily establish the system's noise figure. Therefore, a low-noise RF amplifier is critical for good receiver sensitivity.